Noise Faults: Three Noises, Three Causes, Three Corrections

Every noise in a cold water system tells you where the fault is. The trick is not listening harder — it is noticing exactly when the noise happens.

The three noises

Noise is one of the most common complaints in a cold water system, and each noise points to a specific fault. Learn them as three pairs of cause and correction.

Humming or squealing when a tap is opened

Cause: a worn or split tap washer vibrating in the flow.

Correction: renew the tap washer.

A washer that has hardened or split no longer sits still. The water rushing past it makes it flutter, and the flutter is the noise.

Loud hum in the pipework

Cause: a worn or split washer in the float operated valve, vibrating as the cistern fills.

Correction: renew the FOV washer.

Exactly the same mechanism as the tap, in a different place. The difference is that this one happens on its own, without anybody touching a tap.

Loud or violent banging in the system

Cause: loose or incorrectly supported pipework moving and striking the structure when the flow stops suddenly.

Correction: identify the loose pipework and refix it.

Telling them apart

The useful question is when the noise happens. That alone separates all three.

• Only while a tap is running → the tap washer.
• Only while a cistern is filling, and it stops when the cistern is full → the float valve washer.
• A bang as the water stops → loose pipework.

So on the phone, before you have seen anything, three questions get you most of the way: does it happen when you run a tap, does it happen after flushing the WC, or does it happen the moment something turns off?

Water hammer

The banging has a proper name: water hammer.

Here is what is actually happening. Water in a pipe has weight and it is moving. When a valve closes, that moving column of water is stopped suddenly, and all its momentum has to go somewhere. It becomes a pressure shock that travels back along the pipe.

That shock makes the pipe jump. If the pipe is properly clipped, it cannot move and you hear nothing. If it is loose, it moves and hits the joist, and the bang travels through the structure of the house — which is why the noise often seems to come from a completely different room.

Why it has got more common

Worth knowing, because customers notice it after a new appliance goes in.

Quarter turn ceramic taps and washing machine valves make water hammer more likely, because they close so quickly. A traditional tap takes several turns to close, so the water slows down gradually. A quarter turn tap or a solenoid valve in a washing machine shuts in a fraction of a second, and the faster the stop, the bigger the shock.

Proper clipping is the answer. The pipework was probably always underclipped; the new appliance just revealed it.