Every term in the City & Guilds 8202-35 Advanced Technical Diploma, explained in plain English — 1720 words and abbreviations across all 6 units. The vocabulary comes from the standard rather than from general trade usage, because the words on the exam paper are the standard’s words. Where the trade has a second name for something, the definition says so.
Wearing away of a cable sheath by rubbing against a hard edge, typically at an unbushed metal knockout or where a cable crosses a sharp corner.
A bonded wheel used for cutting or grinding at high speed. It must be ring tested before use, fitted with manufacturer-recommended parts, and run with the guard close to the wheel.
0 K, or −273 °C, the temperature at which no heat energy remains. Everything warmer than this contains heat that a heat pump can in principle collect.
A material such as granules or pads kept in a spill kit, used to soak up a spilled liquid so that it can be collected and disposed of properly.
The coated surface inside a solar collector that receives solar radiation and passes the heat to the fluid circulating through it.
The element of a collector that receives and absorbs the solar radiation and converts it into heat, then passes it to the fluid in the tubes bonded to it.
A consent from the environmental regulator to take water from the ground or a watercourse. Open loop systems normally require one.
The fraction of an expansion vessel’s volume that is actually available to take expansion, the rest being taken up by the gas charge behind the diaphragm. It is 1 minus the charge pressure divided by the maximum pressure, both worked in absolute pressure.
The volume of expansion water a vessel will actually take. The practical figure is measured at 0.35 bar below the safety valve setting.
The planned means of getting to and from the place of work safely, such as the procedure for reaching a roof or entering an excavation, recorded in the method statement.
A small opening in a bolted cistern lid that lets the cistern be inspected, cleaned and its inlet valve adjusted without removing the whole cover.
A removable section of boxing or casing that lets a component behind it be reached for inspection, maintenance or replacement.
An opening in pipework, such as a cover, cap or clearing eye, provided so the pipe can be cleared and tested. It is positioned so its use will not cause a nuisance.
The record in which work-related injuries and incidents are entered, giving the details needed for investigation and for any report to the enforcing authority.
The examination of what actually happened after an accident or near miss, to find which control was missing, defeated or inadequate so that it can be put right.
A person who has passed an approved training course and is registered to commission and test RPZ valves. A new RPZ must be commissioned by one, and then tested every year, with the results sent to the water undertaker.
A vessel with water held against compressed air that keeps the system pressure up while the pumps are idle. On booster set diagrams it is also labelled the expansion vessel.
The HSE Approved Code of Practice on Legionella, which requires records of monitoring, inspection, tests and checks to be kept for at least five years.
The part of a risk assessment form listing further action required, who will carry it out, by when, and the date it was completed.
A cartridge that absorbs chlorine, pesticides, taste and colour. It can breed bacteria, so it is not used on water of unknown quality.
The area actually covered by the heating element, used when quoting output. For a plated floor it is the aluminium area alone, with joists and return bends deducted.
A solar thermal system in which a pump circulates the heat transfer fluid between collector and store.
The clear floor area in front of or beside an appliance that a person needs in order to use it, given in BS 6465-2. Activity spaces may overlap one another.
The small electrothermal head on the return manifold that closes a circuit when its room thermostat is satisfied.
Work that adds to or changes an existing installation, such as taking a new spur off a circuit. It triggers the checks of Regulation 132.16 and requires certification.
Extra protection against electric shock provided by a residual current device with the characteristics required by BS 7671, used where basic and fault protection alone are not enough.
Floors immediately next to one another. Stack test appliances are placed close to the top of the stack and on adjacent floors to give the worst pressure conditions.
A control that works through the organisation of the work, such as a safe system of work, a permit, training, sequencing, signs or supervision.
Air being drawn into or churned into system water, bringing oxygen that accelerates corrosion.
A tap outlet that mixes air into the stream so it feels fuller while using less water.
A one-way valve to BS EN 12380 fitted at the top of sanitary pipework. It admits air to relieve negative pressure but does not let foul air escape, allowing a stack to terminate inside a building.
How many times the air in a defined space is replaced each hour, found by dividing the volume of air passing through the room in an hour by the volume of the room.
On an accumulator charged from a main, the amount by which the air charge is set below the mains pressure so water can enter: about 1.5 bar, never less than 0.8 or more than 2 bar.
The compressor on a self-assembled set that keeps a pneumatic pressure vessel charged with filtered air.
A gap of open air between the lowest point of a water outlet and the spill-over level of the vessel or appliance it discharges into, so that no pipe joins the wholesome water to the contents. It is a non-mechanical backflow arrangement with nothing to wear or jam, and the only protection accepted for fluid category 5.
A valve at a high point that opens to let air into pipework as it drains. Without air entering, check valves at the outlets can hold a vacuum and a cylinder can collapse.
A pocket of air trapped at a high point in pipework or inside a pump that stops or reduces the flow of water. A pump is cleared by priming; pipework is avoided one by filling slowly with the highest outlet open.
A fitting that combines the vent, feed and system connections at the neutral point and removes entrained air from the circulating water.
A heat pump that extracts low-grade heat from outside air, drawn across an evaporator coil by a fan, and delivers it to a heating system.
A soundness test in which a section of pipework is sealed, pressurised with air and watched on a gauge for any drop in pressure. BS 8525-1 requires one on the wastewater connections and on the greywater distribution pipework before handover.
The ability of pipes, fittings and joints to hold a positive air pressure without leaking, so that foul air cannot escape into the building.
A vent or open tap at a high point through which air escapes as the system fills, closed once water shows at it.
A heat pump that takes heat from outside air and delivers it into the dwelling as warm air, usually through indoor fan units. It produces no domestic hot water.
Air trapped at a high point in pipework that stops or interrupts the flow of water. It is cleared by draining and refilling, or vented at the high point.
The proportion of incoming solar radiation reflected back to space by cloud, the atmosphere and the earth's surfaces.
Giving each operative responsibility for a defined part of the building, so that ownership of quality and the route for tracing a defect are both clear.
A WC cubicle sized and fitted with grab rails for a person who can walk but has limited mobility. Detailed in BS 8300.
The angle of a collector from the horizontal. In the UK the optimum is 30 to 40 degrees, with 35 degrees as a working default.
A trough from which livestock drink, fluid category 5 because of animal saliva and waste. It is filled through a type AA air gap: a rigidly fixed float valve in a locked, covered housing on the trough edge, with the water level at least 25 mm below spill-over.
In a galvanic cell, the less noble metal, which gives up electrons and is corroded away — zinc against copper, for example.
A valve on the expansion vessel connection that makes the vessel's contents exchange with the flow each time water is drawn, so the water in it cannot stagnate.
A trap fitted with a valve that admits air when negative pressure occurs, so the seal is not siphoned away. A resealing trap does a similar job by retaining part of its water.
A short flexible connection fitted at a pump's inlet and outlet to stop vibration passing into the pipework. If it is bent or distorted it restricts the flow.
A resilient mounting between a unit and its base or bracket that stops vibration passing into the structure.
The area of a solar collector that actually admits sunlight, used as the basis for sizing the solar coil and the dedicated storage volume.
The stage of the formal procedure at which an employee can challenge the decision made about them.
The plan area taken up by the appliance itself, including closely related pipework and fittings.
The contractor's monthly submission setting out the value of work done and materials on site, on which the interim payment is based.
A trainee learning the trade under supervision. They hold very little responsibility for installations and require full supervision at all times.
The first of the two Regulation 4 tests every water fitting must pass: it must be made to an appropriate British Standard or equivalent, or to a specification approved by the regulator. Conformity is usually shown by an approval mark or listing, but that is evidence, not the legal test itself.
Practical guidance approved by the HSE on how to comply with the law. Following it is enough to comply; departing from it means proving compliance another way if prosecuted.
A person approved by the water undertaker for the area, or certified by an organisation the regulator has specified in writing, to install water fittings. An approved contractor need not notify items 2, 4(b) and 4(g) (alterations on premises other than a house, ascending-spray bidets and RPZ valves) but must give a certificate of compliance to the customer, and that certificate gives the customer a statutory defence.
Official guidance published to show how the requirements of a part of the Building Regulations can be met. Following it is the normal route to compliance.
The government guidance on meeting Part G of the Building Regulations 2010 (sanitation, hot water safety and water efficiency). Its section on cold water says supply from an undertaker through an installation complying with the Water Fittings Regulations may be assumed wholesome, and it lists the competent person schemes that can self-certify.
The Building Regulations guidance on conservation of fuel and power. It sets efficiency, insulation, controls and commissioning provisions for dwellings, and is supported by a compliance guide.
The Building Regulations approved document covering electrical safety in dwellings, under which electrical work on heating controls is certificated.
A private body approved to carry out the building control function in place of the local authority, working under an initial notice.
A test instrument made to GS38 for proving a circuit dead. It is proved on a known supply or proving unit before and after the test.
A test instrument suitable for proving a circuit dead. Volt sticks and neon screwdrivers are not suitable for the purpose.
A layer of rock or gravel that holds ground water like a sponge, from which wells and boreholes draw.
The designer who turns the client's requirements into a building design and working drawings, oversees the work until handover and administers the contract.
A direction by which a local authority withdraws permitted development rights in a defined area, so an application is needed for work that would otherwise be allowed.
Drawings and records showing what was actually installed, as distinct from what was designed, provided at handover as the contract requires.
A drawing or schematic of an existing installation showing the pipework as it was actually installed, consulted so that only the intended parts of a system are worked on.
A fibrous mineral used in older buildings for insulation and boarding. Its dangerous form is airborne dust, which causes fatal lung disease when inhaled.
A bidet whose spray comes up from below the rim, or that has a flexible hose, so that the outlet can be submerged in used water. It is a fluid category 5 risk, must be fed from a dedicated cistern or through a suitable backflow arrangement, and is notifiable under item 4(b) of Regulation 5.
The dates and hours during which the team will be on site, recorded in the method statement so that the client and other trades can plan around them.
Holding surface water back in storage, such as a detention pond, so the peak rate of flow passed on to a sewer or watercourse is reduced.
A valve on the upstand of a drinking water header that lets air in and out as the water level in the header rises and falls.
A valve fitted at a high point that vents trapped air from the system automatically as it collects.
A float-operated vent fitted at a high point that releases air from the system automatically as it collects.
A spring-loaded differential pressure valve connecting flow to return, which opens on system pressure when the zone valves and TRVs close, maintaining a minimum flow through the boiler.
An irrigation system that runs without someone holding the hose, such as sprinklers, drip lines or porous hoses on a timer. It is a Regulation 5 notifiable fitting and, with buried or porous parts, fluid category 4 in a house garden and 5 elsewhere.
A control facility that lowers the room temperature setting at night or during unoccupied periods instead of switching a slow system off.
A cistern that fills slowly and siphons to flush the urinals whenever it is full, limited by Schedule 2 paragraph 25 to 10 or 7.5 litres per hour per bowl.
The second heat source, usually a boiler or an immersion heater, that a solar system must have available so the water can be brought up to temperature when there is not enough sun.
The switch inside a motorised valve head that makes when the valve reaches its open position, sending the switched live on to the boiler and pump.
The pressure that can be used to push water through the pipe to an outlet. For a cistern-fed system it is the vertical distance from the base of the cistern to the outlet; for a mains-fed system it is the minimum mains pressure at peak demand, less any rise to the outlet.
The 23.5 degree tilt of the Earth's axis relative to its orbital plane, which causes the seasons by changing day length and the angle of the beam.
The compass direction a collector faces, measured from due south. Due south is 0 degrees, south-west plus 45 degrees, due west plus 90 degrees.
Backflow caused by the pressure on the consumer's side rising above the supply pressure, so water is pushed back towards the main. A pump, expansion in a hot water system or a burst main with the consumer's pipework still full can all cause it.
Backflow caused by a negative pressure in the supply pipe sucking water back through a submerged outlet, like drinking through a straw. A burst main while a hose lies in a bath, pond or pool is the classic case.
The wholesome water supply that makes up the shortfall when a rainwater or greywater store runs low. It must be protected by an air gap and fitted with a warning mechanism.
A voltage reaching a terminal by another route through the circuit, which produces false readings unless the terminal is disconnected during testing.
Refilling a trench over underground pipework. The pipe is inspected and tested before it is backfilled.
Water flowing in the wrong direction, from a fitting or appliance back towards the supply, either because the supply pressure drops (back-siphonage) or because the downstream pressure is higher (back pressure). It is the main route by which contamination reaches the mains, so Schedule 2 paragraph 15 requires a backflow prevention device matched to the fluid category.
A fitting or arrangement that stops water flowing back towards the supply: an air gap, a check valve, a double check valve, an RPZ valve or a pipe interrupter, chosen to match the fluid category of the risk. Mechanical ones must be made of gunmetal or dezincification-resistant material and must be accessible for testing and renewal.
A rise in the discharge pipe from a lifting plant that goes above the level of the sewer before dropping into the drain, so the sewer cannot flow back into the unit.
A fitting that stops water flowing backwards from a system into the supply — an air gap, check valve, pipe interrupter or RPZ valve — chosen to suit the fluid category of the risk. They contain springs, seats and diaphragms that wear, so BS EN 806-5 Annex B sets out how each type is tested and maintained.
Heating that holds the whole property at a reduced temperature rather than at full comfort. It takes the chill off and protects against frost and condensation.
Cleaning a sand or pressure filter by reversing the flow through the bed to flush out the trapped sediment.
A water sample taken two to seven days after disinfection and analysed for micro-organisms to prove the treatment worked.
The cold water take-off to the outlets, made after the pressure reducing valve and before the single check valve, so hot and cold reach mixers at comparable pressures.
A cold water supply taken from the cold feed to an unvented cylinder, downstream of the pressure reducing valve, so that hot and cold arrive at a mixer at the same pressure.
A cold connection taken downstream of the pressure reducing valve on an unvented system, so hot and cold reach a mixer at the same pressure and the blend stays stable.
Hot and cold supplies arriving at a mixing valve at similar pressures, needed by some mixers and not by others.
Adjusting regulating or pressure reducing valves so that every outlet gets its design flow and pressure rather than the nearest taking everything.
The record of the balancing exercise: the valve settings applied and the flow rates or temperature differences achieved on each circuit. BS EN 14336 includes it in the handover documentation.
In this lesson, a quarter-turn valve with a drilled ball that turns to open or close the way — not a float valve. It is a good servicing valve because the lever shows at a glance whether it is open and it is not easily knocked.
The unit of pressure used for testing; 1.5 times a 3 bar working pressure is 4.5 bar.
Pressure measured from a complete vacuum rather than from atmospheric pressure. It equals the gauge reading plus 1 bar, and both pressures in the vessel formula are absolute.
Plastic heating pipe made with an oxygen barrier layer in the wall. It stops oxygen diffusing into the system water and corroding ferrous components.
A water softener that swaps the calcium and magnesium that make water hard for sodium. Checked with pH strips and a hardness test.
A measured value recorded at commissioning so that a later reading can be compared with it. Without a baseline, a later measurement cannot show whether anything has changed.
Protection against electric shock under fault-free conditions, provided by insulation of live parts and by barriers or enclosures.
A bath filler with a diverter and a flexible shower hose, fed by hot and cold supplies. Because the hose can drop into the bath water it needs category 3 protection: double check valves on both feeds, a retaining ring, or a built-in type HC diverter.
A bath tap with a diverter and flexible shower hose, designed for equal hot and cold pressures.
Greywater from baths, wash and hand basins, showers and clothes washing machines. It is the source covered by BS 8525-1.
A timber fixed into a wall or studwork to give a solid fixing point for an appliance, radiator or bracket.
The usual radiator connection arrangement, with flow and return entering the bottom of the radiator at opposite ends.
The timbers or supports on which a cold water storage cistern sits. They must be sound and able to carry the cistern filled to the rim, spreading the load across the whole base.
The industry commissioning checklist and logbook for heating and hot water appliances, recording installer details and the safety-critical checks made at commissioning.
The commissioning checklist and service log supplied in the boiler literature, completed at handover and left with the customer.
The industry checklist supplied in the back of most appliance manuals, completed by the person commissioning the system to show that the checks were made and the results were satisfactory.
A mixer tap or shower fitting whose hot and cold waterways stay separate all the way to the outlet, so the two waters only meet in the air. Because hot cannot cross into cold inside it, BS 8558 does not require check valves on its feeds.
A tap with a horizontal inlet, fixed to a wall or pipe rather than to the appliance; hose union taps and the taps over a cleaner's sink are bib taps. Over a sink it must be set high enough for the AUK3 gap.
A document prepared by the quantity surveyor from the architect's drawings that lists every item of labour and material for a job, so contractors can price it line by line. With the floor plan it is the pair used to cost a job before it starts.
The most advanced domestic greywater system, combining filtration, bio-culture treatment with settlement and a UV filter before storage.
An additive that inhibits microbiological growth. BS 7593 asks for it to be considered on systems designed to run below 60 °C.
Biological material burned to produce heat. The main domestic fuel is wood pellets, with logs and wood chips as alternatives.
The outdoor temperature at which the second heat generator in a bivalent system has to start contributing.
A system using two or more heat generators of different kinds, such as a heat pump with a boiler or an electric heater.
Wastewater containing faecal matter and urine, such as WC discharge. It goes to the foul drain and cannot be re-used within a building.
The synthetic rubber (neoprene) bag inside an accumulator that holds the water, with compressed air around it.
An expansion vessel in which the water is contained inside a neoprene bag, so it never touches the steel shell. This is the type used on unvented hot water systems.
The volume of usable warm water a store yields once it is mixed with cold at the outlet. Stored water at 60 degrees goes further than its own volume when blended down to 40.
A thermostatic mixing valve on an underfloor manifold that mixes hot primary flow with cooled return water to give the low temperature the floor circuits need.
A small-scale plan showing where the site sits among the neighbouring buildings and roads. It is drawn at a smaller scale than a site plan and is too small to locate a stop valve or a pipe.
A copper-pipe problem in which very fine copper corrosion products turn the first draw of water blue-green and stain sanitaryware. It is caused by water standing in copper pipe — especially new pipe that has not yet formed its protective film, or pipe with flux left inside — and is cured by thorough flushing.
A wiring arrangement interconnecting the system controls so that the boiler and pump are switched off when there is no demand for space heating or hot water. It is not a physical device.
An electronic controller that monitors temperatures and system operation and adjusts times and setpoints automatically, learning how the building heats and cools.
A set of pumps drawing from a break cistern to raise the pressure in a building's cold water system. Each pump outlet carries a single check valve so water cannot drain back through an idle pump to the cistern.
A system in which pumps raise the pressure, either from a break cistern (indirect boosting) or from the supply pipe with the undertaker's consent (direct boosting).
A pump fitted to raise the pressure of an incoming supply. Taken directly from the main it may not deliver more than 12 litres per minute.
The assembly of pumps, controls and vessel that raises cold water to the floors the main cannot serve.
The inside diameter of a pipe. A rough or scaled bore, a small bore and every extra tee or elbow all cost pressure between the main and the outlet.
A drilled hole 100 to 150 mm across, reaching up to about 50 m into an aquifer, from which water is lifted by a submersible pump.
A vertical ground collector installed in a drilled and grouted borehole, used where the land available for trenches is limited.
A moulded or strap fitting on a stack or branch that takes a small waste pipe, such as a 32 mm or 40 mm branch, into a larger pipe.
A trap with a dip tube or vane inside a cylindrical body, the lower part of which unscrews for access. BS EN 12056-2 ND.2.3 restricts it to wash basins.
The water undertaker's stop valve at the boundary of each property, where the communication pipe from the main ends and the consumer's supply pipe begins. Its position on a new estate is found on the site plan.
A dial pressure gauge worked by a curved tube that straightens under pressure, fitted on pump inlet and outlet to show the pump is delivering.
A towed water tank used on site. Its water is not fluid category 1 and must not be used to fill a drinking water system.
The gas law that the pressure of a fixed mass of gas rises as its volume falls, which decides how much water a vessel can deliver between cut-out and cut-in.
The pipe carrying the discharge from one or more appliances to a discharge stack, another branch or a drain.
A ventilating pipe connected to a branch discharge pipe within 750 mm of the trap, which limits pressure changes and protects the seal.
A low-level cistern filled from the main through a float valve, from which booster pumps draw. It breaks the connection between the pumps and the main.
Maintenance carried out in response to plant having already failed.
The signed record showing that each person working under a method statement or risk assessment has received and understood the briefing on it.
The water and antifreeze mixture circulated through a ground collector to carry heat to the heat pump. Its pressure and strength are checked at service.
The sealed circuit between the ground collector and the heat pump evaporator, containing the antifreeze mixture. Its pressure is recorded at commissioning as a leak baseline.
One of the third-party certification bodies whose approval of an unvented unit or package is accepted as evidence that it meets the Building Regulations.
A published set of recommendations for design, materials or workmanship, prefixed BS, or BS EN where it is a European standard adopted in the UK. It is not law, but following it is the accepted way of showing the Regulations have been met and the water undertaker will expect to see it.
The British Standard for identifying the contents of pipes by colour. Water pipes get a green base colour, with an auxiliary blue band for fresh (cold, drinking) water and safety red for fire-fighting water, so non-wholesome pipework can be told apart at a glance.
The British Standard schedule of paint colours, which gives each colour a code. The pipe identification green of BS 1710 is BS 4800 12 D 45.
The former British Standard for hot and cold water services in buildings, withdrawn when BS EN 806 was completed. Its method and some of its figures, such as the 230 litre cistern minimum and the 3 m/s velocity limit, still appear on older drawings and in older specifications.
The British Standard test for the effect of non-metallic materials (plastics, rubbers, coatings, jointing compounds) on water intended for human consumption. It checks taste, odour, appearance, toxic substances and whether the material supports the growth of micro-organisms; a material that passes is suitable for contact with drinking water.
The British Standard for the preparation, commissioning and maintenance of system water in a heating system, including cleaning, flushing and inhibitor.
The IET Wiring Regulations, the British Standard for electrical installations. It has nothing to do with sizing a cold water pipe, though the numbers look familiar enough to reach for on a mixed-services job.
The British Standard code of practice for workmanship on hot and cold water services; clause 3.7.6 repeats the location rules for mechanical backflow devices: accessible, inside, not buried, not in a floodable chamber.
The British Standard for rainwater harvesting systems: their design, installation, water quality, identification of pipework and the need to notify the water supplier before work starts on a site with a mains supply. It also sets out the dry-run protection needed on harvesting pumps.
The British Standard code of practice for greywater systems. It requires greywater pipework to be green or black and green and never blue, storage tanks to be marked, and a flush and air or dye test before handover to prove there is no cross connection.
The British guide that sits alongside BS EN 806 and gives the UK detail for designing, installing, commissioning and maintaining water services in buildings, including booster sets, cisterns and backflow protection. It replaced BS 6700, which is still quoted for figures BS 8558 no longer gives.
The standard clamp used to connect an earthing or bonding conductor to pipework. It carries a permanent label warning that it is a safety electrical connection.
The European standard for gravity drainage systems inside buildings. Like BS 7671 it does not size a cold water pipe, and like BS 7671 it is easy to pick up by mistake.
The European standard for verifiable backflow preventers with reduced pressure zone (family B type A), the standard a type BA RPZ valve is made to.
The British and European Standard method for calculating the design heat load of a building.
The European standard for the type AA air gap with unrestricted discharge, the standard BS 8515 cites for a rainwater back-up.
The European standard for the type AB air gap with non-circular (weir) overflow, the standard BS 8515 cites for a closed rainwater or greywater cistern.
The European standard for anti-pollution check valves, the standard single and double check valves are made to. BS 6282-1 was the older British Standard for the same devices.
The standard for radiators and convectors. It sets the test reference condition of 75 °C flow, 65 °C return and a 20 °C room, which is an excess of 50 K.
The European standard for drinking water installations inside buildings, in five parts: general, design (806-2), pipe sizing (806-3), installation (806-4, which includes pressure testing, flushing and disinfection) and operation and maintenance (806-5). It applies whatever the water source, so private supplies are designed and commissioned to it too.
The European standard for the design of drinking water installations inside buildings. Its clause 15.3.5.2 limits what a directly connected booster may do to the supply: when the pumps start the pressure must not fall more than 50 per cent below the lowest normal service pressure or below 100 kPa (1 bar), and when they stop the rise must not exceed 100 kPa above the permissible operating pressure.
The European standard for sizing pipework in drinking water installations. Its Table 2 gives the design flow rate and the minimum flow rate for each type of draw-off point, which measured flows are compared against.
The European standard for the installation of drinking water systems inside buildings. Its clause 6 covers commissioning: pressure testing (6.1), flushing (6.2) and disinfection (6.3).
The European standard for the operation and maintenance of drinking water installations. Its Table A.1 has an RPZ valve inspected every 6 months and maintained once a year, and Annex B forbids bypassing it.
An insulated vessel that adds a reservoir of heated water to a system, so the generator has somewhere to put its output and does not cycle.
The work another trade does so that the services can be installed: chases, holes, notches, ducts, bases and openings.
The local authority building control department, or an approved inspector, that checks building work complies with the Building Regulations. It must be told before work starts, by full plans or a building notice, inspects the work as it goes, and issues the completion certificate.
An officer of the local authority who checks plans and inspects work to ensure it complies with the Building Regulations.
The simpler way of notifying building control: a short notice with no plans, given before work starts, after which the work is inspected as it goes. It suits small jobs such as a new bathroom.
The statutory regulations covering the design and construction of buildings in England and Wales, enforced by building control. Their guidance is published as Approved Documents; Part G covers sanitation, hot water safety and water efficiency.
The law, separate from the Water Fittings Regulations, that sets standards for building work in England and Wales, enforced by the local authority. Part G covers sanitation, hot water safety and water efficiency; most work must be notified to a building control body before it starts unless it is self-certified by a competent person or is minor work listed in Schedule 2B.
The certificate given to the building owner or occupier confirming that self-certified work complies with the Building Regulations, usually issued by the competent person scheme operator.
The certificate issued for a completed installation stating that it complies with the Building Regulations, either by the building control body or by a competent person scheme member. It goes in the handover file with the water undertaker's acceptance and the commissioning records.
The engineer who designs the internal services of a building, such as heating, ventilation and hot and cold water supplies, including heat loss and heat gain calculations.
The document recording what is true of this particular building and job, such as its real construction, occupancy and hot water use. Standards supply generic figures; the specification supplies the specific ones.
A professional who advises on building and property matters, carries out building surveys, writes technical reports and checks that the Building Regulations are followed.
Work defined by regulation 3 of the Building Regulations, including the erection or extension of a building and the provision, extension or material alteration of a controlled service or fitting.
The person responsible for sourcing and purchasing the materials a contract needs, obtaining quotes for the quantities required together with delivery times and quality assurances.
A metal clip that holds a cable to a surface. Metal saddles or clips are used because non-metallic clips alone are not accepted as support.
The table that presents a pipe sizing calculation, with a row for each numbered section giving its loading units, design flow, pipe size, velocity, head loss, lengths, and available and residual head. It goes with a numbered line drawing so anyone can check the sizes line by line.
Checked against a known reference so that its readings can be trusted. A calibrated test gauge or test kit is the reference a fitted gauge, transducer or chlorine reading is compared with.
Checking and adjusting a test instrument against traceable reference standards, carried out by a calibration house and recorded on a certificate, not done by the operative.
A fitting on the end of the pipe feeding a storage tank that slows the incoming flow, so sediment is not disturbed and the water is not aerated.
The energy released by burning a stated quantity of fuel. Natural gas carries roughly 10.4 kWh per cubic metre, which is how a heat saving is converted into a fuel saving.
A vessel in which water is heated indirectly by a heat exchanger. The word is used in the standards for what is commonly called a hot water storage cylinder.
Sealing every open pipe end with a proper cap, blank or plug before leaving the job, however briefly, so that nothing can enter the pipework and no water escapes if the supply is restored. Rag pushed into the end, or a valve left slightly open, is not acceptable.
The employer's formal process for handling work that repeatedly falls below the required standard: written notice, a meeting, a decision and an appeal.
A component in a single-phase pump motor that stores an electrical charge and gives the motor the phase shift it needs to start and run. A failed capacitor is a common reason for a single-phase motor that hums or will not run.
Loss of a trap seal caused by a strand of hair or fibre lying over the weir of the trap, which draws the water out drop by drop.
A soldered joint in which solder is drawn into the gap between pipe and fitting. A dry joint is one where the solder has not run.
The one-off cost of buying and installing a system, as distinct from the cost of running it afterwards. Micro-renewable systems typically have a high capital cost and a low running cost.
The mass of carbon dioxide released per kilowatt-hour of a given fuel, used to compare systems fairly. Approved Document L 2021 (SAP 10.2) gives 0.210 kg per kWh for natural gas and 0.136 for grid electricity.
The activated charcoal element on a macerator's air valve that absorbs odours. It saturates in use and is replaced at the manufacturer's interval.
The replaceable fuse held in the carrier of a fused connection unit or plug. It protects the flex and the equipment beyond the accessory.
Two or more heat pumps of the same kind connected to work together on one system to meet a larger load.
In a galvanic cell, the more noble metal, which receives the current and is protected from corrosion — copper in contact with zinc or steel, for example.
The warning label placed at the point of isolation stating that the system is off and must not be switched on.
Vapour bubbles forming and collapsing in a pump, heard as a rattling noise; listened for during functional testing.
A system in which water is heated at one central point and distributed by pipework to all the hot outlets in the dwelling.
A pump in which a spinning impeller throws water outwards to raise its pressure. All booster pumps are this type.
The signed document an approved contractor must give the person who commissioned the work on completion, under Regulation 6, stating that the fittings comply with the Water Fittings Regulations. A copy goes to the water undertaker where the work was notifiable, and the owner keeps it as their statutory defence.
A watertight underground tank with an inlet and no outlet, used to store sewage until it is emptied by a licensed contractor. No treatment takes place.
The formal reporting line on a job showing who may give instructions and to whom problems are reported. Instructions travel down it and issues travel up it.
The documented route by which a proposed change is recorded, authorised and priced before it is carried out.
The pressure of the gas behind the diaphragm of an expansion vessel when there is no water in it, normally set to the pressure the system sits at when cold. Raising it reduces the expansion the vessel can accept.
The hourly rate a company charges for an operative's time, which is higher than the wage because it has to help carry the company's costs.
Filling every trap on the system with water before a test, so that no trap is an open path for air.
A valve that lets water flow one way only and closes against reverse flow. On a booster set one sits on each pump discharge; if the standby pump’s valve fails, water recirculates through the idle pump instead of reaching the outlets.
The Central Heating System Specification, CE51 2008, which sets out good practice and best practice packages of heating controls for domestic systems.
A durable label at an accessory or protective device stating what it supplies or isolates, as required by Regulation 537.2.7.
The conductor that connects the exposed metalwork of equipment on a circuit back to the main earthing terminal, so that a fault current can flow and the protective device can operate.
The pump that moves water round the heating circuits. Its duty is chosen from the pressure loss of the index circuit plus any pressure drop through the boiler.
The area free of obstruction required for access to an appliance without interfering with the users of other appliances.
The routine check of a stored-water cistern for cleanliness, contamination and general condition: annually, under BS 8558 clause 6.1.5.1, BS EN 806-5 clause 12 and HSE HSG274 Part 2, and sooner if fouling, debris or vermin are found. Not to be confused with the six-monthly sampling of stored drinking water in BS 8558 clause 6.1.4.1.
The flow the float-operated valve needs to refill a cistern in the required time: capacity divided by filling time in seconds. A dwelling's cistern should refill in under an hour (the withdrawn BS 6700's figure, still the usual one), up to four hours where nothing else is known (BS 8558); a 320 litre cistern in an hour needs 320 ÷ 3 600 = 0.09 l/s, which is added to the loading unit flow when the supply pipe is sized.
A cold water system in which a storage cistern, usually in the loft, feeds the outlets and the hot water cylinder through distributing pipes under the head the cistern gives. Also called an indirect system; the kitchen sink stays on the supply pipe so drinking water is wholesome.
The engineer who designs roads, bridges and tunnels serving a building, and is often involved in the drainage and water requirements to the site.
Equipment whose protection against electric shock relies on basic insulation plus a connection of its exposed metalwork to a protective conductor. A circulating pump is normally Class I.
A removable cap on a trap or fitting that gives access to clear a blockage without taking the whole trap off.
A chemical formulated for heating systems that lifts and disperses mineral oils, flux residues, sludge and scale so that flushing can carry them out.
A flush of an existing system after non-use, new components or possible contamination, as listed in PD 855468 clause 6.1.
The client's representative on site for quality. Checks and verifies the work as it is completed against the drawings and specification and keeps written records of sample checks.
Materials or appliances bought by the client rather than by the contractor. They are inspected, accepted or rejected in exactly the same way as the contractor's own.
A meter whose jaws clamp round one conductor to read the current flowing in it without breaking the circuit. A running current above the manufacturer’s figure points to loose connections, a shorted winding, burned starter contacts or a damaged pump.
A sealed circuit of buried pipe carrying a water and antifreeze mixture, which exchanges heat with the ground without taking any water from it.
Insulation whose cells are sealed from one another so it does not absorb water. It is used outdoors, with protection against ultraviolet light.
A screen on a stream intake that keeps out fish, weed, silt and debris, giving the supply its first protection.
A band of colour painted or taped on a pipe, about 150 mm long, at valves, junctions and where the pipe passes through walls and floors, to identify what it carries. The basic colour is shown either side of a code colour, so a reclaimed water pipe reads green, black, green.
A British or European Standard that recommends how work should be designed, installed or tested. BS EN 12056 and BS 8000-13 are codes of practice for drainage.
The ratio of useful heat delivered by a heat pump to the electrical energy it consumes at a given moment. A COP of 3 means three units of heat for one of electricity. A direct electric immersion has a COP of 1.
The pipe that drops from the feed and expansion cistern to fill the heating system and to allow expansion back into the cistern.
The pipe from the cold water storage cistern to the bottom of the hot water storage vessel. It supplies the cylinder only, and it is the route up which expanded water rises.
The pressure a sealed system is set to when it is cold, normally about 1 bar. It is read on the system pressure gauge.
Draining and emptying a filled system after the soundness test to carry out loose installation debris before the system is refilled.
A pressurised vessel that stores mains water when the supply pressure is at its highest and releases it during periods of demand, improving both flow and pressure.
The volume of cold water held in a cistern to cover peak demand and interruptions. BS EN 806-2 gives 80 litres per person for a dwelling with a constant supply, 130 litres per person where it refills only at night; the withdrawn BS 6700 set a 230 litre minimum for a cistern feeding both cold outlets and the cylinder, and at least the cylinder's capacity for one feeding the cylinder alone, still used as rules of thumb.
The open topped vessel that stores cold water above the outlets and feeds the hot water cylinder in a vented system. Its height gives the pressure at the taps.
The plan area of the roof or other surface drained to a rainwater harvesting system. It sets the ceiling on how much water the system can ever supply.
The buried pipework, in trenches or boreholes, through which a ground source heat pump absorbs heat from the ground.
A bath/shower mixer tap, made in pillar, deck, thermostatic and wall mounted patterns, requiring comparable hot and cold pressures.
A dual function appliance providing central heating and instantaneous hot water from one case, with no cylinder or cistern.
A cylinder with its own cold water cistern built on top as a single unit, with factory-fitted cold feed and vent. Known as a Fortic.
An instrument screwed onto an outlet that reads static pressure, running pressure and flow rate in one operation.
A thermal store with its own gas burner built in, heating the primary water directly so that no separate boiler is required.
A below ground drainage arrangement in which foul water and surface water are carried in the same sewer to the treatment works.
A single valve that acts on both temperature and pressure, used on most unvented vessels in place of a separate temperature relief valve.
The final stage of an installation in which the system is filled, tested, flushed, disinfected where needed, adjusted and checked for correct working before it is handed over, with the results recorded. Notice that commissioning is complete goes to building control and to the customer.
The written record completed at handover of the tests carried out, their results and the settings of the installed equipment. The dye test on a greywater or rainwater system is recorded on it.
The notice of completion of commissioning given to the building control body confirming that a fixed building service has been commissioned.
The written record of what a system did when it was first put to work: the type and duration of the pressure test, disinfectant concentration and contact time, flow rates and pressures at the outlets, pump suction and discharge pressures and the accumulator pre-charge. It is the baseline later faults are measured against and forms part of the system history.
A branch pipe serving more than one appliance before it reaches the stack. Traps on it are exposed to induced siphonage from the other appliances.
A calibrated test kit that changes colour with chlorine strength, used to read the residual (PD 855468 clause 10.1.6).
A floor built to a fire resistance rating that divides a building into separate fire compartments, for example the floor between two flats.
The relationship the compensator follows between outside air temperature and flow temperature. Set as low as the building allows and then proven in cold weather.
Having the training, knowledge, skill and experience to carry out a task safely and correctly. Authorisation is the separate question of whether you are permitted to.
A government-recognised scheme whose registered members can self-certify their own work as complying with the Building Regulations instead of notifying building control. For installing a wholesome cold water supply the listed schemes are APHC, BESCA, CORGI, NAPIT and NICEIC; the member gives the occupier a certificate within 30 days and notifies the building control body in the same time.
A scheme whose members certify their own building work, giving the occupier a certificate within 30 days and notifying building control themselves.
The certificate a building control body issues when notified work has been inspected and found to comply. For a new dwelling it cannot be issued until the water efficiency calculation has been received.
A single valve body containing several of the inlet control group components in their correct order, usually the strainer, pressure reducing valve, balanced cold take-off, check valve and expansion relief valve.
Loss of a trap seal caused by positive pressure. Water falling down a stack compresses the air below it and blows a low-level seal back up into the appliance. Also called back pressure.
A mechanical joint tightened onto an olive that grips the pipe. A missing olive is a classic visual-inspection find.
The pump that raises the pressure and temperature of the refrigerant vapour. It is the only part of the cycle that consumes electrical power.
Pipework that will be hidden by boxing, ducts, screeds or finishes. It must be inspected and tested before it is enclosed.
A 75 mm seal trap through which boiler condensate is discharged into sanitary pipework. The pipework must resist a pH of 6.5 and lower.
The heat exchanger in which the refrigerant gives up its heat to the heating water. Poor water flow through it raises the condensing pressure.
Maintenance triggered by measurements or inspections showing the condition of the plant, rather than by a fixed interval.
Requirements a water undertaker may attach when it consents to notifiable work, such as a particular backflow device or an inspection before pipework is covered. Regulation 5(1)(c) requires them to be complied with; breaching a condition is an offence like starting without consent.
A protective sleeve fitted over the pipe where it crosses a screed joint or threshold, so the two slabs can move without shearing the pipe.
The water undertaker's permission to start notifiable work. It has ten working days from the notice to consent, consent with conditions, refuse, or do nothing; if nothing is heard consent is treated as granted unconditionally, and it must not be withheld unreasonably.
The judged seriousness of an accident if it happens, scored from no injury or loss through first aid and lost-time injuries to fatality.
An area designated for its special architectural or historic character, where extra planning controls apply. Permitted development still applies there, with tighter conditions.
A man-made bed of wetland plants, such as a reed bed, that uses the plants' natural treatment capacity to polish septic tank effluent.
The principal health and safety regulations for construction work. They set duties for the client, principal designer, principal contractor, contractors and workers, and apply to all construction work including domestic work.
The contractor's main representative on site, responsible for its day-to-day running, including budgets, staffing, deliveries and progress.
The written plan setting out how health and safety will be managed during the construction phase, together with the site rules.
A card carried on site confirming that the holder has the training and qualifications claimed. Contracting customers normally require one before allowing access.
A component expected to be replaced at intervals through the life of an appliance, such as a macerator's carbon filter, rather than lasting the life of the unit.
The board at the origin of a domestic installation holding the main switch and the circuit protective devices for the final circuits.
The time the disinfectant is held in the system at its initial concentration. It starts only when the whole system, cisterns included, is filled at that concentration.
The period the chlorinated water is left in the system, at least one hour from when the whole system is at 50 mg/l, longer at high pH.
Any reduction in the chemical or biological quality of the water, whether by a change of temperature or by a polluting substance getting into it (Schedule 2 paragraph 1). Backflow from a hose left in a bucket of disinfectant is the classic example; a change that only affects taste, such as softening, is not contamination.
A plan prepared in advance for a foreseeable problem, so that work can continue with the least loss of time and money when it happens.
A measurement of resistance proving there is an unbroken low-resistance path along every protective and bonding conductor back to the main earthing terminal.
Having enough uninterrupted work available for the gang to keep going once they have started, rather than stopping and returning.
A measurement of resistance along a conductor to prove it is unbroken. It is used to find an open circuit and is carried out dead.
The agreement between the parties setting out the work to be done, the price, the time allowed and how changes will be handled.
The person named in a construction contract to administer it on the client's behalf, including issuing instructions and valuing changes. Often the architect.
The overall schedule for a contract, showing when each part of the work must be done and the target completion dates.
A business or organisation that engages a plumbing firm under a contract to carry out work for it. On a construction site this is normally the main contractor.
The manager who supervises the creation and management of building contracts, liaising between head office staff and the site agents.
The power to instruct a change to the contract. It rests with the paying customer on a private job, or with the person the contract names, such as the architect or contract administrator.
The electronic controller on a small packaged booster set that reads the transducer, starts and stops the pump and may vary its speed to hold the pressure steady.
Anything put in place to remove a hazard or reduce the risk from it, such as a guard, a barrier, a safe system of work or protective equipment.
Regulations requiring employers to assess the risk from hazardous substances and to prevent or adequately control exposure to them.
The electrical panel on a booster set that starts and stops the pumps in sequence from the transducer or switch signals.
The thermostat that holds the stored water at its working temperature of 60 to 65 degrees C. On a direct system it is the immersion heater thermostat; on an indirect system it is the cylinder thermostat.
A service or fitting subject to the Building Regulations, such as drainage, sanitary pipework, hot water or heating equipment. Providing or altering one is building work.
Heat carried by moving air. Cool air is drawn in under the radiator, warmed by the fins and rises off the top as a warm current.
A deliberately uninsulated length of pipework, typically on the connection to the expansion vessel, that lets hot fluid and vapour lose heat before reaching a temperature-sensitive component.
The multiplier that converts a radiator's catalogue output at the reference condition to its output at the actual mean water temperature and room temperature. Catalogue output equals heat loss divided by the factor.
Work done to put right a fault that has been identified, before or after it causes a failure.
The chemical left permanently in the system water to minimise corrosion of the metals and to inhibit the formation of magnetite sludge and limescale.
The Control of Substances Hazardous to Health Regulations, which govern the use of chemicals such as descaling acids on site.
A contract under which the contractor is reimbursed the actual cost of labour, materials and plant, plus an agreed fee or percentage.
The short letter or email sent with a quotation, saying what is attached, what it covers, the price and timing, and how to respond.
The slow stretching of plastics pipe under sustained pressure, largest at first and tailing off as the material settles into its new shape.
The highest level water can reach in a cistern with the float-operated valve failed fully open and the overflow or weir running at full bore. A type AG or AB air gap is measured down to this level, not to the normal water line.
The chain of dependent activities that determines the total duration of a project. Delay to any activity on it delays the whole job.
A way of programming work that identifies the chain of activities determining the total duration of the project, so delay to any of them delays the whole job.
A physical link between wholesome water and water that is not wholesome: rainwater, greywater, a private supply, a heating circuit or the hot side of a mixer. Under Schedule 2 paragraph 14 the connection itself is an offence, whether or not anything flows through it; a closed valve or a hose dropped into a tank is still a connection.
Any pipe or fitting that could let water from another source, such as a private supply, rainwater, greywater or a heating system, reach the wholesome mains supply. Schedule 2 paragraph 14 forbids it outright and requires non-wholesome pipework to be clearly identified; it is the one rule that applies even to private supplies.
The accidental connection or backflow that lets non-potable water enter a wholesome water supply. It is the principal health risk of any re-use system, and is guarded against by air gaps, marking and testing for cross-connections.
The discharge from one branch pipe crossing the stack and entering another branch, instead of falling down the stack.
The area of the copper in a conductor, quoted in square millimetres. It determines how much current the conductor can carry and how much it will drop in voltage.
Discharge from one branch pipe flowing across the stack and into the opening of another branch opposite, instead of down the stack.
The chemical hardening of a screed after it is poured, which takes time and depends on the screed keeping its moisture. Heat must not be used to speed it up.
The two settings on a pressure switch: cut-in is the falling pressure at which the pump starts, cut-out the rising pressure at which it stops. Both are checked against a calibrated gauge and the commissioning figures.
The pressure at which the low pressure switch starts the pumps as water is drawn.
A ditch dug upslope of a spring chamber to carry surface run-off around it instead of into it.
The pressure at which the high pressure switch stops the pumps once the system is up to pressure.
A full-size pattern supplied by a manufacturer to mark out a cut-out, for example the hole in a worktop for a countertop wash basin.
Repeated short runs and stops of a heat source, caused by reaching setpoint too quickly. It wastes energy and wears components.
The control that senses stored water temperature and switches the heat source off at the set temperature. It provides normal operating control, not safety.
The short metal pipe from the relief valve to the tundish, no smaller than the valve outlet and no longer than 600 mm.
The pipe from the tundish to the point of discharge, at least one size larger than the valve outlet, with 300 mm of vertical pipe before any bend and a continuous fall thereafter.
The volume of hot water a design assumes each occupant uses in a day, quoted at a stated temperature. Around 45 litres per person per day at 60 degrees is the usual mixed-use figure.
The words of Regulation 3(3): a fitting in that condition which is likely to cause one of the five harms must not be used. It is the rule that makes the owner or occupier responsible for maintaining fittings, not just the installer for fitting them.
The sheet layer in a ground floor that stops moisture rising from the ground. In an underfloor build-up the insulation sits above it.
The plate on a pump or motor giving its rated duty, pressure, current and voltage. Readings taken in service are compared with the data plate figures.
The zero reading taken on the manometer before pressure is applied. Every later reading is compared against it.
A record of the hours, materials and plant used on work that is charged at agreed rates rather than being covered by the contract price. It is only worth anything if the work was instructed.
A sound level in decibels, weighted to match how human hearing responds. MCS 020 a) sets the domestic heat pump limit at 37 dB LAeq,5mins, the A-weighted level averaged over five minutes.
The purpose-made tool supplied with a disposal unit for freeing the grinding blades. It is only used with the supply safely isolated.
A length of pipe in which water does not move because the outlet it serves is rarely or never used. Stagnant water in it can warm, lose its chlorine and grow bacteria, so dead legs are avoided in design; where one is unavoidable a single check valve stops it feeding back.
The permanent weight a structure carries, including its own materials and anything fixed to it such as collectors and their mountings.
A test carried out with the circuit isolated and proved dead. Continuity, insulation resistance and polarity are all dead tests.
Transferring a substance from its original container into another. It must never be done into an unmarked container, because the hazard information is lost.
Taking a component or section out of service safely: relieving the pressure, draining with air admitted, capping the open ends and disconnecting it. Where something is removed for good, the pipe is cut back to the live main to avoid a dead leg.
A circuit run from the consumer unit that supplies one item of equipment or one system only, with its own protective device.
Any failure found during commissioning, from a leak to a wrong component, corrected immediately and retested before further work proceeds.
Work that does not meet the specified standard and has to be taken out and redone, delaying everything that depends on it.
The period after practical completion during which the building is in use and any agreed or newly emerged defects are put right, usually before final payment is released.
In work performance, a problem that affects safety, quality or cost effectiveness, such as incorrectly specified pipework or unsafe installation.
The operation in which an air source unit reverses its cycle to melt ice off the outdoor coil. It must start and stop correctly and the meltwater must drain away.
An inlet valve that stays shut until the cistern level falls to a pre-set point, then opens fully for a fast fill. The Keraflo or Aylesbury type.
A control function that compares actual room temperature with the temperature required at the programmed start time and delays firing the boiler if the house is already close.
The sharing or transfer of authority and responsibility from an employer or supervisor to an employee for a particular task.
The temperature hot water is actually used at, taken as 45 degrees for design. It is lower than the storage temperature because water is blended at the outlet.
A document listing the type and quantity of materials delivered to site. It is checked against the goods and signed only if the two agree.
The part of handover in which the customer is walked round the system, shown how the controls work and how to isolate the supply, and allowed to do it themselves.
A link between two activities on a programme, where one cannot start or finish until the other has reached a certain point.
The vertical depth of water held in a trap, measured in millimetres. Approved Document H requires at least 25 mm to be retained under working and test conditions.
A factor supplied by the pipe manufacturer, applied to the test pressure when the equilibrium temperature of a plastics pipe system is above 25 degrees C.
Removing lime scale from pipework, usually with a diluted, inhibited acid-based fluid applied at set points or by drip feed, followed by thorough flushing with clean water.
The record of what the customer wants from the system: rooms heated, temperatures, running hours, hot water demand and budget. It is agreed before calculation begins.
The drawing showing what was intended; often overtaken on site and not the drawing handed over.
The person responsible for the design and pipe sizes, consulted when flow or pressure falls short because the pipes look too small.
The flow rate a circuit was designed to receive. A circuit that is not getting it will underperform however good the heat source is.
The flow an outlet should receive when it is the only one discharging, in litres per second. BS EN 806-3 Table 2 gives 0.1 l/s for a basin or WC cistern, 0.2 l/s for a sink or shower, 0.3 l/s for a urinal flush valve, 0.4 l/s for a bath and 0.5 l/s for a garden tap.
The temperature the system is designed to send to the emitters at the design condition. It sets the emitter sizes and, on a heat pump, largely sets the running cost.
The total heat a building needs at the design condition: the sum of the design heat losses of every heated space plus the capacity needed to warm up after an off period. It sizes the heat generator.
The total heat a room or building loses at the design condition, being fabric loss plus ventilation loss, before any allowance for warm-up is added.
The temperature the water is designed to arrive back at the generator. Keeping it below about 55 °C is what allows a gas condensing boiler to condense.
The intended difference between the flow and return water temperatures at design conditions. BS EN 12828 gives 10 °C for a conventional system.
A large-scale drawing, at 1:20, 1:10 or 1:5, of one part of a building such as a bathroom or plant area, showing what a floor plan is too small to show. Also called a part plan.
The temperature at which vapour in a gas begins to condense. Natural gas flue products have a dew point around 55 °C, which is the basis of the condensing boiler return limit.
The corrosion of ordinary brass in which the zinc is leached out, leaving a weak, porous, reddish copper skeleton that cracks. It shows as a white powdery zinc oxide on the fitting.
Dezincification is the corrosion of ordinary brass in which the zinc leaches out and leaves a porous copper skeleton that keeps its shape, shows no symptom and then fails suddenly. Dezincification-resistant (DZR) brass is an alloy treated so that it does not do this, proved by the BS EN ISO 6509 test and marked CR or DRA; exam answers quote a resistant depth of at least 200 microns.
Brass alloyed and heat-treated so that it does not lose its zinc in aggressive water. Grade A dezincification-resistant fittings are marked CR (corrosion resistant) or DRA, and CR is the marking to look for.
The process of working from the symptoms and the evidence to the actual cause of a fault, and proving that cause before anything is replaced.
Measurements taken on a working system — pressures, flow rates, currents, resistances — and compared with the commissioning record and the manufacturer’s data, so that the fault is located by the difference rather than by guesswork.
A flow chart in the manufacturer’s operation and maintenance instructions that leads you through a fault step by step, each box asking one question and the chart starting with the cheapest and most likely cause.
The flexible membrane or bladder that separates the water from the gas charge inside an expansion vessel. If it ruptures the vessel waterlogs and can no longer take up expansion.
An expansion vessel in which a diaphragm separates the water from the gas charge, with the water lying against the steel shell. Used on sealed heating systems, not on unvented hot water.
The difference between two pressure readings, for example across the first check valve of an RPZ valve. RPZ testing records the static, dynamic and differential pressures at the three test points.
A valve that regulates the pressure difference across the manifold so that circuit flow rates stay as set when other circuits open and close.
The valve between the two check valves of an RPZ valve, held shut by supply pressure. If supply pressure falls to within about 0.14 bar of the zone pressure, or the zone pressure rises because a check valve leaks, it opens and dumps the zone to drain; a steady discharge from the relief port shows the first check valve is leaking.
The control that compares the collector temperature with the cylinder temperature and runs the solar circulating pump only while the collector is hotter.
A valve on the manifold that automatically regulates pressure changes within it, so setting one loop does not disturb the flow rates already set on the others.
Solar radiation scattered by cloud, dust and water vapour, which appears to come from the whole sky. About half the UK annual total.
A fitting on the cold feed inside a storage vessel that spreads the incoming cold water gently across the base, so that it does not jet upwards and mix the temperature layers.
A shower whose temperature and flow are set on an electronic control panel and held by a remote processor operating proportioning valves or a motorised mixing valve.
A thin rule, usually matt black, lowered into a trap to measure the depth of water seal remaining. The wetted length is read off it.
Pumps fitted straight on to the incoming supply pipe so they draw on the main. Allowed only below 0.2 l/s or with the water supplier consenting.
A hot water storage vessel with no heat exchanger, in which the stored water is heated directly by an immersion heater or by circulation through a boiler.
Distribution in which harvested water is pumped from the storage tank straight to the points of use, with the control unit introducing mains water when needed.
Solar radiation arriving straight from the sun without being scattered.
Supervision in which a competent person is present and watching the work, used where a task is new to the worker, the risk is high, or the worker is inexperienced.
A cold water system where the incoming supply pressure serves the outlets without a storage cistern.
A storage vessel heated by its own burner with factory-fitted controls, rather than by a separate boiler. Mostly used in commercial work.
The pipe from the tundish of an unvented cylinder that carries any discharge from the safety valves to a safe outside position. Its route is often what decides where the cylinder can go.
The short metal pipe from a safety device to the tundish. It must be at least the nominal outlet size of the valve it serves.
The pipe from the tundish to a safe outside termination. It falls continuously and is sized up from the valve outlet according to its equivalent resistance length.
The vertical pipe that receives branch discharge pipes and carries the flow to the drain. In a primary ventilated system it also ventilates the pipework, which is why it is called a soil and vent pipe.
The design load figure given to each sanitary appliance in BS EN 12056-2 Table 2. Discharge units are added up and converted to a flow rate to size branches and stacks.
Something on site that does not match the drawings or tolerances, such as an out-of-position opening or an out-of-tolerance substrate. It must be reported before any further work is done on it.
Dosing a new, altered or contaminated water installation with a chemical, normally chlorine, and leaving it in contact for a set time to kill micro-organisms, then flushing it out. BS EN 806-4 sets the method and requires the water supplier to be told beforehand where the chemical could reach the point of delivery.
A small storage water heater in which incoming cold water pushes the stored hot water out of the outlet. Over sink and under sink heaters work this way.
A pipe carrying water from a storage cistern to the outlets it serves, under the head given by the cistern rather than mains pressure. Rainwater and greywater systems must have their own dedicated distributing pipework.
The company that owns and operates the local electricity cables and network. Supply upgrades and reinforcement are agreed with the DNO, not with the energy supplier.
The temperature at which hot water travels through the pipework to the outlets. It must bring every outlet to at least 50 degrees C within one minute (55 degrees C in healthcare).
A perforated or spreading pipe fitted to a downpipe shoe so that discharge onto a lower roof spreads across a wide enough flow width not to over-top the receiving gutter.
The allowance made in a maximum demand calculation for the fact that not all connected equipment operates at full load simultaneously.
The valve inside a combi boiler that redirects primary water to the domestic hot water heat exchanger when a hot tap is opened.
Nominal diameter, the size designation used in BS EN 806-4 to decide which test procedure a combined metal and plastics system uses; DN 63 is the boundary.
Nominal diameter expressed by outside diameter. BS EN 806-4 uses DN/OD 63 as the dividing size for choosing between test procedures on plastics systems.
The label fixed to every valve and isolator you have closed while work is in progress, saying the system is off and must not be turned on, with the name and telephone number of the person to contact. Only the person who fitted it removes it, and only when the work is finished.
All the written evidence of what a system has already had done to it: commissioning records, maintenance logs, service reports and as-fitted drawings.
The guidance document that sets the minimum standards for efficiency, controls, zoning, insulation and commissioning of domestic heating and hot water systems.
A person for whom a construction project is carried out that is not in connection with a business. Their client duties normally pass to the contractor or principal contractor.
The supporting guidance for Approved Document L1, setting out how domestic heating and hot water systems should be specified and commissioned to comply.
A method of fixing plasterboard to blockwork on dabs of adhesive, leaving a void behind the board that fixings must bridge.
Two check valves in one body giving backflow protection against a fluid category 3 risk, fitted on the hot and cold to a mixer with a hose.
A switch that breaks both the line and the neutral conductor. It contains no fuse, so it is used only on circuits that are already correctly rated and dedicated.
Emptying a system, or a section of it, through the drain taps, with the draw-offs above opened so that air can enter to replace the water.
A small valve with a hose connection at the low point of a pipe run, cistern, cylinder or vessel, used to empty that section. Pipework downstream of a stopvalve should fall continuously towards one so that nothing is left standing.
A system in which the collector automatically empties into a vessel when the pump stops, protecting it from freezing and from stagnation.
A valve at a low point for emptying the system; the customer is shown where it is but it needs no operating instructions.
A system of sub-surface irrigation pipes that lets septic tank effluent percolate into the soil, where biological treatment takes place in the aerated layers.
A small tap fitted at the low points of a system so it can be emptied. It should be a screwdown type to BS 2879, or an approved spherical (ball) type only where it cannot freeze, and must not have a loose washer plate that could lodge in the seat and stop it shutting.
The pipe taking hot water from the top of the storage vessel to the outlets. It rises from the cylinder rather than falling, because the hottest water is at the top.
Any outlet from which water is drawn: a tap, shower, WC cistern inlet or appliance valve. Pipe sizing starts at the last draw-off point on a run and works back towards the source.
A standard mark used on a drawing to represent a component such as a cistern, valve, pump or vessel, so the drawing can be read by anyone. BS 8558 Table 2 lists the symbols for water services.
A pipe high in a building, filled by direct boosting, holding 5 to 7 litres per dwelling of drinking water for the sinks while the pumps are off.
The body that approves substances and products used in contact with drinking water, including disinfection chemicals, under the water quality regulations.
The list a disinfectant must appear on for use in public water supply (PD 855468 clause 4.10).
A pressure reducing valve that holds its reduced pressure with no flow, so the downstream pressure cannot creep up.
A flushing device sealed by a mechanical flap or seat that lifts to release the flush. It operates easily and gives a dual flush, but it can leak quietly into the pan.
A pump running with no water in it. It overheats and destroys its seals within minutes, so a low-level float switch stops the pumps when the cistern empties.
A low-level float switch in a break cistern that stops the pumps when the water falls too low, so they cannot run dry.
A WC cistern with two flush volumes, a full one and a smaller one for liquids. Schedule 2 paragraph 25 limits the full flush to 6 litres and the smaller flush to no more than two-thirds of it, so the largest dual flush allowed is 6 and 4 litres.
A high grade stainless steel with a mixed structure giving high strength and good corrosion resistance, used for most modern unvented cylinders.
Two or more pumps in parallel on a booster set, sized so peak demand is met with one pump out of action, with the lead pump rotated.
The length of time an activity occupies on the programme, read from the length of its bar.
A space carrying airborne fibres, lint or dust, such as a laundry or workshop. Air admittance valves must not be used in one because the inlet clogs.
The arrangement on a booster set where one pump (the duty) runs to meet demand and the second (the standby) waits to take over on failure or at peak load. The control panel should alternate the duty so that neither pump stands idle and its water stagnates.
The person responsible for a non-domestic building's water hygiene under ACOP L8, who keeps the Legionella records.
The legal duty on anyone producing or handling waste to keep it secure, transfer it only to an authorised person and describe it in writing.
The combination of flow rate and head a pump must deliver for a particular system. It is plotted on the pump chart and a curve on or above it is selected.
A test for cross connection: dye is put into the non-wholesome system before it is connected to the mains back-up, and every wholesome outlet is run and checked to be clear. Required by BS 8525-1 before handover; the water undertaker may ask to witness it.
The pressure while water is being drawn, always lower than static because of friction loss; the pressure the outlets actually feel.
The continuous assessment made by a competent worker while the job is under way, checking that what is actually found still matches what was assessed and planned.
Dezincification-resistant brass, an alloy treated so the zinc is not leached out of it by aggressive water, which would leave the fitting porous and weak. Check valves and other backflow devices are made from it.
The total impedance of the path a fault current takes from the point of fault back through the supply. Measured live, and recorded on the certificate as Zs.
The conductor joining the main earthing terminal of an installation to the means of earthing, such as the distributor's earthing terminal at the cut-out.
Keeping the electrical earth path unbroken through metal pipework. When a length of metal pipe is cut out for repair, a temporary bonding lead is fitted across the gap, and BS EN 806-5 clause 10 requires the continuity to be maintained across the repair.
The lever or twist top fitted to a relief valve so that it can be opened by hand for testing. Operating it proves the valve is free and will re-seat.
A gutter fixed along the lower edge of a roof slope, the ordinary domestic arrangement. Valley and parapet gutters sit within or behind the roof and are designed to stricter rules.
The part of ErP that places minimum energy efficiency requirements on manufacturers, so that appliances placed on the market meet a defined standard.
The strip of insulation placed round the perimeter of a heated screed before it is poured. BS EN 1264-4 calls it the peripheral insulating strip.
The actual length of a pipe run plus an allowance, usually about 33 per cent, for the resistance of fittings and changes of direction. It is used to calculate section resistance.
The actual measured pipe length plus the equivalent length of all the valves and fittings on that section.
The area a gutter must be designed to drain: the plan area of the roof corrected for its pitch, with any wall or surface draining onto it added. It is larger than the measured plan area on a pitched roof.
A plastics pipe material such as PVC-U or PVC-C, and multilayer pipe, that expands under pressure but recovers, sitting between metals and visco-elastic plastics in behaviour.
The BS 7671 model form issued for a new installation, or for an addition or alteration that includes a new circuit or a new consumer unit. Schedules of inspection and test results are issued with it.
The report produced after periodic inspection and testing of an existing installation. It reports on condition and is not used to certify new work.
Regulations requiring electrical systems to be maintained safe, work on them to be done by competent people with effective isolation, and live work to be avoided.
The statutory regulations covering electrical safety at work. They require conductors to be made dead before work where reasonably practicable, and live work only with justification and precautions.
A list of metals in order of their electrode potential, from noble metals such as copper (+0.15 V) to reactive ones such as zinc (−0.76 V). The further apart two metals sit in the series, the faster the less noble one corrodes when they are joined.
A liquid that conducts electricity because it contains dissolved ions. Water, especially hard or salty water, is an electrolyte, which is what lets galvanic corrosion take place between dissimilar metals.
Corrosion that happens when two different metals are in electrical contact with water (an electrolyte) between them. A small current flows; the less noble metal (the anode) is eaten away and the more noble metal (the cathode) is unharmed.
The area of one part of the fabric, such as a wall, window or floor, used in the U times A times delta T calculation. Wall areas are taken net of openings.
A drawing of one face of a building seen from the side, so it shows heights: of a storey, an eaves or a cistern platform. It does not show pipe runs under the floor, the room layout or the drains.
The area of a surface as seen from the side, used for walls and for roofs pitched over 70 degrees. Half of it is taken as the effective catchment.
Removing the hazard from the job altogether, for example by prefabricating off site so that hot work is not needed at all.
The planned response to a foreseeable emergency on the job, such as rescue from an excavation, first aid, spill response, evacuation and who to call.
Shutting off the water supply at the stop valve or isolating valves when a pipe bursts; the customer is shown where the valves are and how to operate them.
The radiator, fan convector or underfloor circuit that gives the heat out into the room. Emitters sized for a boiler are usually too small for heat pump flow temperatures.
The written list of every room, its design heat loss and the emitter selected to meet it. It is a design document produced by the designer, not a source of data.
The case or box that contains live parts and terminations, providing basic protection against contact and mechanical protection for the connections inside.
The person who uses the water system day to day — the householder, tenant, caretaker or building manager. In fault finding they are the first source of information, because they can describe when the fault started, how it shows itself and what they have already tried.
A non-self-resetting device that disconnects the supply of heat to the storage vessel if the system overheats. It has to be reset by hand, and a trip means something is wrong.
The published assessment of a dwelling's energy performance. Installing a micro-renewable system generally improves it, which is one of the benefits a customer values.
The framework, effective from 26 September 2015, that sets efficiency levels for energy using products through Ecodesign requirements and an A to G energy label.
The company that sells electricity to the customer and issues the bill. It owns none of the network equipment.
A notice served on a building owner requiring work that does not comply with the Building Regulations to be put right.
A physical measure designed into the work to protect people, such as a guard, a trench support, local extraction or a working platform.
Energy Networks Association documents governing the connection of small and larger generation to the distribution network. They apply to generation, not to demand.
Expanded polystyrene insulation. Cheaper than PIR but needs greater thickness for the same U-value, typically about 110 mm in a ground floor.
A float valve with a hole through its piston so inlet pressure acts on both sides; the float only lifts the arm, which suits high-pressure inlets and reduces hammer.
The resistance of bends and fittings expressed as an extra length of straight pipe, added to the actual run when sizing a discharge pipe.
The length of straight pipe that would cause the same head loss as a fitting such as a bend, tee or valve. Added to the measured pipe length to give the effective length used in the head loss calculation.
The length of straight pipe that would cause the same pressure loss as a valve or fitting. Adding it to the measured length gives the effective length used for sizing.
The energy label supplied with a product so consumers can compare efficiency consistently. It shows an efficiency class alongside data such as rated output and sound power level.
One of the five harms: anything that stops the water meter recording the amount of water that actually passed through it, such as a pipe connected so that it bypasses the meter.
Passing a fault to the manufacturer or a specialist because it is beyond your competence or your authorisation to deal with.
A flange fitted in the side of a hot water cylinder to draw hot water for a shower pump below the air at the top, so the pump does not draw air.
An approximate price for a piece of work that can change as the job proceeds, unlike a quotation, which is fixed. On larger jobs it is produced from the bill of quantities.
The person who prices work before it is carried out, breaking the bill of quantities into labour, materials and plant, applying rates and adding overheads and profit.
A glycol used as an antifreeze and heat transfer fluid. It is considerably more toxic if swallowed than propylene glycol.
A collector made from double-walled glass tubes with the air evacuated, which almost eliminates conduction and convection losses.
Loss of a trap seal by the water drying away when the appliance is not used. BS EN 12056-2 ND.2.5 warns that infrequent use can give total loss of seal.
The heat exchanger where the refrigerant boils and absorbs low-grade heat from the air, ground or water.
The finned coil in an air source unit through which outside air passes and from which the refrigerant absorbs heat.
The part of a written quotation that lists what the price does not cover. Anything not named there is normally the contractor's cost if it turns out to be needed.
A heat pump that recovers heat from the warm, stale ventilation air being extracted from a dwelling. Its output is capped by the ventilation rate, so it suits small, airtight properties.
The controls already in place before the assessment is made, recorded on the form so that the further action needed can be judged against them.
A valve on the cold supply close to the vessel that discharges water if the pressure rises above its setting, for example when the expansion vessel has failed.
The proportion by which the water in a system increases in volume between its fill temperature and its maximum operating temperature, written as e in the vessel sizing formula.
A pressure activated valve that releases expansion water if the expansion vessel or bubble fails, or if the supply pressure becomes excessive. It is listed with the functional controls, but its job is safety; it is not one of the two safety devices Approved Document G requires.
A pressure-operated relief valve on the cold inlet of an unvented cylinder. It opens when system pressure rises above its setting, which happens if the expansion vessel or the pressure reducing valve fails. Also called the expansion relief valve or pressure relief valve.
The vessel on an unvented hot water system that takes up the expansion of heated water, sized on the volume heated and the operating pressure at not less than 4 per cent.
An addition of about ten per cent to a calculated heat loss where the building is on an exposed site, to cover severe weather.
How sheltered or open a building's location is. Exposed coastal, high altitude and rural sites use a lower external design temperature and may carry an extra percentage allowance.
The realistic low outside temperature the system is designed against, taken as a regional figure from published data rather than the coldest ever recorded.
The conditions a wiring system has to withstand where it is installed, such as heat, water, impact, vibration and sunlight. The cable and its protection are chosen to suit them.
A covered storage cistern outside the house on a private supply, from which a booster set pumps into the building. Insulated, lockable and screened.
A conductive part that is not part of the electrical installation but is liable to introduce a potential, such as incoming metal water or gas pipework. It is bonded, not earthed as a protective conductor.
The law controlling fluorinated greenhouse gases used as refrigerants. Deliberate release is prohibited and recovery must be recorded.
The qualification required to work on sealed refrigerant circuits containing fluorinated greenhouse gases. Without it, an operative must not break into the circuit or adjust the charge.
The regulations controlling work on fluorinated refrigerant circuits. Anyone brazing, pressure testing, evacuating or charging a refrigerant circuit on site must hold a relevant handling qualification.
The principle that reducing a building's heat loss by insulation and sealing is cheaper and more permanent than buying extra heat generator capacity to replace the lost heat.
Heat conducted out through the building structure. It is calculated element by element as U multiplied by area multiplied by the temperature difference.
The gradient given to a near-horizontal discharge pipe, so it drains completely at a self-cleansing velocity. Usually expressed as a ratio or as millimetres of fall per metre.
A number or letter sequence shown on a display to indicate which protection or check has operated. Codes are specific to the manufacturer and model.
The process of working from reported symptoms and observed evidence to the actual cause of a fault, before any repair is attempted.
A step-by-step decision tree supplied by a manufacturer. Each step asks a question that can be answered yes or no and directs you to the next test or to the cause.
The flow chart in a manufacturer's instructions that leads from a symptom to a likely cause and a check to make.
A manufacturer's diagnostic chart that works through a fault by symptom, each yes or no answer leading to the next check. It is the first reference for a pumped or powered sanitary component.
The small cistern that fills a vented primary circuit and accepts its expansion. It is separate from the cold water storage cistern in a double feed system.
A small metal tube crimped onto the end of a fine-stranded conductor so the strands cannot spread or separate in a screw terminal.
The proportion of a vertical rainwater pipe's cross-section occupied by water. BS EN 12056-3 uses 0.33 unless national practice sets another value between 0.20 and 0.33.
A temporary flexible connection between the supply pipe and a sealed heating system used to fill or top it up. It carries a double check valve on the supply side, never the heating side, and is disconnected after use. It is accepted on a house system; the withdrawn BS 6700 also allowed it on a non-domestic system under 40 kW.
A small tool used to straighten bent fins on a coil so that airflow through it is restored.
The statement prepared at the end of a contract, showing the total value of the work carried out and the final sum due.
The second balance of the loops, carried out once the building is furnished and has been running at design temperature for at least a week, because floor coverings change each loop's output.
A circuit connected directly to current-using equipment or to socket outlets, taken from a distribution board or consumer unit.
The check made on completion of a discharge system, before testing, to confirm the standard has been followed and that nothing has been left in or projecting into the pipes.
The soundness test on the whole installation at completion, required by the Regulations and recorded on the commissioning record.
A conductor made of many very thin strands, as used in flexible cable. It needs a suitable terminal or a treated end so that the strands cannot spread.
The raised guard on a test probe that stops a hand sliding forward onto the live conductor being tested.
A part of a building enclosed by fire-resisting walls and floors, designed to contain a fire. Services passing through a compartment line must be properly fire sealed.
Sealing an opening or gap in a fire separating wall or floor so that fire and smoke cannot pass through it for the required period.
The stage of work before the building is closed in and finished, when wiring, pipework and fixings go in and positions are agreed.
A contract where the price is agreed before the work starts and does not vary unless the work itself is varied by agreement.
Equipment secured in place and connected permanently to the fixed wiring, such as a boiler, a pump or a controller. It is not supplied through a plug and socket.
The bolted or screwed union connection each side of a circulating pump. The joint is sealed with a flat rubber washer.
A glazed, insulated collector with an essentially flat absorber plate and no concentration of the radiation.
Cable whose conductors are made of many fine strands so that it can be bent repeatedly without fracturing. Used for connections to pumps, valves and appliances.
The spare time available to an activity: the amount by which it can be delayed without affecting the completion date.
A switch that rises and falls with the water level and makes or breaks an electrical circuit, used to start and stop pumps or signal a valve.
The ordinary float valve in which a float and lever close a washer on a seat. Restrictive and slow on a large cistern.
A draw-off that floats about 100 to 150 mm below the water surface, taking water from the cleanest part of the tank.
An underfloor construction where grooved structural insulation panels are laid loose on the sub-floor, with a transfer plate and pipe in the groove and the finish over the top.
The level to which foul water would rise in a blocked system, taken at the highest appliance served. An air admittance valve is always fitted above it.
The thermal resistance added by carpet, timber, tile or vinyl over a heated floor. The design assumes a particular covering, and changing it changes the output.
The weight a floor has to carry at a given point. For a cylinder it is the vessel plus its full contents, reckoned at roughly one kilogram per litre.
A plan of one floor of a building, usually at 1:100 or 1:50, showing the room layout, wall thicknesses, appliance positions and horizontal pipe runs. With the bill of quantities it is used to work out the cost of a job before it starts.
A valve with an interchangeable cartridge that passes a set flow, between about 0.07 and 0.43 l/s, regardless of the pressure upstream.
A sight gauge on the flow bar of an underfloor manifold that shows the flow rate through one circuit, usually in litres per minute.
The pressure at an outlet while water is flowing, always lower than the static pressure because of friction in the pipe. BS EN 806-3 requires at least 100 kPa (1 bar) at a draw-off point; also called dynamic or running pressure.
The mass or volume of water passing a point each second, in kilograms or litres per second. It is found from the heat duty and the design temperature difference.
A small fitting that limits the rate at which water can pass through a tap or inlet. It saves water only on fittings that consume in proportion to flow, such as taps and showers; a WC uses a fixed volume per flush, so restricting its inlet saves nothing.
A sensor in a packaged set control box that stops the pump if no water is passing, protecting a submersible in a dry borehole.
A switch operated by water moving through it. Found on some small direct-boosting pumps and on shower pumps, but not the normal control on a boosted private supply.
The temperature of the water leaving the heat pump to the emitters. Heat pumps are designed for low flow temperatures, typically around 35 to 45 °C.
The speed of the water along the pipe in metres per second. BS EN 806-3 bases its tables on 2.0 m/s in distribution and rising pipes and 4.0 m/s in a connection to a single fitting (the withdrawn BS 6700 allowed 3 m/s); it is kept low mainly to limit noise, and also erosion of the pipe wall.
A regulating valve with a built-in flow indicator, so the circuit can be set directly to a flow rate in litres per minute instead of being inferred from temperatures.
Schedule 1 of the Water Fittings Regulations grades water by the harm it could do if it flowed back into the supply: category 1 is wholesome mains water, 2 has only its aesthetic quality changed (hot or softened water), 3 is a slight health hazard (low-toxicity substances such as glycol or disinfectant), 4 a significant hazard (toxic substances such as pesticides) and 5 a serious hazard (pathogens, faecal matter, radioactive or very toxic substances). Backflow protection must match the highest category downstream.
Wholesome water supplied by the water undertaker, the only water used to fill a drinking water installation for testing.
Wholesome water supplied by a water undertaker, complying with the drinking water regulations. It is the only water used for filling, testing and flushing a potable system.
Category 1 water whose aesthetic quality has been impaired by a change in temperature, or by substances or organisms altering its taste, smell or appearance, but which is not a health risk. Hot water, cold water that has warmed up, and hot and cold meeting in a mixer are category 2. Schedule 1 sets no temperature figure: any change is enough.
A backflow risk from water that is a slight health hazard, such as bath water, protected against by a double check valve.
A significant health hazard from toxic substances: chemicals, carcinogens, pesticides and environmental organisms of health significance. Heating primaries outside a house, sprinklers with antifreeze, porous garden hoses, commercial dishwashers and car wash plant are category 4; the highest category any mechanical device can protect against.
A serious health hazard from pathogens, radioactive or very toxic substances, including faecal and other human or animal waste. WC pans, urinals, bidets, kitchen sinks in any premises, hospital basins, animal troughs, non-domestic hose union taps, rainwater and greywater are category 5, and only an air gap protects against it.
Passing clean water through a new or altered installation at a good velocity to clear out flux, swarf, debris and stagnant water before it is used. Schedule 2 paragraph 13 requires it before first use and BS EN 806-4 sets the method; it comes before disinfection, and a booster installation is flushed again after maintenance.
The vessel that stores and delivers the flush volume for a WC or urinal. Every one except a pressure flushing cistern carries an indelible internal line showing the flush volume.
The speed of the water during a flush: at least 2 m/s for a plain water flush, or 0.5 m/s for a pulsed water/air flush.
The paste applied to copper pipe before soldering to clean the metal and let the solder flow. Most fluxes are acidic and corrosive, so excess flux left inside new pipework is the commonest cause of internal corrosion; use the least that will make the joint and flush it out before use.
A unit fitted under a sink that grinds food waste into a paste and flushes it into the drainage system through a 40 mm outlet.
The bottom of a discharge stack, where it turns into the drain. Positive pressure is greatest here, so low branches are kept clear of it.
A recorded inspection of access equipment carried out at set intervals, for ladders every three months, in addition to pre-use checks.
The contaminated air inside a drainage system. A trap seal, an intact pipe and a correctly seating valve are what keep it out of the building.
Waste water from a sanitary convenience or bidet, from an appliance used for washing foul receptacles, or water used for food preparation, cooking or washing.
A buffer with separate generator and emitter connections, giving hydraulic separation between the two circuits at the cost of mixing, which lowers the temperature reaching the emitters.
A buffer vessel with separate connections for the heat source and the system, adding both volume and separation, at the cost of mixing that lowers the system side temperature.
The chlorine in the dosed water that is still available to disinfect, measured in mg/l; dosed at 50 mg/l and read as a residual at the end of the contact time.
The chlorine still available in the water at the end of the contact period, measured in mg/l. It shows how much chlorine the system consumed and whether the disinfection worked.
The depth of gutter left above the design water level. A gutter test fills to the overflow level or to the lower level of the freeboard.
A cold burn caused when a liquid such as refrigerant boils on contact with skin and rapidly draws heat out of the tissue.
A multiplier in BS EN 12056-2 that allows for how often the appliances are used, from 0.5 for a dwelling up to 1.2 for special use.
The pressure lost as water flows through pipework, fittings and valves, which the pump must overcome on top of the static lift.
The lifting of ground and pipework caused by soil freezing and expanding. In a ground array it is a symptom of an undersized collector.
Measures such as insulation or draining that stop a system standing full over winter from freezing.
A protection control that fires the boiler when air temperature approaches freezing, always used with a pipe thermostat, and overriding all other controls.
Flow that fills the whole cross-section of a pipe. In a branch discharge pipe it is what makes siphonage possible, because air cannot get past the water.
An underfloor installation serving the whole dwelling from one or more manifolds, with room-by-room control and a heat source that can run at low temperature throughout.
The number of hours a system would run at full output to deliver its annual heat. It is the run-hours assumption behind a ground collector design.
One of the two ways of notifying building control: drawings and a specification are deposited and approved before work starts, then the work is inspected. It suits larger or more complex jobs; a building notice is the alternative.
An application depositing detailed drawings and specification with the local authority so that the design can be checked before work begins.
A solar primary circuit that stays full of fluid at all times, in contrast to a drain-back system. Every component in it must be rated for the collector's stagnation temperature.
A system in which both the heating circuit and the hot water primary circulate by pump, so both can be controlled electrically. Required by the current standards.
A control that makes the system work correctly day to day and protects the water supply, such as the strainer, reducing valve, check valve, expansion device and control thermostat. The expansion relief valve is listed with them too, although its job is safety.
A test that proves a piece of equipment is properly mounted, adjusted and installed and operates correctly, by running it through its intended operation.
Running the system through its cycle to prove that the switchgear and controls operate correctly.
A fixed accessory by which appliances are connected to the fixed wiring, containing a replaceable cartridge fuse link. Made to BS 1363-4 and available switched or unswitched, with or without a flex outlet.
A fused connection unit supplied as a spur from an existing circuit rather than by its own circuit from the consumer unit. The usual way of feeding heating controls.
A parallel pipe thread size, the half inch thread used on the tails of most basin and sink taps; G three-quarters is the three-quarter inch thread of a bath tap. The AUK2 tap gap is set by this thread size: 20 mm up to G half, 25 mm up to G three-quarters, 70 mm above G three-quarters.
Corrosion that occurs when two dissimilar metals are joined in water, which acts as an electrolyte: the less noble metal corrodes away. Galvanised steel downstream of copper is the worst case because dissolved copper plates on to the zinc and sets up cells throughout the steel; an insulating connector breaks the electrical path but does nothing about copper already in solution.
A chart with activities listed down the side and time across the top, each activity shown as a bar spanning the period it occupies. Another name for a work programme.
The statutory regulations covering work on gas appliances and pipework in Great Britain. Positioning a boiler to the manufacturer's instructions is part of complying with them.
A full-bore isolating valve with a sliding gate, fitted first on the pump delivery pipe so the system can be shut off for work.
The town and country planning order that grants permitted development rights and sets their conditions. It is amended from time to time.
A standard assessment covering a type of work a company does regularly, which must still be checked and adapted for the particular job and place.
A colourless, odourless antifreeze mixed with the water in an indirect solar primary circuit to stop it freezing. The proportion is set by the manufacturer.
The fall of a pipe, given in millimetres per metre of run. 18 mm per metre is about 1 in 55.
Water circulating without a pump because hot water rises and cooler water falls. It can move heat upwards only.
Circulating the cleaner with the help of the system pump, then repeatedly draining and refilling the whole system with fresh water until the water runs clear.
A private supply where the source is higher than the house and water flows in from a catchment tank without a pump.
A chamber that separates grease from kitchen wastewater. Appliances discharging heavy concentrations of solid matter should not discharge into one.
Coloured sleeving fitted over a bare circuit protective conductor at a termination so that the core is identifiable, as required by Regulation 514.3.2.
Waste water from baths, showers and basins that is collected, treated and reused for WC flushing or irrigation. Like rainwater it is non-wholesome, so BS 8525-2 requires identified, separate pipework and notification to the water supplier before work starts where there is a mains supply.
Electricity drawn from the public network, as opposed to generated on site. On today's factors (SAP 10.2) it carries less carbon per kWh than natural gas, though it is still the dearer fuel per kWh.
A rubber or plastic bush fitted in a hole or knockout so a cable passing through it is not cut or abraded by the edge.
The complete buried collector serving a ground source heat pump, made up of one or more circuits of pipe.
The buried pipework that takes heat from the ground for a ground source heat pump. Forms include the coiled slinky in a trench, straight horizontal loops and vertical boreholes.
The buried or submerged pipework through which brine collects heat from the ground or from water. Also called the ground loop or ground collector.
A heat pump that collects low-grade heat from the ground through a buried collector and raises it to a useful temperature for heating and hot water.
An arrangement where several similar appliances are served from one thermostatic mixing valve. It is not recommended where the occupants are high risk.
HSE guidance on electrical test equipment for use by electricians. It covers probes, leads and the safe proving of test instruments.
A test instrument for proving the presence or absence of voltage, built to the HSE guidance note GS38 so that exposed metal at the probes is limited.
A recommended water quality figure given in BS 8525-1 for treated greywater. There are no statutory water quality limits for non-potable re-use, so these guideline values are what a well-run system is judged against.
A trapped fitting at ground or basement level that receives waste water discharges before they enter the drain.
A bronze alloy of copper, tin and zinc that resists dezincification and corrosion, so it is the traditional material for valves and fittings that will be buried, concealed or used on aggressive water. Schedule 2 paragraph 7 requires concealed fittings and mechanical backflow devices to be gunmetal or dezincification-resistant.
The opening in the gutter that connects it to the rainwater pipe. It is often the part that limits the capacity of the whole system.
A room used for sleeping or living. MCS 020 a) excludes bath and toilet facilities, service rooms, corridors, laundry rooms, hallways and utility rooms, and heat pump noise is assessed 1 m from any door or window of one in a neighbouring property.
The semi-circular gutter profile used on most domestic properties. The Approved Document H sizing table is based on nominal half round eaves gutters laid level.
The small bellows or bulb pump used to raise the air pressure inside sanitary pipework to the test figure.
The point at which the completed installation is passed to the client, with the tests done, the certificates and instructions given, and the system demonstrated. Tests such as the dye test must be completed and recorded before it.
The documents left with the customer at completion: certificates and schedules, the commissioning record, manufacturer's instructions and a system schematic.
The injury or ill health that a hazard could cause, such as a fall, a burn, a laceration or a lung disease.
Anything that has the potential to cause harm, such as a chemical, electricity, a naked flame, a wet floor or an unsupported excavation.
Pressure expressed as the height of a column of water: 1 m head is about 9.81 kPa, so 10 m head is roughly 1 bar (100 kPa). Pipe sizing works in head because the pressure available from a cistern is simply the vertical height from its base to the outlet.
The vertical distance a body of water falls in a hydro scheme. With flow rate it is one of the two criteria that decide whether micro hydro is viable.
The pressure lost to friction as water flows along a pipe, expressed as metres of head and usually read from a pipe chart as head loss per metre of pipe for a given flow and diameter. The total for a section is head loss per metre multiplied by the effective length.
The manifold along the top of an evacuated tube collector, carrying the heat transfer fluid past the condenser of each tube.
The principal piece of health and safety legislation in the UK. It sets out the general duties of employers, employees and the self-employed, and the more detailed regulations sit under it.
The government body responsible for the regulation and enforcement of workplace health, safety and welfare law in Great Britain.
The file handed over on a construction project holding installers' details, method statements and permits; on a large contract the handover documents form part of it.
The person accountable to senior management for health and safety on site, including safety inspections, records, accident investigations, training and inductions.
The employer's written statement of its health and safety intentions and the arrangements for carrying them out. It must be written down where five or more people are employed.
A profiled aluminium plate that holds the underfloor pipe and conducts the heat sideways across the floor. Also called a heat transfer or spreader plate.
Any component that gives up the heat carried by the system water to the room, such as a radiator, a convector, a skirting heater or a heated floor.
Heat entering a space from a source other than the heating system, such as sunlight, people, electrical equipment or a warmer adjoining room.
The standards term for the appliance that produces the heat, normally the boiler. BS EN 12828 uses it so the same rules cover boilers, heat pumps and heat exchangers.
The rate at which heat is delivered into the stored water, in kilowatts. For an immersion or a direct-fired heater it is the appliance output; for an indirect cylinder it is an average value across the reheat.
A radiator left permanently open on a solid fuel system so that heat can escape when the pump stops or the controls close. It is connected top, bottom, opposite ends so it circulates by gravity.
A figure from the collector test data describing how quickly efficiency falls as the absorber becomes hotter than the surrounding air. First and second order coefficients are quoted.
A sealed pipe inside an evacuated tube containing a volatile liquid that vaporises, rises, condenses at a heat exchanger in the header, and drains back.
A hot water storage vessel designed for a low temperature heat source, with a much larger coil, typically about 3 square metres, so that it can absorb the available power across a small temperature difference.
The time taken for the heat source to bring a full cylinder of cold water up to its set temperature after the hot water has been drawn off. Also called the recovery time.
A shaped aluminium plate that holds the pipe and spreads its heat across the underside of a timber floor.
The fluid circulated between collector and store, usually water with glycol antifreeze and a corrosion inhibitor package. Its condition and pH are service checks, not fit-and-forget items.
Flexible cable with insulation rated for higher temperatures than ordinary PVC, used where the cable must run close to a heat source such as a boiler or primary pipework.
A pipework run serving a number of radiators that is controlled by its own zone valve. Two thermostats on one valve do not make two circuits.
The pipework carrying water between a boiler and the radiators or a cylinder coil; the primaries. In a house it is fluid category 3, and outside a house category 4, which decides the backflow device on any connection to the supply.
The extra output allowed so a building can be brought back to temperature after the heating has been off, rather than only held at temperature once warm.
The order in which controls are chosen: eliminate, substitute, engineering controls, administrative controls, and personal protective equipment last.
A fuse able to interrupt a very large fault current safely. Fitted in test leads so a wrongly set instrument cannot release the full fault energy.
A second, independent temperature control, also called an energy cut-out, that removes the energy supply if the working thermostat fails. It is either manually reset or non-resettable.
The pressure switch set at the cut-out pressure that stops the pumps once the required system pressure is reached.
The overheat protection that shuts the heat source down if the water temperature rises too far, for example when circulation stops.
The column in BS EN 806-3 Table 3 giving the largest single draw-off, in loading units, that a pipe size may feed however small its total load. It stops a 4 LU bath being fed through a size rated for a 2 LU appliance.
The time for which the test pressure must remain constant. For sanitary pipework it is at least 3 minutes.
Ground loop pipework laid in trenches a few metres below the surface. It is the cheapest collector to install where land allows, but needs a large area of ground.
A centrifugal pump with one impeller on a horizontal shaft, for modest heads.
A small check valve screwed onto an outside tap to stop water siphoning back up a hose. It is tested by filling the hose from the tap, closing the tap and checking that the hose drains, and is replaced if it fails.
A tap with a threaded outlet that a hose can be screwed onto, usually a bib tap outside a building. Because the hose end can lie in contaminated water it is a backflow risk: fluid category 3 in a house garden, protected by a double check valve inside the building, and category 5 in non-domestic premises.
Running the system to maximum operating temperature and then draining it while hot, so that oils, flux residues and jointing compound are carried out with the water.
The heat input needed to reheat a stored hot water cylinder from the incoming cold temperature to the storage temperature within a chosen recovery time.
A control arrangement in which a call from the cylinder closes the heating zones so that all the available output goes to reheating the stored water.
Item 2 of the Regulation 5 table makes extensions and alterations of a water system notifiable only in premises other than a house. The exception covers only item 2: the item 4 fittings, such as a large bath, a pump over 12 litres a minute or an RPZ valve, are notifiable in a house as anywhere else.
A house shared by more than one household. It is not a single-family dwelling, so the disinfection exception does not apply.
The Health and Safety Executive's Approved Code of Practice on the control of Legionella bacteria in water systems. It sets out the duty to assess and manage the risk in stored and warm water.
The Health and Safety Executive’s code on the control of Legionella bacteria in water systems. It sets the duty holder’s responsibilities in non-domestic buildings for risk assessment, monitoring and record keeping, and identifies 20 °C to 45 °C as the growth range.
A heat pump and a boiler under a single intelligent controller, which selects whichever source is cheaper or more efficient at the current conditions.
A pressure vessel with an air or nitrogen pre-charge that stores pumped water under pressure. It usually has one pipework connection and needs a check valve on its supply side.
The flow in litres per second that a given size of pipe or stack can carry. The chosen pipe must have a hydraulic capacity at least equal to the calculated flow rate.
A mechanical valve on a urinal supply that opens on a drop in hydrostatic pressure when other fittings are used, passing a measured amount of water to the cistern.
A pressure surge, also called water hammer, set up when moving water is stopped suddenly, for example by a check valve slamming shut. It can damage fittings and cause noise.
A urinal flushing control that admits water to the cistern only when water is drawn from a nearby fitting, so flushing follows use.
The power a pump puts into the water, in watts: flow in litres per second × 9.81 × head in metres. Dividing by the pump efficiency gives the motor power needed; 0.2 l/s at 17 m is 33 W, about 56 W at 60 per cent efficiency.
A leak test carried out with water raised by a test pump to a set pressure and held for a stated time. Underfloor circuits are tested before the screed goes down.
An arrangement in which two circuits exchange heat through a common vessel but not flow, so the pump on one side does not affect the flow rate on the other.
A soundness test carried out with water rather than air, taking the system to one and a half times the maximum working pressure and checking for pressure loss and visible leakage.
The hand or powered pump used to raise a water-filled system to test pressure, with a calibrated gauge accurate to 0.2 bar at the lowest point.
A gutter whose length is not more than 50 times its design water depth. Longer gutters have their design capacity reduced by a capacity factor.
A pressure test carried out with water rather than air. Water is used because a failure releases very little stored energy, unlike compressed air.
What the end user can tell you about a fault: when it first occurred, how it was noticed, whether it is constant or intermittent, any noises, any attempted repairs and what the result was. It is gathered by verbal discussion, not by measurement.
An electric heating element fitted into a hot water storage vessel. Used as a main heat source, as summer or backup heating, or to run a pasteurisation cycle.
The rotating vaned wheel inside a centrifugal pump that throws the water outwards and creates the pressure. If the shaft driving it breaks, the motor runs but no water moves and the outlets run dry.
Load that comes and goes, such as snow on a roof, people, or stored water. It is assessed alongside dead and wind loads.
A written record of what was wrong, what standard is required, what support is offered, and when performance will be reviewed.
In its actual place; a measurement taken in situ is taken in the building itself rather than off a drawing. Needed where there are no drawings, or where the drawing and the building disagree.
A mixing valve fitted in the pipework rather than at the tap, used to hold the hot water supplied to an appliance such as a bath below its maximum temperature.
A device fitted permanently in the system water circuit, commonly using a magnet, that captures and allows the removal of circulating solid particles.
A removable mesh filter fitted on the cold supply to an unvented cylinder to catch debris before it reaches the control valves. It has to be accessible for cleaning.
Inspection and checking of work while it is being carried out, recorded so there is evidence of the check once the work is covered.
A separate time channel for a circuit, so that its on and off times can be set without affecting any other circuit.
The circuit in a system with the greatest total resistance to flow, normally the longest run to the most remote emitter. The pump is sized from it.
Boosting where the pumps draw from a break cistern rather than the supply pipe, so there is no limit on pump capacity.
A hot water storage vessel containing a heat exchanger, so that primary water from the boiler heats the stored secondary water without mixing with it.
Distribution in which harvested water is pumped to a cistern at high level, which then supplies the outlets by gravity and receives the mains top-up.
A cold water system where the outlets, apart from the drinking tap, are fed from a storage cistern.
Unwanted electrical noise picked up by a signal cable from a nearby mains cable, which can make sensor readings drift or jump.
Loss of the seal from a trap that is not in use, caused by suction from another appliance discharging into the same branch or stack.
Dealing with a first or minor performance problem by private conversation, agreeing the standard and setting a review, without invoking the formal procedure.
A hands-free tap whose sensor eye opens a solenoid valve when the beam is broken by the users hands. Runs on 6 V DC.
A tap opened by breaking an infrared sensor beam, which signals a solenoid valve to pass water for as long as the beam is interrupted.
A chemical added to heating system water to slow corrosion and scale. A large system dosed with inhibitor outside a house is fluid category 4, so a permanent fill to it needs a type BA RPZ valve.
The controlled first warming of a heated screed: 20 to 25 °C for at least 3 days after the curing period, then the design temperature for at least 4 more days.
A notice given jointly by the client and an approved inspector, transferring the building control function from the local authority to that inspector.
The inspection and testing carried out on a new installation, or an addition or alteration, before it is put into service. It is set out in Part 6 of BS 7671.
A two-port valve that meters hot primary water into a recirculating manifold circuit to hold the blended temperature, as an alternative to a three-port mixer.
The set of valves fitted in order on the cold supply to an unvented cylinder: isolating valve, line strainer, pressure reducing valve, single check valve, expansion vessel connection and expansion relief valve.
The set of controls on the cold feed to an unvented cylinder: a line strainer, pressure-reducing valve, single check valve, expansion relief valve and often the expansion vessel connection, usually in one assembly. The check valve stops expanded hot water flowing back into the supply.
Corrosion-resistant mesh of 0.65 mm maximum aperture over cistern vents and overflows to keep insects out.
The solar energy accumulated on a surface over a period, measured in kilowatt hours per square metre. Also called irradiation.
The visual examination of an electrical installation, carried out before testing and normally with the supply disconnected, to verify correct selection, erection and condition.
The document describing the installation to be priced and built: the materials, the appliances, any manufacturer or British Standard they must meet, and the performance the system must deliver such as flow rates and pressures at outlets. Read with the manufacturers' data it defines what the design calculation has to achieve.
A heater with no storage that heats water as it flows through. It delivers hot water for as long as the tap runs, but only while water is flowing.
The periodic checking of a test instrument against a known reference so its readings can be relied upon, and recorded so results can be defended.
The resistance measured between conductors, or between conductors and earth, at a raised DC test voltage. It shows whether the insulation has broken down. Minimum 1 megohm at 500 V DC on a 230 V circuit.
An electrical test that confirms there are no low resistance paths between circuit conductors, or between conductors and earth.
A trap built into an inspection chamber on a drain to stop sewer gases and vermin passing towards the building. A drain with one needs an open ventilating pipe, not an AAV.
A payment made to a contractor during a contract, based on the work measured and valued up to that date.
A pressure test on a section of work as it proceeds, especially work that will be concealed or buried; it does not replace the final test.
Two or more cisterns of the same size piped together to provide the total storage, arranged so water flows through all of them.
A fault that comes and goes rather than being present all the time, for example a noise heard only while a WC cistern refills. It is harder to find because it may not be there when you arrive, so the user's account of when it happens matters.
An addition of about fifteen per cent to a calculated heat loss to allow for the system running only at set times, so rooms can be brought back up to temperature quickly.
A department or section within the same company or organisation that raises work for the in-house team to carry out.
The temperature a room must reach when the heating system is running. It is chosen from the room's use and agreed with the customer.
An arrangement in which the expansion is taken by an air pocket at the top of the cylinder, held above a floating baffle plate. Known as a bubble top cylinder.
An air gap held at the top of some unvented cylinders that takes up expansion instead of an external vessel. The air slowly dissolves into the water and the gap must be recharged by draining down and refilling.
An arrangement that discharges excess water from a cistern into the pan rather than through an external warning pipe. It is accepted only where a strainer is fitted at or upstream of the float-operated valve.
A collar fitted round a plastic pipe where it passes through a fire separating element. In a fire the intumescent material expands and crushes the softening pipe closed, sealing the opening.
The lowest point of the inside of a pipe; the level from which warning pipe and overflow heights are measured.
A compressor whose speed can be varied to match the heat demand, instead of running at full output or stopping.
The document issued at the end of a contract demanding final payment for the work carried out.
The rate at which solar radiation falls on a surface, measured in watts per square metre. It is an instantaneous power, not a total.
A valve fitted so that a component can be shut off and worked on without draining the system. Pumps have one on each side.
Shutting off the water — and on a boosted system the electricity — to the part of the system being worked on, making sure it stays off, and telling people why. The sequence is isolate, label, leave contact details, cap off.
The switch that disconnects the electrical supply to a pump set or control panel. It is switched off, proved dead, locked off and labelled before any mechanical work starts.
A three-dimensional drawing of pipework in which the three axes are drawn at 30° to the horizontal so vertical and horizontal runs can both be shown. The isometric used for pipe sizing is best drawn to scale, with each junction numbered, as the withdrawn BS 6700 (Annex D) recommended.
A three-dimensional projection of the pipework used for setting out; a projection, not a record of what was installed.
The record of a single visit, listing the work carried out, parts used and time taken.
A written description of the installation being priced, giving the types, models and quality of materials and appliances, and often the British Standard to be met.
A paste applied to screwed pipe threads to make them watertight; for drinking water it must be to BS 6956 Part 5 so it does not taint the water. PTFE tape, the thin plastic tape wound round a thread for the same purpose, is made to BS 6974.
The disc inside a screw-down tap that carries the washer and sits on the seat. If it is loose it chatters in the flow, so the tap vibrates and gives a poor flow.
An enclosure containing terminals for joining cables. In heating work it is used for control wiring on a circuit that already has adequate fuse protection, not to supply equipment straight from a main circuit.
Materials delivered to the exact location of the work at an agreed time that coincides with the operatives starting that work, so nothing is stored on site longer than necessary.
A method of supply in which materials arrive at the exact location of the work at a time that coincides with the operatives beginning that work.
The unit used in the standards for a temperature difference; a difference of 10 K is the same as 10 degrees Celsius.
Banging or rumbling boiler noise caused by scale or sludge on the heat exchanger, which makes water boil locally against the fouled surface.
A unit of energy: one kilowatt delivered for one hour. Dividing kilojoules by 3600 converts them to kilowatt hours.
A gun that drives compressed air against a column of water to send a shock wave at a blockage. Used only on compacted soft material, and never where air admittance valves are permanently fixed.
A sharp, short-radius bend with no sweep. It restricts flow and, at the head of a stack, leaves an air admittance valve sitting off vertical.
Kilopascal, the SI unit of pressure used in BS EN 806. 100 kPa is 1 bar and is roughly the pressure of 10 m of water; 500 kPa is 5 bar.
The number of people, and the hours they work, allocated to an activity. A bar chart carries a space to record it.
The people available to do the work, expressed as the number of operatives and the periods for which they are needed.
A cut or tear of the skin, the typical injury from handling thin sheet metal casings, cut pipe ends and broken cast iron.
Insulation wrapped round pipework and cisterns to stop heat loss, frost damage and cold water warming up, and to stop pipes vibrating against the structure. Pipes under floorboards that are not lagged are a common source of noise.
The place a person steps off a ladder onto a platform, floor or loft. The ladder must extend at least a metre above it to give a handhold.
A hand-held instrument that measures a distance by bouncing a laser off a surface, accurate to about 3 mm, used by one person and unaffected by sag or obstacles. The most accurate site measuring instrument.
Heat involved in a change of state, such as the evaporation of moisture from skin and breath, without a change in temperature. A person at rest gives off about 50 watts of it.
A certificate from the local planning authority confirming in writing that proposed work is lawful without planning permission.
A drawing that shows components in their true physical positions on the plan of the building. Used to find where appliances and vessels are to go.
The time between placing an order and the goods being available. A long lead time on a specified item is a common cause of programme pressure.
Solder for joining copper pipe on water services that contains no lead, made to BS EN 29453. Lead solder is banned on drinking water pipework because lead dissolves into the water; lead-free solder is tin with a little copper or silver.
A soap-based solution brushed onto a joint or valve so that escaping gas or air forms visible bubbles. Used to confirm whether a Schrader valve is leaking.
An automatic shut-off valve that closes on detecting a leak, functionally tested like any other control.
The bacteria that cause Legionnaires' disease, a serious pneumonia caught by breathing in fine water droplets. They multiply in stagnant water between about 20°C and 45°C, which is why cold water is kept below 20°C, storage is kept small and dead legs are avoided.
The bacterium that causes Legionnaires' disease. It is contracted by inhaling an aerosol of contaminated water and multiplies between 20 and 45 degrees C.
The maximum fine for an offence under the Water Fittings Regulations, set by Regulation 7. The standard scale is the set of fine levels used by magistrates' courts; level 3 is currently 1,000 pounds.
An arrangement with no step or threshold to cross, which is why a wet room suits users with limited mobility.
A level-sensing device with an audible or visual alarm that may replace the warning pipe on cisterns over 5,000 litres.
Running a private supply pump from a float switch in the roof cistern, so every outlet is cistern fed at low pressure.
A tap with a long lever that can be worked with the wrist or elbow, chosen where hands must not touch the tap.
Legal responsibility for a cost or a loss. Where a variation results from defective workmanship, liability for the extra cost can fall on the contractor.
The temperature gap a heat pump must bridge, from its source temperature up to the flow temperature it delivers. Widening the lift reduces efficiency.
Replacing a component with one of the same specification. Where that is not possible, the manufacturer confirms the alternative is approved.
Replacing a failed part with the same make and model, or with the manufacturer’s own spare, so that the component performs exactly as designed and its approvals and warranty are unaffected.
Replacing a failed component with one of the same type, rating and capacity, or with a part the manufacturer has confirmed is approved for use with that appliance.
The judged chance of an accident occurring, scored on a scale running from no likelihood through unlikely and likely to certainty.
Calcium carbonate deposited from hard water in the hottest part of the system, usually the boiler heat exchanger, where it reduces heat transfer.
The height up a building that the water main can serve on its own. Floors above it need pumping.
The maximum heat a floor heating system may give per square metre, fixed by the maximum permitted surface temperature. 100 W/m² in occupied areas and 175 W/m² in peripheral areas.
The worst U-value a new element may have and still comply, sometimes called the backstop. It is a floor, not a target: the value actually built to is normally better.
The boundary of what a person at a given level of qualification and responsibility may decide or do without referring it upwards.
A simple diagram, not drawn to scale, showing appliances, pipe runs and their sizes as single lines. It is the industry convention for presenting a sanitary pipework design to a customer.
A mesh filter fitted in the pipe immediately upstream of a category 4 backflow device such as an RPZ valve to keep grit out of its check valves. A gradual loss of flow downstream usually means the strainer is blocked.
A long narrow floor gully, often set against a wall, that collects shower water across its length instead of at a single point.
A building on the statutory list because of its special architectural or historic interest. Work to it needs consent, and permitted development rights do not apply.
A document that is kept current and available where the work is happening, updated as the job changes rather than filed once and forgotten.
A test that requires the circuit to be energised, such as earth fault loop impedance, prospective fault current and RCD operation. Only competent, skilled persons carry these out.
The object being handled. In the regulations a load may be inanimate, such as a box or a boiler, or animate, such as a person or an animal.
A control function that varies the flow temperature from the heat generator according to the measured response of the heating system.
A number given to each type of outlet that allows for its flow rate, how long it runs and how often it is used, so that the outlets on a pipe can be added up and converted to a design flow. In BS EN 806-3 one loading unit equals 0.1 l/s: basin and WC 1, sink and shower 2, bath 4, garden tap 5.
The district, borough or unitary council. In water work it enforces the Private Water Supplies Regulations, inspecting and testing private supplies, and enforces the Building Regulations through its building control department; it does not enforce the Water Fittings Regulations, which is the undertaker's job.
A switch or fused connection unit at or beside the equipment, allowing it to be switched off for servicing without disturbing other circuits in the building.
A system in which a small heater is fitted at the outlet it serves. Also called a single point or point of use system.
A small repair or an inserted junction in an existing pipe. The fitting is immersed in disinfectant before fitting rather than the whole system being disinfected (BS EN 806-4 clause 6.3.5).
Securing an electrical isolator in the off position with a lock, after proving the circuit dead, so it cannot be switched on while work goes on.
A proprietary fitting that holds a circuit breaker or switch in the off position so a padlock can be applied and the supply cannot be restored by anyone else.
A hose union tap on a non-wholesome supply fitted with a head that locks or can be removed, so it cannot be used by mistake. It is preferred to a label because it does not depend on anyone reading it.
A protective shutdown by an appliance, which then stays off until it is reset. The code shown says which protection operated.
A regulating valve with a shielded head so its setting cannot be altered by hand, used to balance the branches of a circulating system during commissioning.
The book kept on site, usually in the plant room, in which every inspection, test, maintenance visit and repair on the installation is recorded. BS 8558 expects one for a boosted installation, and PD 855468 calls the version used for Legionella control the water management logbook.
One continuous circuit of underfloor pipe serving an area, connected to the flow and return manifolds.
A large-bore vessel connected across the boiler circuit and the heating circuits, giving hydraulic separation so each side can run at its own flow rate.
The pressure switch set at the cut-in pressure that starts the pumps as water is drawn and the pressure falls.
An instrument for measuring very small electrical resistances accurately, used across disconnected motor leads to test the winding resistance. It is only used after safe isolation.
A radiator with a casing over the heating element that keeps the touchable surface much cooler than the water inside, for locations used by children, the elderly or the infirm.
A radiator with a casing designed to stay cool enough not to burn on contact. It is used in nurseries, schools, care settings and anywhere vulnerable people may touch it.
A break cistern, inside or outside the house, that collects water from a source below the house or an unreliable one, from which a surface pump lifts it.
A switch in the break cistern that stops the pumps when the water is low, preventing dry running.
An electrode in a borehole or cistern that senses when the water has dropped too low and stops the pump, doing the job of a float switch where a float will not fit.
Taps designed for cistern-fed supplies with a full-bore waterway, fitted in place of high-pressure taps to cure poor flow on a gravity system.
An instrument that can measure very small resistances accurately, used for continuity and polarity testing. Its leads are nulled before use.
A pumped unit fitted behind a WC that shreds solids with rotating blades and pumps the liquid mixture through small bore pipework to a stack or drain.
A float switch in which repelling magnets snap a micro-switch over as the float passes the set level, so the contacts change cleanly.
Black iron oxide sludge formed by corrosion in a heating system. It settles in low flow areas, blocks heat exchangers and seizes pumps.
The contractor holding the contract with the client for the building work as a whole. It appoints and co-ordinates the subcontractors.
The drain run serving a building or a group of buildings before it reaches the sewer. Approved Document H requires a ventilating pipe at or near its head.
The terminal or bar in an installation to which the earthing conductor, the circuit protective conductors and the main bonding conductors are all connected.
A conductor connecting the main earthing terminal to incoming metallic services such as water and gas, so that all touchable metalwork sits at a similar potential.
The wholesome water top-up that keeps a rainwater or greywater system working in dry weather. It enters the storage cistern or make-up module through a type AA or AB air gap above the water, never by a pipe-to-pipe connection, so only the water meets and the pipes never join.
The percentage added to a pipe section's heat duty to cover the heat the pipe itself gives up on the way, typically 5 to 10 per cent depending on the length of run.
Circulating the cleaner, then flushing the system and each radiator in turn with mains pressure water until it runs clear, using a backflow prevention device at the mains connection.
A cold water system in which every outlet is fed direct from the supply pipe at mains pressure, with no storage cistern. Also called a direct system. A combined system puts the kitchen sink on the supply pipe and the rest on a cistern, so the cistern buffers peak demand.
Keeping water fittings in working order so they do not become damaged, worn or faulty. Under Regulation 3 it is the user's responsibility, and failing to maintain a fitting that then causes waste or contamination is a contravention by the user.
The running record of maintenance work on a plant. BS EN 12056-4 clause 8.2 says a log should be kept of all maintenance work, detailing what was carried out.
The record on which maintenance and repair work is entered as it is completed, giving location, date and tests performed.
Substantial new pipework added to an existing system, treated as a new system for disinfection (PD 855468 clause 9).
Repairing the defects that testing has revealed, and restoring anything opened up to reach them, before the results are finally recorded.
The section of a method statement stating how supervisors and managers will make sure the working methods are actually followed, including regular team meetings.
Regulations requiring employers to make a suitable and sufficient assessment of the risks from their work activities, and to give particular attention to young persons before employing them.
A firm appointed to manage a property on the owner's behalf. It instructs work, agrees prices and arranges access as the owner's representative.
The common pipe header that several pumps share on their suction side and again on their discharge side, with an isolating valve and a non-return valve for each pump.
A quarter-turn valve at the end of each manifold bar allowing the manifold to be isolated for maintenance without draining the system.
A U-shaped tube part filled with water, used to read very small pressures. The difference between the two water levels is the pressure in millimetres water gauge.
Regulations covering lifting, lowering, pushing, pulling and carrying. They require hazardous handling to be avoided, then assessed, then reduced so far as is reasonably practicable.
The installation, commissioning and maintenance instructions for a specific appliance. Where they demand more than a standard, they govern, unless statute requires otherwise.
The technical document supplied with an appliance. It carries the required supply conditions, pipe sizes, heat input, controls, discharge sizing and fault-finding data for that specific model.
The document supplied with an appliance setting out how it must be installed, supplied, commissioned and maintained. It is followed where it is more demanding than a general standard.
The installation, commissioning and maintenance document supplied with an appliance. It gives the setting-up procedure and the performance figures for that model.
The literature the manufacturer supplies with a component — installation, operating, commissioning and maintenance instructions, fault-finding charts and parts lists. It is the first document to consult when diagnosing a fault on a component, and BS EN 806-5 requires it to be kept and followed.
The data sheets and installation instructions supplied with an appliance or component, giving its minimum flow rate, working pressure, connections and commissioning procedure. They give the figures for the item actually being fitted, and ignoring them voids the warranty and can put the installer in breach of the Regulations.
The installation, set-up and commissioning instructions supplied with each component. They must be followed; ignoring them can void the warranty.
The percentage added to the cost of a job to produce the selling price, covering overheads and profit.
The mass of water moving past a point each second, in kg/s. On a secondary return it is found from the heat the loop loses: kW divided by the specific heat capacity of water (4.19 kJ/kg·K) times the temperature drop.
A change to a building or to a controlled service or fitting that affects compliance with the Building Regulations. Material alterations to drains and sewers are covered by the Regulations.
A change in the purpose for which, or the circumstances in which, premises are used, so that they become a dwelling, an institution, a public building, or somewhere storing substances that would form fluid category 4 or 5. It ends the exemption for fittings installed before 1 July 1999 and is itself notifiable to the water undertaker.
The process of measuring and counting the materials required for a job directly from the drawing, listed by type and size.
The greatest current an installation or circuit is expected to draw at one time. It is assessed under BS 7671 Section 311 and is the basis for deciding whether an installation can take extra equipment.
The highest pressure an appliance or fitting is made to work at; a PRV is needed where the supply can exceed it.
The largest reduction in trap seal depth measured across the repeats of a test. It is compared against the 25 mm criterion.
The highest pressure the installation is designed to be subjected to in operation, normally the mains pressure after any pressure reducing valve. The test pressure is 1.5 times this.
The length limit in BS EN 806-3 Table 3 for the smaller pipe sizes: 15 mm copper carries 4 LU only up to 9 m and 6 LU only up to 7 m. Beyond the limit the section goes up a size.
The longest time a greywater system may hold treated water, declared by the manufacturer. When it is exceeded the water must be discharged and replaced.
The highest pressure the installation is designed to be subjected to in normal operation, usually the incoming mains pressure after any pressure reducing valve.
The Microgeneration Certification Scheme planning standard used to assess noise from an air source heat pump at a neighbouring property.
Half the sum of the flow and return temperatures of an emitter. Subtracting the room temperature from it gives the excess temperature that sets the emitter's output.
The device that safely disconnects the appliance and its controls from the supply for both electrical and mechanical safety. Its presence and operation are confirmed at commissioning.
A wheel on a handle that counts its turns as it is pushed along the ground to read a distance. Used for long external runs; more accurate than pacing, a folding rule or scaling off a plan.
Equipment used to take the weight out of a handling operation, such as a sack truck, skates, a trolley, a tail lift or a lifting device.
A backflow device with moving parts, such as a check valve, RPZ valve or disconnector, that puts a physical barrier in the pipe where an air gap cannot be arranged. Mechanical devices wear, need access and testing, and none of them reaches fluid category 5.
The float valves, servicing and stop valves, pressure reducing valves, backflow devices and booster controls that are set to the specification and manufacturer's figures at commissioning.
Physical injury to a cable such as crushing, cutting, abrasion or crimping of the sheath or insulation. It is one of the things a pre-installation inspection looks for.
A strainer fitted on the filling connection of a large job so that the filling water is free of particles of 150 micrometres or larger.
Securing the water supply and the flow into a component or section of pipework, so nothing can discharge into it while work or testing goes on.
The path taken by water shed during defrost, from the base of the outdoor unit to a drain or soakaway. If it blocks, the water refreezes at the unit.
The section of a method statement giving the site-specific sequence of work and the actual methods used to keep work areas safe and tidy at each stage.
A written description of how a job will be done safely, held with the risk assessment and any permit to work.
Milligrams per litre, the concentration unit for chlorine; one mg/l is one part per million.
Small diameter heating pipework, typically 8 mm or 10 mm, run from a manifold to individual emitters. It may be sized to a velocity of up to 1.5 m/s.
A heating appliance containing an engine or fuel cell that generates electricity while it produces heat for the dwelling.
A small-scale system generating heat or power from a renewable source for a single building, such as solar thermal or a heat pump.
A small-scale renewable energy system sized for a single building. It either produces heat, produces electricity, or produces both.
A small snap-action electrical switch operated by a float, flow paddle or lever, used inside float switches and flow switches.
A small wind turbine, pole mounted or building mounted, that generates electricity. Siting depends on average wind speed, turbulence, height, and noise and vibration.
Bacteria and other micro-organisms in water, the main risk from shallow streams and springs, dealt with by disinfection.
A two-pipe heating system whose circulation pipework is normally 6 mm to 12 mm outside diameter, fed from a pair of manifolds. Radiator legs are usually 8 mm or 10 mm.
A certification scheme for small-scale renewable technologies and their installers. It is voluntary in law but is normally required for grant funding.
The position of a three-port mid-position valve in which both outlet ports are partly open, so heating and hot water are served together.
A three-port valve that can direct flow to the heating, to the cylinder, or share it between both at once. Used in the Y-plan arrangement.
A small vessel fitted on the closed side of a check valve, between the valve and the heater, to take up the expansion of water that warms in the closed section.
The flow an outlet must still receive when other outlets are in use at the same time, lower than its design flow rate. BS EN 806-3 gives 0.15 l/s for a sink and 0.3 l/s for a bath, for example.
The least volume of water that must remain in circulation for a heat generator to run without cycling too frequently. It is stated by the appliance manufacturer.
The BS 7671 model form issued for an addition or alteration to an existing circuit that does not extend to a new circuit or a consumer unit change. One is issued for each circuit altered.
The MCS installation standard for heat pump systems, covering supply, design, installation, set to work, commissioning and handover.
One of the five harms: water used for a purpose it was not supplied for, such as a domestic supply used for an unauthorised industrial process.
A heating system serving emitters that need different flow temperatures, such as radiators at about 70 °C and an underfloor circuit at 40 to 45 °C.
A tap or shower valve fed by both hot and cold water that blends them to a single outlet. Where the waterways join before the outlet, hot (fluid category 2) can cross into the cold supply, so each feed carries a single check valve unless the fitting is bi-flow.
A heat pump with the whole refrigeration circuit in the outdoor unit, so system water is carried outdoors between the unit and the building.
An air source heat pump in which the whole refrigerant circuit is contained, sealed and factory-charged inside the outdoor unit. Only insulated flow and return water pipes enter the building.
A system in which one kind of heat source covers the whole heating demand at all times, even where two machines of that kind are used together.
The draw-off furthest from the riser on a floor, opened first during flushing so the whole branch is scoured.
A protective switch that cuts the supply if the motor draws more current than its set value. Its setting is recorded at commissioning under BS EN 12056-4 clause 7.
The coils of insulated copper wire inside a motor that produce its magnetic field. Their resistance, measured with a low resistance ohmmeter after safe isolation, shows whether a winding is shorting (a low reading) or going open (a high reading).
An electrically operated valve in the primary circuit that opens to let heat reach the cylinder coil. It is switched by the cylinder thermostat and closed by the overheat thermostat.
An electrically operated valve that opens or shuts one circuit. S-plan uses one per circuit, driven by the room or cylinder thermostat.
For cold water design, a building with more than three floors, where the mains pressure may not reach every outlet.
A system in which several areas each have their own zone valve, room thermostat and time control, so each area is heated independently.
Treating water in several stages, settling, filtering and then disinfecting, so no single stage has to remove everything.
A gas fired instantaneous heater that supplies several outlets from one appliance, heating mains water on demand with no storage.
A two-part brass ring clip screwed to a backplate or hung from tapped rod. It is used where pipes run in banks or are suspended from a ceiling.
Modified unplasticised PVC, a plastics material used for waste pipework. Like ABS and PVC-U it is damaged by the naphtha in chemical smoke.
A hydrocarbon present in chemical smoke that attacks plastics. It is the reason smoke testing is avoided on ABS, PVC-U and MUPVC pipework.
A section added to a European Standard giving the practice used in one country. National Annex NG of BS EN 12056-2 gives the UK inspection, testing and maintenance methods.
An event that did not cause injury but could easily have done so. It is investigated in the same way as an accident and triggers a review.
An installation where the cistern is below the pump or the shower head is above the cistern, so water will not flow on its own and the pump needs a pressure vessel or transducer to start it.
A shower pump designed to start and run where there is little or no head of water above it, sensing the drop in pressure rather than the flow.
A screwdriver with a neon lamp in the handle. It relies on current flowing through the user, gives no reliable indication of absence of voltage, and must never be used to prove dead.
The total volume a storage vessel holds, as marked on the label. Only part of it comes out hot enough to use.
An individual radiator control communicating with a central controller, which can be used in every room on a circuit instead of a room thermostat plus TRVs.
The position at which the cold feed and vent connect to the system, where system pressure stays the same whether the pump runs or not.
An additive used to pacify an acid-based descaling cleanser before the system water is discharged, so the effluent is not harmful to the drain or the environment.
An approved chemical added to spent chlorinated water to remove the chlorine before discharge, where the sewerage undertaker requires it.
Installation work carried out as part of the construction of a new building, programmed inside the main contractor's overall site programme.
Holding a reduced room temperature overnight or during unoccupied periods instead of switching the heating off, which limits condensation risk and speeds recovery.
The shaded area on a discharge stack opposite a branch connection, given in BS EN 12056-2, inside which no other branch centre line may be placed.
The size designation used for a pipe in the European standards. It is a reference number, close to but not always identical to the actual internal or external diameter.
A subcontractor named by the architect in the original contract, who must then be used with the client's permission.
A self-closing tap with a spring-loaded plunger that runs for a set time, up to about 20 seconds, then closes itself. Named for cushioning the closure against hammer.
Air or other gases that will not condense at circuit conditions. They raise pressures, reduce performance and usually indicate poor evacuation or a leak.
A finding at audit or inspection that something required has not been done or not been recorded.
A single-pole detector that senses a live conductor without touching it. GS38 permits its use for identifying live equipment only, never for proving dead.
Backflow protection that works by an arrangement rather than a moving device: the air gaps (types AA, AB, AD, AG, AUK1, AUK2, AUK3) and the permanently vented pipe interrupter (type DC). The Regulations and BS 8558 prefer it to mechanical devices wherever practicable.
Any water other than potable water, sometimes called unwholesome water. Harvested rainwater and treated greywater are non-potable.
A valve that lets water flow one way only, fitted on a pump delivery so the column cannot run back through the pump.
A safety device that disconnects the supply of heat if the store overheats and stays off until it is reset by hand. Also called the overheat thermostat, thermal cut-out or high limit thermostat.
A single (EB) or double (ED) check valve without a test point. Because it cannot be tested in place, BS EN 806-5 has it replaced every 10 years.
Water that does not meet drinking water standards: rainwater, greywater, recycled water or water from an untested private source. It may be used for WC flushing and irrigation, but its pipes must be clearly identified and never cross-connected with the wholesome supply.
The pressure a system runs at in service: mains pressure, cistern head or pump working pressure. The initial fill is made at this pressure, not the test pressure.
The label, or the equivalent prohibition sign from BS EN 806-2, fixed at every outlet on a non-wholesome supply in premises other than a house. On a site where most outlets are non-potable the few potable ones may be marked instead, as long as one convention is used throughout.
A cut in the top or bottom edge of a joist to let pipework pass. Approved Document A limits its depth to one eighth of the joist depth.
The written information a person proposing notifiable work must give the water undertaker before starting: their name and address, a description of the work, the location and use of the premises, and in most cases a plan of the premises and a diagram of the pipework. It is normally given on the undertaker's notification form.
The notice given to the building control body confirming that commissioning has been carried out to an approved procedure. It is due within 5 days under a building notice, or 30 days for scheme-registered work.
Work that must be notified to a building control body. Installing an unvented hot water system is notifiable, in advance unless the installer is scheme-registered.
Work that must be notified to the water undertaker before it starts under Regulation 5, such as a pump drawing more than 12 litres per minute from a supply pipe.
Work that the law says must be reported to an authority before it starts: to the water undertaker under Regulation 5 of the Water Fittings Regulations for the operations in its table, and to the building control body under the Building Regulations for building work. Doing notifiable work without notice and consent is an offence.
Setting a low-resistance ohmmeter to ignore the resistance of its own test leads, so the reading is of the conductor alone.
The number of people living in a dwelling. It is the main driver of hot water demand and the basis of most storage sizing figures.
When and for how long a building is occupied, and by how many people. It affects control choices, the intermittent heating allowance and the hot water load.
The part of a heated floor where people normally stand or walk. Its surface temperature is limited to 29 °C at a room temperature of 20 °C.
A property in use by its occupants while the work is carried out, which limits working hours, access and the services that can be taken out of use.
The higher static pressure in the main at night when demand falls; a split float-valve washer lets by under it.
A change of direction in a discharge stack. In the wet part of the stack it causes suction below and positive pressure above, so it is avoided where possible.
An ornamental gutter profile with an S-shaped front face, common on Victorian buildings and often required on period terraces.
A heating layout in which a single ring of pipe leaves the boiler and returns to it, with both tails of every radiator connected to that ring. Water cools progressively round the loop.
A break in a conductor or winding, so no current can flow. An instrument shows it as infinity or OL.
A system that abstracts water from a well, borehole or watercourse, takes heat from it through a heat exchanger, and returns or discharges it. It normally needs an abstraction licence.
The open pipe from an open vented system that rises above the feed and expansion cistern and turns over it, providing a permanent path to atmosphere. It rises at least 450 mm above the water level.
The safety pipe that rises from the system and discharges over the feed and expansion cistern. It gives steam and expanding water an unrestricted path to atmosphere and may never contain a valve.
The pipe from the top of the hot water storage vessel or draw-off to a point above and over the cistern water level. It keeps the system at atmospheric pressure and acts as a safety device.
Ventilation of a drainage system by a pipe open to the outside air, which can both admit and release air. It is what relieves positive pressure in the below-ground system.
A water source system that abstracts water from a borehole or watercourse, takes heat from it through a heat exchanger, and then returns or discharges it, rather than circulating brine in a sealed loop.
The manufacturer's document telling the user how to run an appliance, what it will accept, how to isolate it and what maintenance it needs.
The document set that explains how a component or system is operated, serviced and fault-found. It holds the fault-finding chart and parts list, and at handover it forms the operation and maintenance manual given to the user.
The file of manufacturers' installation, operating and servicing instructions for every item of equipment, which BS EN 806-5 clause 5 requires to be available, retained and followed.
The checks required by BS EN 14336 clause 5.8 that every component of the system works correctly, made before the system is set to work and balanced.
A person carrying out the work on site. Craft operatives are skilled tradespeople; building operatives carry out labouring and specialist support tasks.
The person or organisation responsible for running a plant, such as a managing agent or facilities manager. Faults that cannot be corrected are notified to them in writing.
A control function that calculates the heat-up time needed and starts the system at the latest moment that still reaches the setpoint at the start of occupancy.
The sequence in which activities must be carried out, because each one depends on those before it.
The compass direction a collector faces. Due south gives the most annual solar energy in the UK.
A bidet filled by taps discharging over its rim, like a basin, so a tap gap protects it and it is treated as fluid category 3. A bidet with an ascending spray or submerged inlet is fluid category 5 and is notifiable.
An injury that leaves a worker unable to do their normal duties for more than seven consecutive days, not counting the day of the accident. It is reportable to the HSE within 15 days.
The full outside area of a solar collector, including its frame. It determines the roof space required and the wind loading, but overstates output if used in the energy calculation.
Protection of a circuit against currents higher than the conductor can safely carry, provided by a fuse or circuit breaker of the correct rating.
The fuse or circuit breaker that disconnects a circuit when the current exceeds a safe value for the cable.
A pipe fitted above the warning pipe on cisterns over 1,000 litres to carry away the full inlet flow if the float valve fails.
The level at which an appliance being filled would start to overflow. Performance tests fill to this level so the discharge is the worst case.
The indirect costs of running a job or a business, such as site offices and site and administration salaries, added as a percentage when a job is priced.
A trap whose outlet leaves horizontally, or nearly so, suiting a branch that runs to a stack on the same level.
Estimating a distance by counting strides of a known length. A rough check only, never a design measurement.
A proprietary unvented hot water storage system supplied with the safety devices factory fitted to the vessel and the remaining controls loose, for the installer to fit.
An energy label produced for a heating system as installed, reflecting the combined performance of the heat pump and its controls rather than the appliance alone.
A booster set assembled and wired at the factory on one skid, with pumps, manifolds, control panel and accumulator, needing only final connections on site.
A prefabricated plant that treats effluent to a higher standard than a septic tank, normally allowing direct discharge to a watercourse.
A pressed steel heat emitter, usually with convector fins welded to the back. It gives most of its output by convection and the rest by radiation.
An absorber in which fluid flows through parallel tubes between two headers, giving balanced flow across the plate. Also called a harp.
An alternative route for the test current, such as bonded pipework, which lowers a continuity reading and can hide a broken conductor. Avoided by disconnecting one end of the conductor under test.
Unwanted gravity circulation of hot water up the vent or draw-off pipe, which drains heat from the store. Also called one pipe circulation.
The section of the Building Regulations dealing with sanitation, hot water safety and water efficiency. Requirement G1 demands wholesome water for drinking, food preparation and washing and water of suitable quality for WC flushing; G2 and Regulation 17K limit new dwellings to 125 litres of water per person per day.
The part of the Building Regulations for England and Wales covering conservation of fuel and power. Northern Ireland uses technical booklet F and Scotland uses section 6.
The manufacturer’s reference for an individual spare part, taken from the parts list in the instructions. When ordering, quote it together with the equipment model number so that the right part for that model arrives.
The part of Schedule 1 to the Building Regulations covering electrical safety in dwellings. It creates the legal duty; BS 7671 gives the technical means of meeting it.
A drainage system that is mainly separate but where the sewerage undertaker permits one or two rainwater connections into the foul drain.
A valve that is passing lets water through when it should be shut — a check valve leaking backwards, or a stopvalve that will not close fully. A float valve that lets by overflows the cistern.
An isolating valve that lets water by when closed, so the gauge falls into an unfilled section as if there were a leak.
A solar thermal system in which the heat transfer fluid circulates by natural circulation, with no pump.
A trap belonging to an appliance that is not being used while another appliance discharges. It is the trap that loses its seal to induced siphonage.
A periodic heating of the whole stored volume to 60 degrees or above to kill legionella, usually driven by a second heat source such as an immersion heater on a timer.
A micro-organism that causes disease, such as the bacteria and viruses found in sewage and animal waste. Any fluid that may contain pathogens is fluid category 5, because a single exposure can cause infection and the organisms multiply rather than dilute.
When and how a household draws hot water across the day. Two homes with the same daily total can need very different systems if one takes its water in a single peak.
The time taken for the savings a system produces to equal the extra cost of installing it. It is shortest where the system displaces an expensive fuel such as electricity, coal or oil.
A published document giving UK guidance on the flushing and disinfection of water services in buildings, complementing BS EN 806-4. It covers the consents needed before disinfectant is discharged to a sewer.
The busiest time of day for the water supply, when the most outlets in the area are drawing and mains pressure is at its lowest. The design pressure for a mains-fed system is the minimum pressure measured at peak demand or given by the water undertaker.
The highest flow rate a system is expected to carry in normal use. Table NG.1 is based on a criterion of satisfactory service of 99 per cent of that loading.
A sum a contract allows to be recovered when work is not completed within the agreed time without agreement to an extension.
A pocket of ground water held above the main water table, the least reliable source because it dries up in a long dry spell.
The statement of expected performance given to the customer before the contract was agreed. It is the reference point against which later claims about performance are judged.
The operational check that measures pressure and flow rate at every outlet against the specification (BS 8000-15 clause 4.5).
The strip of floor next to an outside wall or window where pipes are laid closer together. Its surface may reach 35 °C and its limit output is 175 W/m².
The compressible strip fixed round the perimeter of a heated screed before it is laid, allowing at least 5 mm of expansion. Also called an edge joint.
The level sensing device in a lifting plant that triggers an alarm when the tank contents rise above the working level.
A live conductor that remains energised whatever the controls are doing. It supplies the programmer and any boiler circuit, such as pump overrun, that must work after the switched live has gone.
A formal written authorisation to carry out a defined higher-risk task under stated conditions, used for work such as hot works, confined spaces and work on live services.
Development allowed without a planning application, subject to conditions. Solar equipment has dimensional limits and is excluded on listed buildings.
The repeated need to release gas from the same emitters. It indicates aeration or corrosion in the system rather than ordinary trapped air.
Equipment worn or held by a person to protect them against risks, such as eye protection, gloves, respirators, footwear and harnesses. It is the last resort in the hierarchy.
Everyone who could be harmed by a work activity: the operatives, other trades, the client and occupants, the public, and those who use or maintain the building later.
A scale from 0 to 14 of how acidic or alkaline water is, 7 being neutral. It affects corrosion and how well chlorine works, but it has no direct effect on flow rate and is barely changed by a softener. pH indicator strips change colour to show the value.
A separate technology that converts sunlight directly into electricity using semiconductor cells. It is frequently confused with solar thermal, which produces heat instead.
A tap with a vertical inlet that stands up from the appliance. A high-neck pillar tap raises the outlet so the AUK3 tap gap over a sink is achieved.
A terminal in which the conductor is pushed into a hole in a metal pillar and clamped by a grub screw from the side. Used for the supply cable in a standard fused connection unit.
The centre-to-centre spacing of the underfloor pipe runs, typically 100, 200 or 300 mm. Closer centres give more output per square metre.
A chart or table, published for each pipe material, that relates flow rate, pipe diameter, velocity and head loss per metre, so that any two known values give the other two. It is the reference for the tabular sizing method.
The bracket that fixes a pipe to a wall or joist. Pipework that is insufficiently clipped moves and knocks when a valve closes and becomes noisy at high pressure.
Equipment that forms an ice plug in a pipe so a section can be worked on without draining or isolating the whole system.
A permanently vented backflow prevention device with no moving parts, fitted at least 300 mm above the spill-over level of a WC pan or urinal served by a pressure flushing valve.
A length of pipe between two junctions, numbered from the source, that carries the same flow along its whole length. Each section is sized on the loading units it carries and, for the small sizes, on its length.
A curved fitting on the bottom of a downpipe that throws the discharge away from the wall onto a lower roof or paved area.
A thermostat clamped to a pipe that senses the water temperature inside it and switches the circulating pump. Also called an aquastat.
Equipment that freezes a plug of ice inside a pipe with a refrigerant spray or an electric unit, so that a section can be opened where there is no valve, without draining the whole building.
A level switch on a drinking water header that starts the pumps as the header empties.
Heat given up by the flow and return pipes on their way to the emitters. It is useful where the pipe runs through a heated room and wasted where it runs through an unheated void.
Polyisocyanurate rigid insulation board. It has a lower thermal conductivity than EPS, so about 75 mm does the job of 110 mm of EPS.
A passive infra-red movement sensor that opens a solenoid valve on a urinal supply for a short period when it senses a person.
The angle of a roof slope from the horizontal. It decides the factor applied to the plan area when the effective roof area is worked out.
A drawing that looks straight down on a site, building or room. Block plans, site plans, floor plans and part plans are all plans, each drawn at a scale suited to what it shows.
The area of a roof as seen from directly above, ignoring the slope. It is the starting figure for every effective area calculation.
Maintenance arranged in advance at set intervals to keep a system working, rather than in response to a breakdown.
Maintenance carried out at set intervals to prevent failure, rather than in response to it.
The person responsible for pre-contract planning and for identifying the most economic and efficient use of labour, plant and materials.
Official permission from the local authority for a new building, an alteration or an addition to an existing building.
The machinery and equipment used to carry out construction work, such as access towers, pumps, lifting gear and power tools, whether owned or hired.
The cost of hiring machinery for the days an activity occupies, plus consumables such as blades and discs.
The room in a larger building that houses the boilers, pumps, cisterns, booster sets and treatment equipment. Pipe identification matters most here, where someone years later may add a connection to the wrong pipe.
A water-to-water heat exchanger built from corrugated plates carrying two separated circuits, used in a combination boiler to heat mains water instantly from the primary circuit.
A slug of discharge that fills the bore of a branch pipe completely as it flows. The pressure behind it drops, which is what pulls trap seals out.
A vessel on a booster set holding a small reservoir of water under a cushion of compressed air, which keeps the system at design pressure while the pumps are off.
Testing with compressed air or gas instead of water; not recommended because of the risk of explosion (BS 8558 clause 5.1.9.1).
The point where the undertaker's supply becomes the customer's installation; the supplier is told if disinfectant could reach it.
The device that actually disconnects the circuit being worked on, usually the protective device at the consumer unit. It is the device that gets locked off and labelled.
Backflow protection at or close to an individual fitting or outlet: the tap gap over a basin, a single check valve on each feed to a mixer, a double check valve serving a garden tap. It is the primary protection every outlet must have; zone and whole site protection are added to it, not instead of it.
The correct arrangement of line and neutral throughout a circuit, with every fuse and single-pole switching or protective device in the line conductor only.
A flexible plastics pipe material that expands under test pressure and so needs Test A or Test B rather than the metal one-hour test.
A ground heat exchanger submerged in a pond or lake. It needs a minimum water depth of 3 m and roughly 9 square metres of water surface per kW of output.
Water standing in a low spot in a gutter instead of running to the outlet. It shows the gutter has not been fixed to even falls.
A garden irrigation hose that weeps water along its whole length, also called a permeable or mini-irrigation hose. Because it lies in soil it is fluid category 4 in a house garden, protected by a type DB pipe interrupter in addition to the tap's double check valve, and category 5 elsewhere.
The common connection of a three-port valve, taking the flow from the boiler. Port A serves the heating and port B the cylinder heat exchanger.
An installation where the cistern base is above the shower head and pump, so water flows on its own to lift the flow switch.
A pressure above atmospheric. The air test applies a positive pressure inside the pipework so that any leak pushes air outwards.
A cleaning and flushing procedure using an external pump and tank to circulate water or cleaner at increased velocity and turbulence through the whole system and each radiator in turn.
Acceptance of the works at the end of a project, at which point the building is usable and the defects period begins.
The air pressure put into an accumulator or expansion vessel before it is connected, so the bladder is already under pressure. It must be below the incoming water pressure or the vessel never fills; for an accumulator the usual rule is about half the supply pressure, with a pressure-reducing valve upstream to protect the bladder.
The air pressure in a vessel or accumulator with no water in it, set to about 90 per cent of the pump cut-in pressure.
The inspections and tests in BS EN 14336 clause 5 that bring a system to static completion before it is set to work. They include the state of the system, water tightness, pressure test, flushing, filling and venting.
Information about the site and the project provided by the client to designers and contractors so that risks can be identified and planned for before work begins.
A flush carried out before the chemical clean where a system is heavily fouled, or with a disinfectant where microbiological fouling is suspected.
A list of conditions confirmed before installation begins. Every item is a condition, and its output is a decision on whether work can start.
The check made by the person about to use access equipment, carried out every time and in addition to any formal inspection.
A measure decided at step three of the assessment to remove a hazard or reduce the risk from it before the work is carried out.
The Regulation 5 wording that makes extensions and alterations notifiable everywhere except in a private house.
The work by other trades that must be complete before an activity can start, such as chases, screeds, openings and wall finishes.
A permitted route for a cable buried less than 50 mm deep in a wall: within 150 mm of the top of the wall or of a corner, or running vertically or horizontally to the accessory it serves.
Manufacturer's tables giving the number of turns from closed a valve needs for a given flow rate at a given pressure drop, allowing a circuit to be set without measurement.
A large inlet valve in which a small float-operated pilot valve controls a diaphragm chamber that opens and closes the main valve.
Running a private supply pump from a pressure switch or transducer so it charges an accumulator and the sink can be fed at pressure.
A fall in the manometer reading during the test period. Any steady drop means air is escaping and the system has failed the test.
A sand bed sealed in a cylinder so the supply keeps its pressure through the filter; backwashed like a rapid filter.
A WC flushing device that uses the pressure of water in the supply pipe to compress air, increasing the pressure of the water available for the flush.
A valve that flushes a urinal or WC direct from the supply pressure without a cistern, limited on a urinal to 1.5 litres per flush.
An instrument, usually screwed onto an outside tap, that reads the pressure in the pipe in bar or kPa. Read at a busy time of day it gives the minimum mains pressure for the design.
A coarser pressure control used on stronger stainless steel vessels, set higher than a close-control reducing valve. It is not interchangeable with a reducing valve.
The resistance a pipe offers to flow, in pascals per metre of run. It is read from the sizing table alongside the pipe size and used to work out the pump duty.
A valve to BS EN 1567 that gives a lower, steady downstream pressure by balancing the pressure on a diaphragm against a spring.
The safety valve on a sealed system. Non-adjustable, spring loaded and pre-set to lift at a gauge pressure not exceeding 3 bar, with a manual test device and a full-bore discharge pipe.
A sudden rise in pressure in a pipe caused by water being stopped or started abruptly, for example refilling a drained system with the valves fully open. Refilling slowly, with the stopvalve partly open and the taps cracked open to vent, prevents it.
A switch in which a diaphragm works electrical contacts at a set pressure, used to start and stop booster pumps.
An electronic sensor that turns pipe pressure into an electrical signal a control panel can read, so the panel can start the pumps when the pressure falls.
A section of a tall building served by its own break cistern and pumps, so the pressure on each section stays within the limits its fittings can take.
A valve that lowers the pressure on its outlet side to a set value whatever the inlet pressure. Fitted where the static pressure at an outlet would exceed 500 kPa (5 bar), in the inlet group of an unvented cylinder, and upstream of an accumulator to protect its bladder.
A packaged pump and vessel assembly that fills a large sealed system and maintains its pressure automatically, used instead of a filling loop.
The pipework between the heat source and the manifold, carrying water at the heat source temperature before it is blended down.
The flow and return between the heat source and the things it serves, such as the cylinder coil and the underfloor manifold. Its heat cannot be switched off by a room control.
Pipework carrying water between the heat source and the emitters or the cylinder coil. Part L sets where and how it must be insulated.
A layout in which appliances are closely grouped around one discharge stack and the stack, extended to atmosphere, provides all the ventilation. Formerly called the single stack system.
The water circulating between the heat source and the heat exchanger. It is never drawn off at a tap, so it may be treated with inhibitor in a double feed system.
The actual cost of the labour, materials and plant used on a job, before overheads and profit are added.
Filling a pump body and its suction pipe with water to drive out the air so that the impeller can move water. An air-locked pump is primed through its priming plug with the suction valve opened first.
The contractor appointed to plan, manage and monitor the construction phase where there is more than one contractor. It prepares the construction phase plan, provides welfare and ensures site inductions are given.
The duty holder appointed to plan, manage and monitor the pre-construction phase, advising and assisting the client and team with their health and safety responsibilities.
The printed marking running along the length of a plastic pipe. Watching whether it stays straight tells you if the pipe has twisted as it comes off the coil.
The board on which manufacturers mount the electronic components that control an appliance.
A design in which one circuit, usually the hot water cylinder, is served before the other, so heating is suspended while the cylinder reheats.
An individual who engages a plumbing firm directly for work on their own property, such as a homeowner or a landlord.
Installation work carried out for a private customer in their own property, such as replacing a bathroom with a wet room.
Water from a source other than the water undertaker, such as a borehole, well or spring. Where it shares a building with the mains it is treated like any other non-wholesome fluid: entirely separate pipework and clear identification.
The regulations that set the quality standards for water not supplied by a water undertaker and require each supply to be risk-assessed, sampled and tested by the local authority. England had the 2009 Regulations, replaced by the 2016 Regulations; Wales has its 2010 Regulations.
The regulations that govern private supplies in England, enforced by the local authority through risk assessment, sampling and notices.
Any water supply not provided by a water undertaker: a borehole, well, spring, stream, river, lake or pond serving one house or a small private network. The owner or user is responsible for it, the Water Fittings Regulations do not apply to it (apart from the ban on cross-connection to a mains supply), and its quality is policed by the local authority under the Private Water Supplies Regulations.
The proportion of the price that remains as profit once the costs of the work have been met.
A single unit that holds a time schedule and senses room temperature, providing time and temperature control together.
The person or organisation responsible for the overall work programme on a project, normally the principal or main contractor.
The time control that decides when the hot water and heating circuits call for heat. Faults include a lost or wrong time setting, failed boost functions and failed switching.
The person responsible for the overall co-ordination and delivery of a project and for ensuring the project team works together effectively.
The spreading of a fixed amount of radiation over a larger area as a surface is tilted away from the beam, reducing the energy received per square metre.
A glycol used as a heat transfer fluid. It is much less toxic if swallowed than ethylene glycol, which is why it is normally specified near domestic water supplies.
The wrapping or tape fitted to a sanitary appliance to guard it against damage on site. It is kept in place as long as practically possible, up to handover.
The fuse or circuit breaker protecting the circuit. Commissioning verifies that it is of the correct type and rating for the circuit and the appliance.
A small battery-powered source of a known voltage used to prove that a voltage indicator is working, both before and after testing a circuit dead.
Regulations setting minimum standards for work equipment: it must be suitable, fit for purpose, maintained, guarded and used only by people who have been trained.
The regulations governing work equipment. They require equipment to be suitable, maintained and inspected, and everyone who uses it to have had adequate training.
The factory-assembled module carrying the manifold circulating pump and blending valve, which mixes and circulates water to the floor circuits.
The manufacturer's chart of the flow a pump delivers against the head it develops, usually with one curve per speed setting.
The run of a macerator from starting on a discharge, through shredding and pumping, to stopping when the chamber is empty. It is timed at commissioning as a baseline.
A booster pump switching on and off repeatedly because every small draw-off drops the pressure enough to start it. It wears the pump and the switch; an accumulator stores enough water to cover small draw-offs and stop it.
The pipe on the outlet side of a pump. Schedule 2 paragraph 14 names it alongside supply and distributing pipes as a pipe that must never be able to convey non-wholesome water.
The flow rate and pressure a pump must deliver, found from static lift, friction losses and residual pressure.
A boiler circuit that keeps the pump running after the burner has shut down so that residual heat is carried away from the heat exchanger.
A fault in which the pump forces water up the open vent and into the feed and expansion cistern, aerating the system water and causing corrosion.
The document by which a company formally orders goods from a supplier at an agreed price and delivery date.
A powered pump and tank unit connected to a filled circuit to circulate the fluid at high velocity, sweeping trapped air out of pipework that cannot be vented from a high point.
A hybrid collector that produces both thermal energy and electricity from one panel.
Ranking a risk by placing it in a category such as low, medium or high rather than on a long numeric scale.
Ranking a risk with a number, using scales for likelihood and consequence and multiplying them together.
The construction professional who measures and prices building work, prepares the bill of quantities from the architect's drawings and controls the cost of a project.
A tap opened fully by a quarter turn of a lever, needing a push rather than a grip and so suited to users with limited hand strength.
A fixed price offered for a described piece of work; once accepted it cannot be increased without agreement. It is one of the two things, with the drawings, a client needs before work starts on a dwelling.
The combined resistance of a circuit's line conductor and its circuit protective conductor, measured with the two linked at the origin and read at the far point of the circuit.
The rate at which rain falls, in litres per second per square metre. It is taken from a local map or, where no data exists, from the minimum values in BS EN 12056-3 multiplied by a risk factor.
Collecting rain from roofs, storing it and pumping it to WCs, washing machines and gardens in place of mains water. The water is not wholesome, so the pipework must be identified and kept separate from the mains, and on a mains-fed site the water supplier is notified before work starts (BS 8515).
The vertical pipe carrying water from a gutter outlet to a drain or gully. In domestic round systems it is 68 mm; the square section equivalent is 65 mm.
Risk assessment and method statement. Internal documents about how work will be carried out safely, not part of the customer's handover pack.
Several appliances of the same kind connected in a row to one common branch discharge pipe, such as a line of basins in a washroom.
A physical filter of coarse silica sand, 0.5 to 1 mm, that removes turbidity, algae, iron and manganese and is cleaned by backwashing. The preferred sediment removal on a small supply.
Sizing a cistern so the stored water is used and replaced quickly, so it does not stagnate.
Putting a repaired section back into service: refilling slowly from the service stopvalve, venting, flushing, pressure testing altered pipework at 1.5 times working pressure, disinfecting where needed, then re-checking pressures and flows against the record and inspecting for leaks.
Changing the order or timing of activities on a programme so that the work can carry on after a delay.
A legal test in which the size of a risk is weighed against the time, trouble and cost of controlling it. The control must be taken unless it is grossly disproportionate to the risk.
Water that is not wholesome but is put to use, such as harvested rainwater or treated greywater; also called recycled or non-wholesome water. BS 1710 identifies its pipes with green, black, green colour bands.
The as-installed drawing kept in the building log book. Every repair coupling in a floor construction must be located and designated on it.
The rate at which a heating source can bring stored water back up to temperature, expressed either as litres per hour at a stated temperature rise or as the time to reheat the vessel.
The time allowed for a hot water cylinder to reach its storage temperature from cold. Shortening it sharply increases the kilowatts required.
A verifiable backflow preventer with two check valves, a differential relief valve between them and three test points; the middle chamber is held below supply pressure and is dumped to drain if the pressure difference falls or a check valve leaks. Rated fluid category 4 for both back pressure and back siphonage, the highest of any mechanical device. It is notifiable, needs a line strainer, servicing valves and a tundish to a type AA air gap 300 mm above the floor, and is tested annually by an accredited tester.
A planted bed through which greywater infiltrates. Oxygen from the reed roots supports bacteria that break down organic matter. It needs land and expertise.
The room whose thermostat acts as the main temperature control for a heating circuit, and in which no other form of system temperature control is fitted.
A joisted underfloor system where the pipe sits above a reflective foil layer instead of in a metal plate. It relies on a still layer of air below the boards.
A hand instrument that measures the concentration of a mixture from how it bends light. It is used to confirm the antifreeze strength in a collector.
The working fluid of a heat pump. It evaporates at low pressure while absorbing heat from the source, is compressed to raise its temperature, and condenses to release that heat into the heating system.
The vapour compression cycle used by a heat pump: evaporate, compress, condense, expand. It moves heat from a cold place to a warmer one using work from a compressor.
The card carried by an operative registered to work on unvented hot water systems. Its number is entered on the commissioning record and on paperwork sent to the local authority.
A valve on a floor branch used to throttle flow during balancing so that other outlets receive their share.
The regulation that sets out the five harms (waste, misuse, undue consumption, contamination and erroneous measurement) and forbids anyone to install, alter, disconnect or use a water fitting in a way that causes or is likely to cause them. Regulation 3(3) adds that no damaged, worn or faulty fitting may be used, so it binds users as well as installers.
The regulation that sets the two quality tests for water fittings, appropriate quality and standard and suitability for the circumstances, and requires installation in a workmanlike manner. Regulation 4(2) says quality is shown by a British Standard or a regulator-approved specification; 4(5) and 4(6) define workmanlike work.
The part of the Water Fittings Regulations that lists the operations for which the water undertaker must be notified before work starts: erecting a building, extending or altering a water system anywhere other than a house, a material change of use, a bath over 230 litres (to the centre line of the overflow), a bidet with an ascending spray or flexible hose, a pump drawing more than 12 litres a minute, reverse osmosis, a water treatment unit with a waste or needing regeneration, an RPZ valve or other device for fluid category 4 or 5, an automatic garden watering system, pipe laid outside a building less than 750 mm or more than 1,350 mm deep, and an automatically refilled pond or pool over 10,000 litres. The notice must give names, addresses, a description of the work and the premises, and usually a plan and pipework diagram.
The regulation requiring an approved contractor, on completing work, to give a signed certificate of compliance to the person who commissioned it and, where the work was notifiable, to send a copy to the water undertaker.
In the Water Fittings Regulations, the Secretary of State for England and the Welsh Ministers for Wales, not Ofwat. The regulator approves specifications that count as appropriate quality, specifies the bodies that can certify approved contractors, and is the only person who can relax a Schedule 2 requirement, on an undertaker's application.
The time taken to bring a cylinder from cold, or from a drawn-down state, back to its storage temperature. It is set by the energy needed and the power the coil can pass.
The discharge opening on an RPZ valve through which the relief valve dumps water when the pressure in the middle chamber gets too close to the inlet pressure. A port that keeps dripping points to a failed upstream check valve or a ruptured diaphragm.
The manufacturer's schedule of the components of an appliance that can be replaced, each with a part number to be quoted alongside the model number when ordering.
The formal route through which an operative takes instructions and reports problems, normally to their own supervisor.
Regulations requiring the employer to record and report certain work-related deaths, injuries, diseases and dangerous occurrences to the enforcing authority.
The regulations requiring specified injuries, occupational diseases and dangerous occurrences to be reported to the enforcing authority.
The internal request from site to the company for materials or plant, giving quantities, sizes and the date they are needed.
A trap designed for unventilated small bore branches that restores its own water seal after siphonage. Anti-vacuum traps do a similar job by admitting air.
The small amount of disinfectant, such as chlorine, left in the water after treatment to go on protecting it in the pipes. UV leaves none.
Stored electrical energy remaining in components after isolation, which must be allowed to discharge for the time the manufacturer states before work begins.
The free chlorine left at the end of the contact time, measured at the furthest outlet; not less than 30 mg/l is a pass.
A device that compares the current flowing out along the line conductor with that returning in the neutral and disconnects quickly if the difference shows current leaking to earth.
The chlorine or bromine left in the treated water after disinfection. BS 8525-2 sets limits on it for each end use.
The pressure left at the end of a pipe section after the rise and the friction losses have been taken from the available head. It must be at least what the outlet or appliance needs, or the pipe goes up a size.
The pressure still needed at the outlet after static lift and friction have been overcome, so the tap or float valve works properly.
The risk that remains after all the chosen control measures have been applied. It must be small enough to accept and must be made known to those doing the work.
A fixing made by injecting a two-part resin into a drilled hole and setting a stud into it. Eye protection is required because the resin is ejected under pressure.
The person accountable for the building or the system, such as the householder, the landlord or a site manager, who must be kept informed of isolations.
The large radius bend at the foot of a discharge stack where it turns into the drain, with a centre line radius of at least 200 mm.
A ring that holds a shower hose so the head cannot reach below the rim of the bath.
Repeating a test after a defect has been corrected; nothing is handed over until the retest passes.
Installing a system into an existing building. Retrofit work is harder than new build because the building, the drainage and the occupants are already there.
The average interval between storms of a given severity, used to set how heavy a rainfall a system is designed for. A one in ten year return period means a storm of that size is expected on average once a decade.
A self-acting control on a single-zone underfloor circuit that throttles flow when the return water is too hot, holding the floor temperature down without room-by-room control.
Treatment that forces water through a semi-permeable membrane to remove salts, nitrates and pesticides, wasting about 3 litres per litre made. Notifiable under Regulation 5.
A two-pipe variation in which the return runs away from the boiler alongside the flow before looping back. Total circuit lengths are almost equal, so the system is close to self-balancing.
A valve that reverses the direction of refrigerant flow so the roles of the evaporator and condenser swap. It is used for defrosting and, on reversible units, for cooling.
The planned or triggered re-examination of a risk assessment to check that it still describes the work, the place and the people, and to update it where it does not.
An employee's right to be accompanied at a formal disciplinary or capability meeting, normally by a colleague or trade union representative.
Metal pipework such as copper, stainless steel and low carbon steel that does not stretch appreciably under pressure, so any fall in the gauge means a leak.
A final circuit wired as a ring serving socket outlets, protected by a 30 A or 32 A device under BS 7671.
A pre-use check on an abrasive wheel: the wheel is tapped with something non-metallic and listened to. A sound wheel rings clearly and a cracked one sounds dull.
The supply pipe that rises through a building to feed a storage cistern or high-level outlets.
The chance that somebody could be harmed by a hazard, together with an indication of how serious that harm could be.
A written review of what could go wrong, how likely it is and how serious it would be. Every private water supply must have one covering the source, storage, treatment and premises, and Approved Document G requires one before an alternative (non-mains) water source is used in a dwelling.
The pair of documents normally issued together for a job: the assessment identifying the hazards and controls, and the statement setting out the safe sequence of work.
The standard document a company uses to record an assessment, with columns for the hazards, the harm, the people at risk, existing controls, the rating and the further action.
A method of ranking risk by multiplying likelihood by consequence to give a number that quantifies the level of risk for a particular job.
The number produced by multiplying likelihood by consequence, used to place the risk in a band that determines the action required.
An access fitting on discharge pipework or a stack that allows rods to be passed into the pipe to clear a blockage.
A control that senses the air temperature of one room and calls for heat. Mounted about 1.5 m above the floor away from sunlight, draughts and other heat sources.
The underlying reason a fault occurred, as opposed to the part that failed. Curing only the failed part leaves the fault to return.
A mechanical backflow prevention device with two check valves and a relief valve between them that opens to drain if the pressure in the middle zone rises towards the inlet pressure, so backflow can never reach the supply. It is the highest mechanical protection, used against fluid category 4, must be tested annually by an approved tester, and is notifiable under item 4(g).
Water drawn from an outlet and sent straight to drain, such as a tap left running or water run off while waiting for hot to arrive. Limiting it, for example with flow regulators or self-closing taps, deals with the undue consumption part of Regulation 3.
The ongoing cost of fuel, electricity and maintenance once a system is installed, as distinct from the capital cost of installing it. Micro-renewable systems trade a high capital cost for a low running cost.
Operating a pump with no water passing through it, so the bearings and seal lose their lubrication and cooling and are damaged.
An outlet fitted part way along a gutter run, receiving water from both directions. It can drain almost twice the area of an outlet at a stop end.
A factor in the flow equation allowing for water that does not reach the gutter. It is taken as 1.0 unless national or local practice states otherwise.
A fully pumped heating system with a separate two-port motorised zone valve on the hot water primary and on the heating circuit, each opened by its own thermostat.
An S-plan with an additional two-port zone valve, so the space heating is divided into two independently controlled zones as well as the hot water.
A rod of a more reactive metal fitted inside a storage vessel. It corrodes in preference to the vessel, protecting it.
The procedure for making electrical equipment safe to work on: switch off, lock off the isolator, prove the circuit dead with a voltage indicator that has itself been tested, and label it. Every electrical test on a pump or panel follows it.
A formal procedure resulting from an assessment of a task, which identifies the hazards and defines the method and controls to be used so that the work is done safely.
The manufacturer's sheet for a chemical that states its hazards and the PPE required to handle it.
A device that protects the user and acts only when the functional controls have failed. On an unvented system the two Approved Document G requires are the non-self-resetting thermal cut-out and the temperature relief valve. The expansion relief valve does a safety job against pressure, though it is listed with the functional controls.
A body harness attached to an anchor by a lanyard, used as a last resort to restrain a person from a fall zone or to arrest a fall. Used only by trained people and inspected before and after every use.
The set of arrangements, procedures, records and checks a business uses to manage health and safety, and to show that it has done so.
A short written notice issued to everyone affected, recording a safety message such as a newly found hazard or a change to site arrangements.
The spring-loaded valve that opens automatically if the system pressure exceeds its setting, releasing water safely. On domestic sealed systems it is set at not more than 3 bar.
A fitting that takes a water supply and discharges to drainage, such as a bath, shower, washbasin, sink or WC. The number and type of these sets the demand on a hot water system.
In the Building Regulations, a closet or a urinal. Every sanitary convenience must have an associated hand washing facility.
The above ground pipework that carries discharges from sanitary appliances to the drain. It covers traps, branch discharge pipes, stacks and ventilating pipes.
A burn caused by hot water or steam. Water at 60 degrees C can cause a partial thickness burn in about five seconds, which is why outlet temperatures are limited.
Hard deposit, mainly calcium carbonate, that forms out of hard water on the hottest surfaces of a system. It insulates heating surfaces and narrows pipe bores.
A drawing in which every length on paper is a fixed fraction of the real length, so distances can be measured off it: at 1:50, 10 mm on paper is 500 mm in the building; at 1:100 it is 1 m; at 1:500 it is 5 m. A not-to-scale sketch shows what goes where but cannot be measured.
A ruler with several scales marked along its edges, such as 1:50 and 1:100, so a real length can be read directly off a scale drawing. Pick the edge that matches the drawing's scale; reading the wrong edge is the commonest mistake.
The part of the Water Supply (Water Fittings) Regulations 1999 that defines the five fluid categories, from category 1 (wholesome water) to category 5 (serious health hazard).
The part of the Water Fittings Regulations that holds the technical requirements, in numbered paragraphs: materials and substances (2 to 7), design and installation (8 to 13), backflow prevention (14 and 15), cisterns (16), WCs and urinals (25) and water economy (29), among others. Being part of the Regulations it is law, and where the guidance and Schedule 2 differ, Schedule 2 governs.
The requirement that every supply or distributing pipe to separate premises has a stopvalve that shuts off that supply without shutting off any other premises, and that every occupier of a shared pipe has access to a stopvalve.
The requirement that water systems can be drained down, with enough servicing valves and drain taps to minimise the water discharged when fittings are maintained or replaced, and enough stopvalves to isolate parts of the pipework.
The Water Regulations requirement that a water system withstands an internal pressure of not less than 1.5 times the maximum pressure it is designed to work at, together with the descriptions of the tests that satisfy it.
The paragraph of the Water Regulations requiring every water system to be tested, flushed and where necessary disinfected before first use.
The rule that any water fitting carrying rainwater, recycled water or any fluid that is not wholesome must be clearly identified so it cannot be mistaken for a supply or distributing pipe, and that no supply, distributing or pump delivery pipe may convey, or be connected so that it can convey, such a fluid, unless a backflow device meeting paragraph 15 is fitted.
The requirement for a servicing valve on the inlet of every storage or flushing cistern and on the outlet of every storage cistern.
The paragraph of the Water Fittings Regulations that forbids a permanent connection between a primary heating circuit and the supply pipe unless an approved backflow prevention device is fitted.
The paragraph of the Water Fittings Regulations on WC and urinal flushing. Paragraph 25(1)(b) bans a pressure flushing valve in a house or where 1.2 litres per second is not available, and 25(1)(c) requires the type DC interrupter not less than 300 mm above the spill-over level.
The Water Regulations requirement that every water fitting is of an appropriate quality and standard, suitable for the water and conditions it meets, and immune to or protected from corrosion by galvanic action.
The list in the Building Regulations of minor work that need not be notified to building control at all: replacing part of, or adding a control to, an existing cold water supply, or replacing a WC, basin, sink, bath or shower with one that uses no more water, provided no underground drainage or health-affecting work is involved. The requirements still apply; only the need to notify is removed.
The list of inspected items issued alongside an Electrical Installation Certificate or a condition report. It does not form part of a minor works certificate.
A list of agreed unit prices for defined operations, used where the type of work is known but the quantity is not. Work is measured on completion and paid at those rates.
The record of the measured values from inspection and testing: continuity, insulation resistance, polarity, earth fault loop impedance and RCD results, issued with the certificate.
A line drawing of the pipework itself, showing every pipe, junction, valve and appliance in order but usually not to scale. It is the drawing used to explain how a system works and, with its junctions numbered, to lay out a pipe sizing calculation.
A drawing that shows how a system connects and in what order, without representing true position, scale or route.
The tyre-type air valve on an accumulator or expansion vessel through which the air charge is checked and topped up.
What the contract requires the team to do, and the constraints it must work within. A variation changes the scope.
The layer of cement, calcium sulphate or asphalt laid over the underfloor pipes, forming the heat-conducting mass and the load-bearing surface.
The layer of grease and light material that floats on the surface of a septic tank and must not be disturbed by the inlet or outlet.
A heating circuit that is closed to the atmosphere and pressurised, with an expansion vessel instead of a feed and expansion cistern. Its connection to the supply pipe is a backflow risk: a temporary filling loop through a double check valve in a house, or a permanent connection through a type CA (category 3) or type BA (category 4) device.
A heating circuit with no feed and expansion cistern or vent, filled through a filling loop and using an expansion vessel. It is separate from whether the hot water is vented or unvented.
A heating system with no feed and expansion cistern, filled from the mains through a filling loop, with expansion taken up in a diaphragm expansion vessel and protected by a pressure relief valve.
The annual quantity of heat delivered divided by the annual electrical energy consumed. It reflects real performance across a heating season.
The average efficiency of a heat pump across a whole year, taking in all its operating conditions. Running frequent high temperature hot water cycles pulls the SPF down.
The stage when accessories and equipment are fitted and cables are terminated, after the building finishes are complete.
A pumped loop that returns hot water from the far end of the distribution pipework to the storage vessel, keeping the pipework hot and removing the dead leg.
The hot water draw-off pipe carrying water out from the storage vessel to the outlets on a circulating system.
The pipe carrying circulated hot water back from the far end of the distribution system into the storage vessel.
A layout with closely grouped appliances in which a separate ventilating stack is cross-connected to the discharge stack to control pressure within the stack.
The stored water in the cylinder that is drawn off at the hot taps. It must remain wholesome, so nothing may be added to it.
A drawing that cuts vertically through a building to show what is inside: floor-to-floor heights, the loft, the thickness of floors and the position of a cistern. It gives the vertical rises a floor plan cannot.
Testing a completed part of an installation on its own, rather than the whole system, because of its size or because that part is about to be enclosed.
A large cistern bolted together on site from 1 square metre GRP or protected steel panels, so it can be built to any capacity and to fit the space.
Seated and inactive. A sedentary occupant gives off less heat than an active one, so activity level affects the heat gains allowed for in a design.
A tap or draw-off that is rarely run, flushed weekly under BS EN 806-5 clause 6 so water does not stand in its branch.
An absorber coating that decreases radiative emission from the plate while keeping a high absorptance for solar radiation, so the plate holds the heat it gains.
Loss of a trap seal caused by the appliance's own discharge filling the branch pipe and drawing a partial vacuum behind the moving water.
A booster set built on site from separately bought pumps, valves, switches, vessel and controls, for which the installer matches and sets the parts.
Certifying your own work as compliant instead of having it inspected. Under the Water Fittings Regulations an approved contractor does this with a certificate of compliance; under the Building Regulations a competent person scheme member does it under Schedule 2A.
A pipe laid so that the flow through it scours the bore and carries solids away, rather than letting them settle.
The flow speed a waste pipe needs to carry solids away; the small discharge from a self-closing tap may fall below it.
Trace heating cable whose output rises where the pipe is cold and falls where it is warm, so it cannot overheat any part of the run.
A waste valve that replaces a water trap with a flexible membrane. It opens to let waste out, closes when flow stops, and stays tightly closed under back pressure.
Loss of the seal from the trap of the appliance that is discharging, caused by the vacuum behind a plug of water running full bore in the branch.
A heating system with a pumped heating circuit and gravity-circulated hot water primaries, usually in 28 mm pipe. Now regarded as a system to upgrade.
Heat that changes the temperature of a substance and can be measured with a thermometer. A person at rest gives off about 115 watts of it.
The small cable carrying the signal from a temperature sensor back to a controller. It works at extra-low voltage and carries almost no current, but is sensitive to interference and to its environment.
The infra-red emitter and receiver on a sensor tap that projects a beam of 200 to 260 mm and signals the solenoid when it is broken.
A below ground drainage arrangement with two sewers. The foul water is treated and the surface water is discharged untreated to a watercourse or soakaway.
Parts of one building or site occupied by different people or businesses, such as flats fed from a common supply pipe or units in a shared building. Schedule 2 paragraph 15(4) requires backflow protection where necessary to stop backflow passing between them.
A multi-chamber underground tank in which solids settle and partly decompose, and the separated liquid passes on to secondary treatment.
The order in which the stages of a job are carried out, set so that each stage leaves the site safe for the next and so that trades are not put at risk by each other.
An underfloor pipe layout running back and forth across the room at set centres, with the flow taken first to the coldest part. Also called the meander or serpentine pattern.
An absorber in which a single continuous S-shaped tube carries the fluid across the plate, lengthening its path.
An agreement to keep a building's plant and systems functional, safe and in working order over a period, through scheduled visits and agreed response times.
The record of what has been done to a system since it was commissioned, including dates, tests, readings and parts replaced. It shows whether a fault has occurred before and how the system has been drifting.
The pipe from the water main to the building, made up of the undertaker’s communication pipe and the customer’s supply pipe. A service pipe unused for a year or more should be disconnected from the main.
The written record of a maintenance visit, giving the date, location, tests performed, readings taken and parts replaced. BS EN 806-5 requires it to be stored so the data is auditable.
The manufacturer's list of the checks a particular appliance needs and the interval at which each is due.
A point where two trades' installations are shown in the same place on the drawings, so one of them has to move.
The free space that must be left around an appliance so that routine maintenance can actually be carried out and the appliance can be removed and replaced.
A small isolating valve fitted close to an appliance or float-operated valve so it can be shut off for repair without draining the system. Schedule 2 requires one on the inlet to every cistern, and one upstream and downstream of every category 4 mechanical backflow device.
The first stage of commissioning, in which the system is started up and run for the first time under its designer's intended conditions.
A tank fed from the intake where suspended solids drop out before the water goes on to the filters, with a raised, screened outlet.
The company responsible for the public sewers in an area, usually the same company as the water undertaker. It must be told and give approval before used disinfectant is discharged to a drain or sewer, and may require the disinfectant to be neutralised first.
Obstruction of the collector by trees, chimneys, aerials or other buildings. It removes radiation outright and is worst in the spring and autumn months.
The outer covering of a cable. It holds the cores together and provides mechanical protection; it is not the insulation and is not a conductor.
A vessel with a piston or diaphragm cushioned by inert gas or air that absorbs the energy of a water hammer wave.
A pump starting and stopping repeatedly at short intervals, which the pressure vessel is fitted to prevent.
A greywater system that skims debris and lets particles settle, stores a small volume, and purges it if it is not used within about 24 hours.
Water passing straight from inlet to outlet without flowing through the whole cistern, leaving the rest to stagnate.
Spring and autumn. The sun is low, shadows are long, and these months carry a large share of the annual solar yield.
A pump fitted to a gravity shower that has less than about 1 m of head, to raise the pressure at the shower head.
A preformed sloping panel set into the floor of a wet room that builds in the fall to the outlet. On solid floors a screed can do the same job.
The flexible hose between a bath mixer and a hand-held shower head. If it can lie below the bath's spill-over level the head becomes a submerged outlet and the tap gap is lost.
A pump that circulates water within a large storage vessel during periods of low demand, evening out the temperature so no cool layer is left for bacteria to grow in.
A small window in the liquid line that shows the state of the refrigerant. Clear liquid is normal at steady state; persistent bubbles suggest undercharge or non-condensables.
The signatures recording that the assessment was completed, checked by the supervisor and approved, each with a name and a date.
The important hazards, the people at risk and the control measures, which are what a written risk assessment has to record.
The figure taken as the outcome of a repeated test. For performance testing it is the maximum loss of seal measured in any one of the repeats.
The BS EN 806-3 pipe sizing method used for dwellings and similar buildings: starting at the last draw-off point, add the loading units section by section back to the source and read the pipe size for the material from Table 3, which builds in simultaneous demand and limits the length of the smaller sizes.
The flow a pipe has to carry when several of the outlets it serves are in use at once. Not every outlet is used together, so the loading unit tables build in an allowance, sometimes called diversity, rather than adding every design flow rate.
Discharging two or more appliances at the same moment, as a performance test requires, so the pipework sees the flow it would at peak use.
A spring-loaded one-way valve that lets water flow downstream only and closes when flow stops or reverses. Type EA has a test point, type EB does not. Rated fluid category 2 both ways; used on each feed to a mixer, in the inlet group of an unvented cylinder and on each pump outlet in a booster set.
A shower pump with one impeller fitted on the outlet of the mixer to boost the blended water.
A pump fitted after the shower mixing valve that boosts the mixed water to the outlet. Also used to boost an individual hot or cold outlet.
A house occupied by one family. New installations and major extensions in one are flushed but not usually disinfected; the exception does not cover suspected contamination.
An electrical supply from one live conductor and a neutral at 230 V, as in a house. A single-phase pump motor needs a capacitor to start and run; three-phase motors do not.
A motorised grinder fitted under a kitchen sink that reduces food waste to a paste and flushes it to the drain through a 40 mm waste.
A valveless flushing device that starts the flush by lifting water over a weir into the down leg. It cannot leak past a seat, but it needs physical effort to operate.
A WC pan that clears its contents by setting up a siphon in the trapway, so a difference in air pressure draws the contents out.
A pan with a double or restricted trapway that fills on flushing and starts a siphon, which pulls the contents out.
The physical circumstances of the site: ground conditions, access, storage, occupancy and anything else that limits how and when work can be done.
The daily record kept on site of what happened, including weather, stoppages and visitors, used as evidence if a delay is disputed.
A site-based engineer responsible for setting out the works and controlling levels so that the building is constructed in the correct position.
The briefing every person receives before first working on a site, covering the site's hazards, rules, traffic routes, welfare facilities and emergency arrangements.
A written instruction issued on site telling the contractor to do something differently. It is one of the acceptable written forms for instructing a change.
The people responsible for running the site day to day, to whom the trade supervisors report and who co-ordinate the trades against the programme.
A plan of the building on its plot, usually at 1:500 or 1:1000, showing the incoming main, the boundary stop valve for each dwelling, the drains and any external pipe runs. It is where the connection point for each dwelling is found.
The state of the building's preparation for a following trade: whether the preceding work, openings, fixings and finishes needed are actually complete.
The building contractor's main representative on site, responsible for the day-to-day running of the site including budgets, staffing and deliveries. Also called the construction manager or project manager.
The visit at which the building, its services and its surroundings are measured and assessed against the conditions a proposed installation needs.
An assessment written for one job at one location, taking account of the actual hazards, people and conditions found there.
A tube built into an opening through which a pipe passes, allowing movement and protecting the pipe from the structure.
A continuous overlapping coil of collector pipe laid in a trench, so that more pipe fits into each metre of trench.
The amount by which an activity is behind the date the programme shows for it.
A filter of fine sand, 0.15 to 0.30 mm, on which a biological layer removes micro-organisms; cleaned by scraping the top layer.
The settled solids at the bottom of a septic tank. Most is removed when the tank is desludged, but some is left as an anaerobic seed.
Conventional domestic heating pipework, typically 15 mm to 28 mm, run as a two-pipe circuit and sized to a maximum velocity of about 1 m/s.
A heating system whose circulation pipework is normally 15 mm to 35 mm outside diameter. The ordinary domestic two-pipe system is smallbore.
The equipment that generates smoke under pressure for a smoke test, as an alternative to a chemical smoke cartridge.
A leak location method in which smoke is introduced into pressurised pipework and leakage is seen where it escapes. It must be avoided on plastics.
Identifying and listing defects or unfinished items so that they can be put right before the work is accepted.
The list of outstanding items and defects recorded at inspection, to be corrected before work is fully accepted.
An underfloor pipe layout spiralling inward and returning between its own runs, so flow and return alternate and the surface temperature is very uniform. Also called bifilar or spiral.
A pit or trench that lets collected surface water infiltrate into the ground rather than run to a sewer or watercourse.
Sodium carbonate crystals dissolved in hot water to clear grease and soap residues from waste pipes. They are not caustic soda, which must not be used for this purpose.
The usual chlorine disinfectant, to BS EN 901; at 5 per cent available chlorine, 1 litre per 1,000 litres of system water gives 50 mg/l.
The discharge from WCs and urinals, containing human waste. It is kept separate in design terms from waste water, which is the discharge from basins, baths, showers and sinks.
The combined effect of air temperature and solar radiation on a surface. It explains why a building gains heat from sun-warmed surrounding air as well as from direct sunlight.
The panel or tube array that absorbs solar radiation and passes the heat to the transfer fluid. Made as a flat plate or as evacuated tubes.
The share of the annual hot water demand met by the solar system. A well-designed UK system achieves about 60 per cent.
Heat gained from direct sunlight through glazing and onto the fabric. It varies with orientation, season and time of day, and is largest on south-facing surfaces.
The solar energy falling on a surface over a period, measured in kilowatt hours per square metre. It varies with orientation, tilt, location and shading.
Silicon cells that convert solar radiation directly into d.c. electricity. Entirely different from solar thermal despite looking similar on a roof.
The role solar thermal plays in a hot water system. It raises the temperature of the store as far as the sun allows, leaving the auxiliary source to make up the rest.
A system that uses solar radiation to heat a fluid in a roof collector, and transfers that heat to stored hot water. It produces heat only.
The gradual flow of solder under the pressure of a clamped joint, which loosens a connection over time. It is why tinned conductor ends are not permitted in screw terminals.
An electrically operated valve in which an electromagnet lifts a plunger to open the valve and a spring closes it when the coil is de-energised. On a cistern it is signalled by a float switch.
A jointing method for plastic pipe in which cement chemically fuses the pipe and fitting. It is the only plastic jointing allowed on macerator discharge pipework.
A measure of the acoustic energy a unit emits, quoted on the energy label. It is a property of the machine, and is used with distance and siting to judge the noise a neighbour will actually hear.
The pressure test that proves the pipework will hold water at more than its working pressure without leaking, required by Schedule 2 paragraph 12.
Testing an installation for leaks under pressure, in accordance with the procedure named in the specification.
The convention by which heat pumps are named: the first word is where the heat is collected from, the second is what the heat is delivered into. Ground-to-water collects from the ground and heats a wet system.
A part of a dwelling served by its own heating circuit with its own time and temperature control, normally through a motorised valve driven by a thermostat.
The perforated pipe along the top of a slab urinal that spreads the flush water down the wall. Older guidance placed the pipe interrupter 150 mm above it; the Regulation figure is 300 mm above the spill-over level.
For Part P, the zone around a bath tub or shower tray, extending to 2.25 m above floor level and 0.6 m horizontally, or a room containing a swimming pool or sauna heater. A kitchen is not one.
The energy needed to raise one kilogram of a substance by one degree. For water it is about 4.18 to 4.2 kilojoules per kilogram per degree.
The heat that can be taken from each metre of collector, or each square metre of ground, without the ground cooling out. Quoted in W per metre or W per square metre.
The design document giving pipe sizes, materials, storage volumes, pump duties and design pressures. A component that does not match it is reported to the manager.
The level at which water would run over the rim of an appliance, cistern or vessel. Every air gap is measured vertically from the lowest point of the outlet down to this level.
The level at which an appliance would overflow, normally the top of its overflow or the rim. Rodding points and branch vent connections are taken above it.
A heat pump split between an outdoor unit and an indoor unit, with refrigerant pipework between them, so system water stays inside the building.
A heat pump with the evaporator outdoors and the condenser indoors, joined by refrigerant pipework that is run and connected on site. Site refrigerant work brings an F-Gas competence requirement.
A damaged float-valve washer that seals at daytime pressure but lets by under the higher night-time pressure, causing a cistern to overflow at off-peak times.
A tap that breaks the flow into a fine spray, cutting water use by about 20 per cent; rated at 0.04 l/s for sizing.
A point where the water table meets the surface and ground water flows out. Deep-fed springs are reliable; shallow ones dry up in summer.
The spring in a motorised valve that closes it when the electrical supply to the actuator is removed.
A branch connection made square into a stack, without a sweep in the direction of flow. It gives a stack less hydraulic capacity than a swept entry.
To let a newly filled system settle: float valves shut, pressure settles and the water reaches the temperature of its surroundings before inspection and testing.
The movement of air caused by warm, less dense air escaping upward through flues and openings, drawing cold air in at lower levels. It increases the air change rate.
The dry part of a discharge stack above the highest branch connection, carried to atmosphere. It may be reduced to 75 mm in one and two storey houses.
Filling a large system section by section, proving each leak-free before the next is opened.
A pass criterion applied at more than one point in time, as in Test B's 0.6 bar at 30 minutes and 0.8 bar at 150 minutes; each stage must be met on its own.
Water standing still in a cistern or pipe for long enough to warm, lose its disinfectant and grow bacteria. Cisterns are not oversized and dead legs are avoided so that water is held for as short a time as possible.
The maximum temperature a collector reaches with no heat being removed. Flat plates reach roughly 150 to 200 °C and evacuated tubes exceed 250 °C, and components are rated against this figure.
The government method for assessing the energy performance of dwellings. Its hot water demand formula is 25 times the number of occupants plus 36 litres a day at 52 degrees.
Fixed laboratory conditions used to quote heat pump performance, commonly written A7/W35 for air at 7 °C and water at 35 °C.
A spare cistern or compartment, required over 1,000 litres, that keeps the supply going while another is isolated for cleaning.
Heat lost from a store or from pipework to the surrounding air while nothing is being drawn off. It is limited by insulation and by keeping pipe runs short.
The number of times a manufacturer permits a heat generator to start in an hour. It is the figure behind a minimum system volume requirement.
The state of an installation when all the pipework, appliances and wiring are physically finished but the system has not yet been set to work, tested and adjusted.
The records of the pre-commissioning checks, required by BS EN 14336 before a system is set to work, showing the installation is complete, sound and safe.
The pressure produced by the height of water above a point, roughly 0.1 bar for every metre. It sets the minimum charge pressure for the vessel.
The vertical height the pump must raise the water, in a building the height from pump to the highest outlet or cistern.
The pressure in a pipe when no water is flowing. BS EN 806-3 limits it to 500 kPa (5 bar) at any draw-off point; above that a pressure-reducing valve is fitted.
Made or required by law. Statutory documents such as the Building Regulations and the Water Supply (Water Fittings) Regulations can be enforced in court; a voluntary standard cannot.
The customer's legal right to cancel a contract within a set period after signing, normally without penalty if confirmed in writing.
The protection Regulation 7(2) gives an owner or occupier who is prosecuted for a contravention: it is a defence to show that the work was done by an approved contractor and that the contractor certified it complied. Both halves are needed; approval without a certificate, or a certificate from someone who is not approved, fails.
An inspection or test the water undertaker is entitled to make. BS 8000-15 clause 4.1.1 requires prior notice of it.
A nuisance, including noise, that a local authority can act against under environmental protection law. It is separate from planning control.
A rule made under an Act of Parliament, so it is law and breaking it is an offence. The Water Supply (Water Fittings) Regulations 1999 and the Building Regulations are statutory; a British Standard is not.
Requirements that carry the force of law, such as the Building Regulations, the Water Supply (Water Fittings) Regulations and the Gas Safety (Installation and Use) Regulations. They cannot be overridden by a standard or an instruction.
The settled condition a system reaches once warm-up is over and temperatures have stopped changing. Commissioning readings are only valid when taken here.
An external combustion engine driven by heating and cooling a sealed working gas. It is the engine used in domestic micro-CHP units.
Using older stored material before newer, so that nothing exceeds its storage life before it is fitted.
An outlet fitted at the end of a gutter run, receiving water from one direction only.
A screw-down valve used to shut off the water supply to a building or a section of pipework. Underground stopvalves of 15 to 50 mm are made to BS 5433; those above ground to BS 1010.
The volume of hot water a vessel holds, quoted in litres. It is set from the likely consumption and the recovery rate together.
A heater that holds a quantity of heated water ready for use. The store is replenished with cold water as hot water is drawn off.
The cylinder or thermal store into which a solar thermal system puts its collected heat. Without a store there is nowhere for the energy to go, which rules out an instantaneous-only hot water supply.
The work the pump has done compressing the air in an accumulator, released as flow when a tap opens.
Any arrangement, such as a cable gland, clamp or a length of slack, that stops the weight or movement of a cable pulling on its terminations.
A mesh filter fitted upstream of a valve to keep grit off its seat.
The layering of water in a store by temperature, with the hottest water at the top. It lets the hottest water be drawn off first and is why the cold feed enters at the bottom.
The engineer responsible for the structure of a building, including loads, the frame and the foundations. Consulted on any question of load-bearing capacity.
A short unventilated stack, closed at the top, connecting ground floor appliances to a ventilated drain or ventilated discharge stack within set height limits.
An internal wall built of vertical timber or metal studs covered with plasterboard. It is hollow, so heavy appliances need a timber fixing board behind the board.
The compacted layer of stone prepared beneath a concrete slab so the slab is supported evenly and does not settle.
A smaller firm engaged by the main contractor to carry out a specific or specialised part of a contract, such as plumbing, heating or electrical work.
An outlet, hose end or tap spout that sits below the water level of the appliance or vessel it discharges into. Because it is under water it gives a path for back siphonage, so it needs a backflow device.
A sealed centrifugal pump hung below the water in a borehole that pushes the water up, so it has no suction-lift limit.
Replacing something hazardous with something less hazardous that does the same job, such as a press fitting instead of a soldered joint.
The two sides of a pump: suction (inlet), where water enters, and discharge (outlet), where it leaves under pressure. Gauges on both sides show whether the pump is doing its job — the suction reading falls and the discharge reading rises to the figure on the data plate.
The pressures on the inlet and outlet sides of a booster pump, recorded on the commissioning record.
The legal standard a risk assessment must meet: it must identify the significant risks, be proportionate to them, and set out what will be done about them.
The second Regulation 4 test: a fitting must be right for where and how it will be used, judged against temperature, corrosion, compatibility with other materials, ageing and fatigue, and permeability. An approved fitting can still fail this test, so only the installer, who knows the installation, can decide it.
Water held as a liquid above its normal boiling point because it is under pressure. If the pressure is lost it flashes instantly to steam.
The pipe carrying water at mains pressure from the water undertaker's main into and around the premises, up to the point where it feeds a cistern or an outlet. A common supply pipe is one shared by several separately occupied premises.
The maximum spacing between pipe clips or brackets, set in BS 8000-13 by pipe material, size and whether the run is vertical or near horizontal.
The condition where the water level in a sewer or manhole rises above the top of the pipe, usually in heavy rainfall, which interrupts the air flow in a connected stack.
A drain running full and under pressure, so that it can back up into the pipework connected to it.
A pump installed above the water, in a pump house or the building, that has to draw the water up by suction.
Water taken from streams, rivers, springs or lakes rather than from below ground. It varies with the weather and always needs filtration and disinfection.
Metal filings and cuttings left in pipework from cutting and deburring, removed by flushing.
A branch fitting whose entry is curved in the direction of flow, so discharge joins the main pipe smoothly instead of striking the opposite wall.
A branch connection curved in the direction of flow so the discharge joins smoothly, reducing blockage and suction. The opposite is a square or knuckle entry.
A tee fitting with a curved branch that lets water join the main flow smoothly, used where a secondary return joins the cold feed of an unvented cylinder.
The switched, fused connection unit through which a heating control system is supplied, fitted with a 3 A fuse.
A live conductor that is only energised when a control has called for heat, as distinct from the permanent live that is always energised.
What the system does that shows something is wrong, such as cold water at the taps or a dripping discharge pipe. The symptom is what you observe; the fault is what causes it.
A boiler containing the pump, expansion vessel and sealed system safety controls inside its own casing, so they do not have to be installed separately.
The calculated scheme for an installation, including heat loss, emitter sizes, flow temperatures, pipe sizes and controls. It is one of the three strands an installation is built from.
The person who determines the system's parameters, including expansion vessel size and charge pressure, so that all components work together.
The efficiency of the whole heating installation: the heat pump plus its auxiliaries, distribution pipework, controls and storage losses. It is what the customer actually pays for.
Everything recorded about a system since it was handed over — the commissioning record, logbook entries, previous call-outs, parts replaced and alterations. It is the fourth source of fault-finding information after the end user, the manufacturer’s data and flow charts.
The single stack system used in the United Kingdom, described in BS EN 12056-2. Each appliance has its own individually sized branch discharge pipe, running only partly full.
Durable labels fitted to a completed installation carrying the information the next person needs, such as the fluid type, fill pressure, isolation points and hot surface warnings.
An installation with low or no turnover, such as a school over the summer, where standing water is a contamination risk and disinfection is triggered.
A drawing of the system showing its circuits, components, valves and isolation points, so that anyone servicing it later can understand it without tracing pipes.
The total quantity of water in circulation. A heat pump needs enough volume in circuit to run steadily rather than cycling.
The pipe sizing tables of the simplified method, one per material, giving for each size the maximum loading units, the highest single appliance and the maximum section length. Table 3.2 is the copper table.
The traditional UK pipe sizing method in BS 8558 Annex C (formerly BS 6700 Annex D), used for buildings other than dwellings. For each numbered section the loading units are converted to a design flow, a size is assumed, head loss and velocity are read off the pipe chart, the equivalent length of fittings is added, and the residual head is checked; if it is too low the size goes up and the section is repeated.
Setting out a heat loss calculation in a table, one row per element and one table per room, so the figures can be checked and presented.
A cylinder in which an inner potable vessel sits inside an outer body of primary water, so heat transfers through the whole surface of the inner tank rather than through a coil.
The continuous waterproof layer, in sheet or liquid form, applied to the floor and lower walls of a wet room before the tiling goes on.
The air gap between the lowest part of a tap, combination fitting or fixed shower head and the spill-over level of the appliance below it. It protects against back siphonage only: type AUK2 over domestic basins and baths, type AUK3 over sinks and hospital basins.
The four headings of a manual handling assessment: what is being done, who is doing it, what is being moved and the conditions it is moved in.
The Scottish equivalent of the Approved Documents. Section 6 covers energy, including U-value standards for new and existing dwellings.
The design output for the project listing each loop with its length, flow rate and the number of turns from closed its regulating valve should be opened.
The manufacturer's own documentation for an appliance covering its operation, servicing and repair. BS EN 806-5 requires it to be available, retained and followed.
The manufacturer's help line, contacted when a pump set or accumulator still fails after the set-up procedure has been followed.
A three-way fitting used on a test connection, with a cock on each branch, so the pump and the manometer can both be connected and the air inlet closed.
A valve fitted directly on an unvented storage vessel that opens on excess temperature or pressure, so that the stored water cannot exceed 100 degrees. No valve may be fitted between it and the vessel.
The difference between two temperatures, written with the Greek letter delta. In heat loss it is the internal design temperature minus the external design temperature.
The fall in temperature between the flow and the return of a circulation, written Δt. On a secondary hot water circulation it may not exceed 10 K, because the flow leaves at 60 °C and the return must arrive at not less than 50 °C.
The state where the water and the surrounding air are at the same temperature. BS EN 806-4 allows 30 minutes to reach it where they differ by more than 10 K.
The difference between the temperature a heat pump takes heat from and the temperature it delivers heat at. The wider the lift, the lower the efficiency.
The safety device that shuts the appliance down if the water temperature exceeds the maximum operating temperature. Most boilers have one built in.
Holding water already at temperature in the distribution pipework, rather than reheating it, so that hot water is available at the outlet without running the tap.
A safety device fitted directly on an unvented storage vessel that opens between 90 and 95 degrees C to discharge hot water, ensuring the stored water cannot reach 100 degrees C.
The difference between the incoming cold water temperature and the temperature the water is heated to, in degrees Celsius. It appears in every heating calculation.
An in-line blending valve on the outlet of a store that can exceed 80 degrees C, holding the temperature sent to the distribution pipework to no more than 60 degrees C.
Isolating a system and taking it out of service until a faulty part can be replaced, so that it cannot be used in an unsafe condition in the meantime.
A filling loop is a temporary connection only. While it is coupled the verifiable double check valve protects the main; as soon as filling is finished the loop is uncoupled, so no connection remains. The named air gaps — AA, AB, AUK1, AUK2, AUK3 — are tap and cistern arrangements, and none of them describes a filling loop.
A supply of undertaker's water for non-domestic purposes that is metered, lasts no more than one month (or three months with the undertaker's written consent) and cannot return water through the meter, such as a contractor's standpipe. Regulation 2(2) puts it outside the Water Fittings Regulations.
The period the water undertaker has, from the day a Regulation 5 notice is given, to respond. If it has not consented, refused or attached conditions by then, Regulation 5(5) deems consent granted unconditionally and work may start.
A formal priced offer to carry out a described contract, submitted in competition with other contractors. It is supported by the calculation sheet, scale drawings, the specification and a bill of quantities so the price can be checked.
An agreement to carry out work of a defined kind over a period, usually paid against a schedule of rates rather than a single fixed price.
The tap, shower or valve at the end of a pipe where water is drawn off and flow is measured.
The place where a discharge pipe ends and releases water, outside the building and where the discharge is visible but cannot scald anyone.
The Water Regulations plastics test: pump 30 minutes at test pressure, reduce to one third, and the pressure must not fall below one third over 90 minutes.
The Water Regulations plastics test: pump 30 minutes at test pressure, then a drop of under 0.6 bar in the next 30 minutes and under 0.8 bar over 150 minutes, each stage met on its own.
The shorthand attached to a quoted efficiency figure, giving the source and output temperatures. A7/W35 is air in at 7 °C, water out at 35 °C; B0/W45 is brine in at 0 °C, water out at 45 °C.
The small connection point built into a test plug or cap to which the test hose is attached.
A mechanical or inflatable stopper fitted into the open end of a pipe to seal it for testing. An inflatable one is often called a drain bag or test bag.
A small tapping on a backflow device to which a gauge can be connected so the device can be tested in place. A device with test points is verifiable; a type EA check valve has one, a type EC double check valve two and an RPZ valve three.
The pressure a system is tested at: not less than 1.5 times the maximum pressure it is designed to be subjected to in operation.
The document stating the test pressure used and that no leaks were found, required by BS EN 1264-4 before the screed is laid.
The electrically operated head on the return bar of a manifold that opens or closes one circuit in response to that room's thermostat.
How readily a material conducts heat, in watts per metre kelvin. It is a property of the material regardless of how thick it is.
A protective device that switches a motor off when it overheats, for example when the grinding blades jam. It must be accessible so it can be reset after the cause is cleared.
Disinfecting a hot water system with heat instead of chemicals, by raising the stored water so outlets stay at or above 65 degrees C and flushing every outlet at that temperature.
The increase in length of a pipe as it heats up. Plastic heating pipe grows about 10 mm per metre at 60 °C where it is free to move.
The delay between a heating system starting and the room reaching temperature, caused by the mass of the floor that has to be warmed first.
The heat stored in the floor structure. It steadies room temperature and evens out the heat output, but it also makes the system slow to respond.
The resistance of a layer of material to heat flow, found by dividing its thickness in metres by its k-value. R-values of the layers are added together to find a U-value.
The rapid cooling or heating of a component, such as a boiler heat exchanger, which can lead to failure of the material.
A test on a thermostatic mixing valve in which the cold supply is isolated and the mixed water monitored. The outlet flow should stop quickly, proving the valve fails safe.
A vessel storing primary water heated by a boiler, through which mains cold water passes in heat exchangers to be heated on demand. Also called a water jacketed tube heater.
The rate of heat transfer through an element of a building, in watts per square metre kelvin. The lower the U-value, the better the element keeps heat in.
A valve that mixes hot and cold to a set safe temperature before the tap, so a sensor tap cannot scald.
A mixing valve that holds a set outlet temperature. BS 8558 notes it may not need balanced hot and cold pressures; the manufacturer's instructions decide.
A self-acting valve that senses the air around it and throttles the water into its own radiator. It cannot switch the boiler off, so it may never be the sole control.
Natural circulation caused by density difference, hot fluid rising and cool fluid falling. It requires the store to be above the collector.
A valve that blends cooler return water into the flow to control the temperature of a circuit, for example an underfloor circuit. It does not select between circuits.
The angle of a collector from the horizontal. A fixed collector uses a compromise angle, about 35° in the UK.
A length of timber fixed between or across the studs of a partition wall so that a wall-hung basin or bracket has something solid to screw into. Needed on plasterboard partitions; solid brick, blockwork and concrete take fixings directly.
A clock-controlled switch that opens a solenoid valve on a urinal supply only during the hours the building is occupied.
The weekly record each employee completes of hours worked and jobs carried out, used to calculate wages and to inform future estimates.
The panel, usually in the corner of a drawing, giving the project, the drawing number, the date, the revision and the scale. Read the scale from it before measuring anything off the drawing.
The certification class for thermostatic mixing valves in domestic installations, tested against BS EN 1111 and BS EN 1287.
The certification class for thermostatic mixing valves in healthcare and commercial installations, tested against NHS specification D08.
An earthing system in which the distributor combines neutral and earth in one conductor up to the cut-out, and the installation takes its earth from that combined conductor. Also called protective multiple earthing.
A measure of the thermal resistance of a floor covering. Coverings over underfloor heating should be below 1 TOG and never above 1.5, covering and underlay together (BS EN 1264).
A short informal meeting held on site, usually before the day's work, to deal with one matter of health and safety or safe working practice.
The floor area within the insulated envelope of the dwelling, including internal cupboards and stairwells. It is the figure compared with 150 m² for zoning.
The design flow rate where continuous flows or pumped discharges are also connected. These are added to Qww without any reduction.
An electric heating cable run along a pipe, under its insulation, to keep the water inside at a set temperature. It removes the need for a secondary return.
The ability to trace a recorded result back to the person, date and equipment that produced it, so a later query can be answered.
The person who runs one trade's work on a site, allocating duties to the operatives under their direct control and co-ordinating with other trades.
The older UK loading unit scale kept in BS 8558 Annex C for buildings other than dwellings: WC 2, basin 1.5 to 3, bath 10, shower 3, sink 3. The numbers differ from the BS EN 806-3 scale, so the two are never mixed in one calculation.
The last dribble of water at the end of an appliance discharge, which runs back into the trap and refills the seal. It is why baths and sinks siphon less readily than basins.
A pipe fitting, or part of an appliance, that holds liquid to stop foul air passing from the drainage system into the building.
The depth of water held in a trap, measured in millimetres. Seals are 75 mm or 50 mm depending on the appliance, and at least 25 mm must remain after use.
A drainage fitting with a water seal. A discharge pipe terminating in one ends below the fixed grating and above the water seal.
The direction a reading moves across successive service visits. A trend can show a fault developing long before the system fails.
A urinal control that lets the cistern fill only very slowly if no movement is detected for a set time.
A trap formed from a bend of tube of the same bore as the waste pipe, so there is no reduction in flow area. An S trap has a vertical outlet, a P trap a near-horizontal one.
An open funnel-shaped fitting that receives a discharge through a visible air gap and carries it to drain. The relief port of an RPZ valve or type CA disconnector discharges through a tundish giving a type AA air gap at least 300 mm above the floor.
A measure of the cloudiness of water, in nephelometric turbidity units (NTU). Treated greywater for most uses must be below 10 NTU.
Flat sheathed cable containing an insulated line core, an insulated neutral core and a bare circuit protective conductor between them. The standard cable for domestic fixed wiring.
A cylinder with two heat exchanger coils: a lower one for the solar circuit and an upper one for the auxiliary heat source.
A shower pump with two impellers that boosts the hot and cold supplies separately on the inlet side of the mixer.
A pump fitted before the mixing valve with one motor driving two impellers, boosting the hot and cold supplies separately.
A storage vessel with two separate primary coils, one low and one high, so that two heat sources can serve different parts of the store.
A radiator valve that takes both the flow and the return into a single radiator tapping through a concentric spigot, used with microbore legs.
A buffer connected in series with the circuit, so all the flow passes through it and the emitters receive the generator's flow temperature.
A heating layout with a separate flow main and return main. Every emitter draws from the flow and discharges into the return, so all emitters receive water at nearly the same temperature.
A motorised valve that opens or closes one circuit. It is driven open by a motor and closed by a return spring, and carries an auxiliary switch.
An unrestricted air gap between a discharge pipe and the water it discharges into, so nothing can flow back.
An air gap with weir overflow: as type AA, but measured to the critical level of a rectangular weir overflow cut in the wall of a cistern that can be closed with a lid and screened against insects. The gap is twice the inlet diameter. Rated category 5 both ways, and the usual mains back-up arrangement for a rainwater or greywater cistern.
An air gap with injector: a horizontal jet, sometimes called a jump jet, throws water across a gap of 20 mm or twice the inlet diameter into the appliance. Rated category 5 both ways; found inside commercial washing and dishwashing machines and catering equipment.
An air gap with a circular overflow, rated to fluid category 4. Used with type AB on large storage cisterns where the critical level of a small overflow cannot be predicted. Type AC, a submerged feed with air inlet, is rated category 3.
The air gap between a cistern inlet and the overflow level, at least twice the inlet diameter, that prevents backflow into the inlet.
An air gap with interposed cistern: a cistern with a type AG gap and overflow stands between the supply and a receiving vessel whose spill-over level is at least 300 mm below the overflow pipe and 15 mm below the bottom of the cistern. Rated category 3 for back pressure and 5 for back siphonage. A conventional WC suite is the everyday example and needs no further backflow device.
The tap gap over a domestic wash basin, bath, shower tray or over-rim bidet, where the risk is fluid category 2 or 3. Back siphonage only, to category 3. Minimum gap by tap size: 20 mm up to G half, 25 mm up to G three-quarters, 70 mm above G three-quarters.
The tap gap over any sink, domestic or not, and over any appliance in premises needing a higher level of protection such as a hospital basin, where the risk is fluid category 4 or 5. Not less than 20 mm or twice the bore of the tap inlet, whichever is greater. Back siphonage only, to category 5.
A backflow preventer with non-verifiable reduced pressure zones, rated for fluid category 3. It is tested by closing the upstream stopvalve and checking that nothing discharges from its port, and is replaced if it fails.
A backflow prevention device with an integral tundish, allowing a permanent connection to a fluid category 3 system such as a domestic heating primary.
A non-verifiable disconnector: a small RPZ without test points, with two check valves and a chamber between them that opens to atmosphere through a tundish when upstream pressure is lost. The pressure zones differ by not more than 10 per cent. Rated category 3 both ways; used for a permanent connection between a sealed heating system and the supply pipe.
A pipe interrupter with atmospheric vent and moving element: water leaves through side holes covered by a rubber membrane, and when supply pressure is lost the membrane closes the holes and vents open to air. Back siphonage only, to fluid category 4. Used at the hose union tap or 300 mm above a porous irrigation hose in a house garden, fitted vertically with no valve downstream.
A pipe interrupter with permanent atmospheric vent: a brass fitting with no moving parts whose air holes are always open, so if back siphonage starts air is drawn in and the siphon breaks. Back siphonage only, to fluid category 5. Fitted vertically, discharging downwards, with no valve or restrictor downstream, at least 300 mm above the spill-over level of a WC pan or urinal served by a pressure flushing valve.
A small device that screws onto the outlet of a hose union bib tap; a spring and membrane close against backflow and admit air to the hose when pressure drops. Rated category 2 for back pressure and 3 for back siphonage. Permitted only, fitted continuously, on an existing unprotected hose union tap in a house.
A diverter with automatic return built into modern bath/shower mixers that provides backflow protection for the hose.
A hose union bib tap with two single check valves built in, one at the inlet and one at the outlet, and a test point on the body. Rated category 3 both ways. Because mechanical devices belong inside the building it is permitted only as a replacement for an existing unprotected outside tap; a new tap gets a double check valve inside.
The classification used by Table NG.1 to set the number of appliances discharged: domestic, commercial or public, or congested.
The rate at which heat passes through a building element, in watts per square metre per kelvin. A lower number means better insulation; a ground floor target is 0.25 W/m²K.
A hand-held instrument that measures distance by timing a pulse of sound reflected off a wall. Quick to use, but any obstruction between it and the wall gives a false reading.
The embrittling and cracking of cable sheathing caused by sunlight. Any part of a cable run outdoors must be UV resistant or protected from sunlight.
Disinfection by a 254 nm mercury lamp in a quartz sleeve that changes the cellular structure of micro-organisms so they cannot reproduce. Needs clear water and leaves no residual.
The supply pipe serving the lower floors of a tall building straight from the main, with no pump.
Hot and cold supplies to a mixer arriving at different pressures, for example mains cold and cistern-fed hot. The higher pressure can push water across into the lower pressure supply, so BS 8558 asks for comparable pressures and single check valves on each feed.
An arrangement in which the hot and cold supplies to a mixer are at different pressures. Mixers and thermostatic mixing valves may not blend correctly, and there is a risk of backflow or scalding.
A blending valve and dedicated pump that mix return water into the underfloor flow to hold it at the lower temperature underfloor circuits need, while radiators run hotter from the same generator.
A wet heating system in which pipe circuits embedded in or under the floor make the floor itself the heat emitter, running at low water temperature.
A riser too small to carry the design total flow. It cannot be balanced out and is referred to the designer.
Selecting a heat source with less output than the building's design heat loss. An undersized heat pump runs continuously in cold weather, still fails to hold temperature, and leans on expensive back-up heat.
The temperature of the ground before any heat is drawn from it. Below the zone of seasonal variation it sits close to the annual average air temperature for the site.
One of the five harms: water used for its proper purpose but in far greater quantity than the job needs, such as a urinal cistern that goes on flushing all weekend in an empty building.
A proprietary unvented hot water storage system supplied with all its components already fitted at the factory.
A control strategy that lowers the target room temperature by about 4 K during unoccupied periods instead of switching the heating off, so warm-up from the next occupied period is faster.
Work carried out in response to a failure or an emergency, where the system has already stopped performing.
A fixed electrical connection point with a fuse and no switch, used so an appliance such as a macerator cannot be casually switched off.
A hot water storage cylinder fed directly from the supply pipe at mains pressure, with no vent pipe or cistern. Its expanded water would back into the supply, so its inlet group carries a single check valve.
A hot water storage vessel fed directly at mains pressure with no open vent or feed cistern. Its safety devices discharge through a D2 pipe to a safe, visible place outside.
A stored hot water system with no open vent pipe, fed directly from the cold water main so that the stored water is above atmospheric pressure.
The vertical pipe rising from a drinking water header on which the automatic air inlet valve is fitted.
Towards the water undertaker's main, the direction water comes from. Downstream is the opposite direction, away from the main and towards the outlets; a backflow device protects everything upstream of it from whatever is downstream.
The end of a branch discharge pipe furthest from the stack. Discharges from appliances here pass every other junction, giving the worst pressure conditions.
A continuous urinal surface without individual bowls. It is counted for flushing purposes as one position for each 700 mm of width.
The portion of a cylinder contents that can be drawn off at a useful temperature before the delivery cools. Typically 70 to 80 per cent of net volume in a well-designed vessel.
In Regulation 3, anyone who uses a water fitting on an undertaker's supply, including the owner and occupier of the premises. The user must not use a fitting in a way likely to cause one of the five harms, must not use a damaged, worn or faulty fitting, and is liable to prosecution where the installer cannot be traced.
Ultraviolet water treatment fitted to deal with contamination in an incoming supply such as a private supply; it does not clean an already contaminated installation.
An ultraviolet lamp in a tube that disinfects water passing through it, used in rainwater and greywater treatment. Treatment does not change the fluid category: treated rainwater or greywater is still category 5.
A valve that admits air when the pressure inside a vessel falls below atmospheric, preventing the vessel from collapsing inwards.
The fixed date, usually monthly, on which the work completed and materials on site are measured so that an application for payment can be made.
A diagram fixed in the building identifying every valve, an alternative to individual valve labels under BS EN 806-4 clause 4.9.4.
Operating a stop valve at least once a year so it does not seize (BS 8558 clause 6.2.2.3).
The label BS EN 806-4 clause 4.9.4 requires on each valve so that what it isolates can be identified.
A contract where agreed rates are applied to the quantity of work actually carried out, so the final sum is not known at the outset.
An inlet valve whose shut-off level can be adjusted so the stored volume is reduced when occupancy is low.
A change to the work agreed after the quotation was accepted. It should be recorded in writing, with its price, before it is carried out.
A clause in a construction contract that allows the works to be changed after the contract has been signed, and sets out how such changes are valued.
The document that records an agreement made with a client to alter the work specified in a building contract, stating the change in cost and in time.
Value Added Tax, added to the price at the rate in force where the business is registered for it. It is shown separately from the price of the work.
The speed at which water travels along a pipe, in metres per second. Flushing needs at least 2 m/s to lift and carry debris out of the system.
An arrangement in which individual branch discharge pipes are given their own ventilating pipes, used where a branch is too long, too steep or has too many bends to run unventilated.
A layout in which each appliance has its own branch ventilating pipe, used where appliances are in ranges or widely dispersed from the stack. Previously the ventilated or modified single stack system.
The through-ventilated space under a suspended ground floor. Air moving through it disrupts a reflective foil system, so foil must not be used over one.
A vertical dry pipe that carries ventilating air. It either collects branch ventilating pipes or cross-connects to a discharge stack, and terminates at atmosphere or into the stack vent.
Heat lost as warm air leaves the room and cold air replaces it, whether by infiltration or by mechanical ventilation. Calculated from room volume, air change rate, temperature difference and the 0.33 factor.
Releasing air from a system as it fills, by opening the highest draw-off points so that the air is pushed out ahead of the water.
A deliberate narrowing in a waterway that speeds the flow and lowers the pressure, used in a gas instantaneous heater to operate the gas valve.
Talking the fault through with the end user, face to face or by telephone, then asking follow-up questions to narrow the cause down. It is the recognised way of gathering the immediate history of a fault.
Asking the customer in conversation whether the installation meets their expectations, the right way to obtain feedback on a new system.
Describes a backflow device that has test points, so its check valves can be tested in place without removing it. A non-verifiable device has no test points and can only be checked by taking it out.
A single (EA) or double (EC) check valve fitted with a test point, so that its operation can be proved in place. Under BS EN 806-5 it is inspected and maintained once a year.
Ground loop pipework installed in one or more drilled boreholes. Used where land area is limited, it reaches deeper and more stable ground at a significantly higher drilling cost.
The rise in a pumped discharge pipe from a macerator or lifter. One lift is recommended, at the start of the run, before the pipe falls to the stack.
A centrifugal pump with several impellers stacked in a vertical column, each adding pressure, used on most booster sets.
A plastics pipe material such as PE, PP, PEX, PA or PB that both stretches and creeps under pressure, so its pressure reading falls over time even without a leak.
Water that can be seen escaping from the installation during a test. Any visible leakage fails the test regardless of what the gauge reads.
A toilet on the entrance level of a dwelling planned with enough space for most people to use it, including a wheelchair user, so the activity space in front of the pan is deeper than the standard.
The first commissioning activity: a walk of the whole installation with the pipes empty, comparing what has been built with the specification, drawings and manufacturers' instructions.
BS 7671's grouping of circuits by voltage. Band I covers extra-low voltage such as sensor and signalling circuits; Band II covers normal low voltage mains circuits.
A two-pole instrument used to establish the presence or absence of voltage. For safe isolation it must be made and maintained in accordance with HSE guidance GS38.
A two-port buffer vessel fitted in series on the return purely to add system volume. One pump still serves both sides, so it does not separate the circuits.
A fitting that cannot take the test pressure, removed and replaced with temporary pipe for the test.
A fully pumped system controlled by a three-port diverter valve, which serves either the hot water or the heating. It gives hot water priority.
A long test lead used to reach from the origin of a circuit to a distant point, so a continuity measurement can be made without a second person.
A durable tag or notice fixed at the point of isolation stating that work is in progress, who applied the isolation and what is being worked on.
An overflow pipe fitted to give warning of an impending overflow, discharging in a conspicuous position. On a cistern up to 1,000 litres it is the only overflow.
The indelible notice Approved Document G requires on an unvented hot water storage unit or package, visible after installation. It tells the user not to adjust any component and to switch the heater off and contact the installer if hot water flows from the discharge pipe.
The manufacturer's guarantee on a component, which an unauthorised repair can void; a defective component goes back to the manufacturer and supplier.
A WC pan cleared by the weight and momentum of the flush water washing the contents through the trap.
A pan emptied by the force of the flush water alone, with no siphon formed in the trapway.
A drain pipe from the lowest point of a large cistern, discharging over a type AA air gap, used to empty it for cleaning.
Material paid for but not installed, whether through offcuts, damage, over-ordering or loss. It is measured by reconciling material issued against work installed.
A percentage added to the measured materials to cover offcuts, breakages and material that is paid for but not installed.
One of the five harms the Water Fittings Regulations exist to prevent: water escaping from the system to no purpose, such as a dripping overflow or a leaking joint.
A motorised grinder fitted under a kitchen sink that reduces food waste to a paste which water carries into the drainage system.
The used water discharged from basins, baths, showers, sinks, washing machines and dishwashers. It carries no human waste.
The expected flow of waste water in part or all of a drainage system where only domestic sanitary appliances are connected, calculated as K times the square root of the sum of the discharge units.
A self-contained tank, pump and control unit that lifts waste water from below sewer level and discharges it into the drainage system through a backflow loop.
A packaged tank, pump and control unit that lifts waste water from below sewer level into the gravity drainage system. Covered by BS EN 12056-4.
A unit that collects wastewater in a chamber and pumps it up to a gravity drain. Lifting plants are covered by BS EN 12056-4.
A packaged tank, pump and controls that lifts wastewater to a drain above it. Faecal types are covered by prEN 12050-1 and must be vented above roof level.
The Act that updated water industry regulation in England and Wales: how water companies and licensed suppliers are regulated, charged and enforced. It is not where the plumbing rules come from. The Water Supply (Water Fittings) Regulations 1999 are made under section 74 of the Water Industry Act 1991 and came into force on 1 July 1999, four years before this Act existed.
The rules each water company used to make for itself under the Water Act 1945 to control fittings on its supply. Regulation 14 of the Water Fittings Regulations revoked them in England and Wales in 1999; Scotland still uses byelaws, the Water Supply (Water Fittings) (Scotland) Byelaws 2014.
A system that replaces wholesome water with water from another source for uses that do not need drinking quality, such as rainwater harvesting or greywater re-use.
The calculation that shows a new dwelling's fittings will use no more than 125 litres of water per person per day, required by Part G. It must be sent to the building control body within 5 days of completion (Regulation 20E), and the completion certificate is unlikely to be issued without it.
The government calculation method that adds up the water use of the fittings specified for a new dwelling to show it meets the 125 litres per person per day limit. The result is notified to building control.
In the Regulations, any pipe, tap, valve, cistern, cylinder, appliance or other apparatus through which water from an undertaker passes or in which it is stored. The word covers far more than pipe joints: a bath, a washing machine and a boiler filling loop are all water fittings.
A way of expressing a small pressure as the height of a column of water it will support, written mm wg. 38 mm water gauge is the pressure that lifts water 38 mm in a manometer.
A device fitted to the inlet of an instantaneous water heater to hold the flow through it steady, so the outlet temperature stays constant.
A pressure wave set up when moving water is stopped suddenly by a quick-closing valve, giving a bang and vibration; it can reach twice the working pressure.
The Act of Parliament that governs the public water supply and sewerage industry in England and Wales. Section 74 gives the power under which the Water Supply (Water Fittings) Regulations 1999 were made.
The building's record of water-hygiene documents, into which the disinfection certificate and data sheets go at occupancy (PD 855468 clause 14).
The body that publishes the Water Regulations Guide and the Water Fittings and Materials Directory, and operates the approval arrangements showing that a fitting complies with the Water Regulations.
The WRAS publication that prints the Water Supply (Water Fittings) Regulations 1999 alongside the official guidance on meeting each requirement, including the backflow device tables. It is the installer's working reference, because the duty to comply falls on whoever installs the fitting.
Taking stored drinking water for analysis at intervals not exceeding six months except in single dwellings (BS 8558 clause 6.1.4.1).
An appliance that removes calcium and magnesium hardness from the supply, usually by ion exchange: the water passes through resin beads that swap the hardness for sodium, and the resin is regenerated with salt. Because it swaps one ion for another it barely changes the pH, so the direct check on it is a hardness test on samples taken before and after the unit.
The law governing the design, installation and use of water fittings in premises supplied by a water undertaker in England and Wales, made under section 74 of the Water Industry Act 1991 and in force from 1 July 1999. They replaced the water byelaws, are enforced by the water undertaker, and exist to prevent waste, misuse, undue consumption, contamination and erroneous measurement of water. Scotland has the equivalent Water Byelaws 2014 and Northern Ireland the 2009 Regulations.
A test in which pipework is plugged and filled with water to check for leaks. On sanitary pipework it applies only below the lowest appliance and within a 6 m static head.
The record of a soundness test, giving the date, the test pressure, the duration and the result, signed by the operative and where required witnessed.
Any device that changes the quality of the water, such as a softener, filter or reverse osmosis unit. One that discharges waste water, or needs water to regenerate or clean itself, is notifiable under item 4(f) of Regulation 5.
The company appointed under the Water Industry Act 1991 to supply water in an area, and which owns the mains. It enforces the Water Supply (Water Fittings) Regulations 1999 in its area, must be notified of certain work before it starts, and decides whether to consent to it.
The alternative flush in BS EN 806-4 clause 6.2.3 using a pulsed water and air mixture at a minimum of 0.5 m/s in sections of no more than 100 m.
A trap seal formed by a membrane or valve rather than by standing water. Approved Document H allows a seal of 25 mm of water or equivalent, which covers these devices.
A vessel whose diaphragm or bladder has ruptured, so water has filled the gas side and there is no compressible cushion left. It cannot take up expansion and the expansion valve discharges on every reheat.
Loss of a trap seal caused by wind-driven pressure fluctuations at an exposed vent terminal, which set the trap water rocking until it spills over the weir.
A unit behind or beside a WC that grinds the discharge and pumps it away through small-bore pipework, used where gravity drainage is not available.
A control function that maintains internal temperatures by varying the flow temperature from the heat generator relative to the measured outside air temperature.
A joint that lets a small amount of water past under pressure, remade after the fill while the pressure is low.
A cup or jug with a slot cut in its side: held under a running outlet, the height the water reaches against the slot reads the flow rate on a scale. It checks flow rate, not pressure; if the flow spills over the top the reading is false and a flow meter is used instead.
A rectangular slot cut in the wall of a cistern, screened against insects, that lets water spill out at a known level. It is sized for the inlet flow and gives the critical level for a type AB air gap.
The toilets, washing facilities, drinking water, rest and changing arrangements that must be available to workers, and whose location and access are stated in a method statement.
A dug shaft at least 1 m in diameter reaching down to ground water.
A fully waterproofed room with a walk-in shower, where the room itself acts as the enclosure and the floor falls to a gully.
A hand-operated radiator valve with a turning head, giving simple on and off control at the emitter.
A backflow device at the point of entry, where the supply pipe enters the premises, so the water undertaker's main is protected from everything on the site. Usually a type BA RPZ valve; required under Schedule 2 paragraph 15(4) between separately occupied premises or when the undertaker gives notice, and secondary to point of use protection.
Designing a dwelling to a single internal temperature throughout instead of room by room. It reduces calculation but tends to oversize the system.
Water that meets the drinking water quality standards in the water supply regulations and is therefore fit to drink, cook with and wash in; the European standards call it potable water. Mains water from an undertaker is wholesome; private supply water counts as wholesome only if it meets the Private Water Supplies Regulations; rainwater and greywater never do.
The Water Industry Approved Plumber Scheme, the first scheme set up by the water companies through which a plumber can become an approved contractor under the Water Fittings Regulations.
The negative pressure created by wind passing over a roof and array, which tries to lift the collectors and their fixings. It usually governs the fixing design.
The junction box in which the supply, controls, valves, boiler and pump are interconnected, so the system wiring can be made and traced in one place.
The combination of cable, its method of installation and its support, taken together. Single cores in conduit and twin-and-cpc clipped to a wall are both wiring systems.
A test whose pass is watched and signed for by a second person, so the record carries a signature as well as a figure.
Work in any place where a person could be injured by falling from it, including places at or below ground level. There is no minimum height.
Regulations applying to all work at height where there is a risk of a fall liable to cause injury. They require the work to be avoided where possible, and otherwise planned, organised and carried out by competent people with inspected equipment.
A document that plans work activity against the time frame of a job or contract, so that the work is completed to the agreed schedule and progress can be measured against it.
The agreed set of checks and records a company or site uses to control the quality of work, including stage inspections, test records and snagging lists.
A system that prevents a person from reaching a position from which they could fall, as opposed to arresting a fall after it has begun.
The dimensioned, scaled plans, elevations and details issued with the specification so the contractor can price the job and build from them.
The pressure at which an appliance is designed to operate. A thermostatic shower, unvented cylinder or booster set has a minimum working pressure and flow rate in its data sheet, and the cold water design must deliver them at the appliance.
The standard of work Regulation 4(5) demands. Regulation 4(6) defines it as work that conforms to an appropriate British Standard, a specification approved by the regulator, or a method approved by the water undertaker, so it refers to documents, not to neatness.
The standard to which an installation is actually built on site. For above ground drainage it is set out in BS 8000-13, which Approved Document H paragraph 1.37 refers to.
The Water Regulations Advisory Scheme, the industry body that publishes the Water Regulations Guide and guidance notes, approves fittings and materials, and accredits the testers who commission and test RPZ valves.
The WRAS Information and Guidance Note that sets the colour code for reclaimed water pipes (green, black, green), cited by BS 8525-1 and Approved Document G.
The Water Regulations Advisory Scheme (WRAS) is the body the water suppliers set up to publish guidance on the Water Fittings Regulations and to test and list fittings that meet them. Its Guide explains how to comply but is not the law, and a WRAS listing is evidence of appropriate quality, not the statutory test.
A fully pumped system controlled by a single three-port mid-position valve, which can serve the heating, the hot water, or both at once.
The proportion of rain falling on a collection surface that reaches storage, typically 0.7 to 0.8 on a standard pitched roof.
The efficiency of a collector when the absorber and ambient air are at the same temperature, so there is no driving force for heat loss. Also called optical efficiency, it is the intercept of the efficiency curve.
An area of a dwelling heated by its own circuit, with its own valve, temperature control and time control, so it can be run independently of the rest.
A backflow device on the pipe serving one part of a site, such as a floor, a process area or each separately occupied premises fed from a common supply pipe, so that a risk in that zone cannot reach the rest of the building. It is secondary protection, additional to the point of use devices within the zone.
An isolating valve that shuts off one area or floor of a building’s system so that work can be done there while the rest stays in service.
Dividing a dwelling's heating into separately controlled circuits, each with its own valve, time control and temperature control.
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