If your pipes bang loudly when the washing machine fills, or when you turn a tap off quickly, you are hearing water hammer. It is a hydraulic shockwave, and it does more damage than most people realise.
What causes it
Modern washing machines and dishwashers use fast-acting solenoid valves that shut the water off almost instantly. All the moving water behind that valve has momentum, and when it stops dead the energy has nowhere to go, so it sends a pressure wave crashing back through your pipework.
If the pipes are not clipped tightly to joists or walls they physically move and strike the structure. That is the bang you hear.
What damage water hammer causes
This is not only noise. Repeated shockwaves will:
- Loosen compression fittings until they weep
- Weaken soldered joints over time
- Cause hidden leaks under floorboards and inside wall cavities
- Shorten the life of appliance inlet valves
The leak that appears three years later under a kitchen floor often started as a banging pipe that everyone got used to.
Fix one: check the pipe clips
Look at the visible pipework, usually under the kitchen sink or near the boiler. Push gently on the pipes. If they move easily and nothing is holding them, that movement is your noise.
Adding clips to secure the run tightly to the wall or joists can resolve minor rattling. It costs very little and it is a sensible first thing to try.
Fix two: fit a shock arrestor
If the noise is a single sharp bang rather than a rattle, clipping will not cure it, because the problem is the pressure wave itself.
The proper fix is a shock arrestor, sometimes called a mini expansion vessel, fitted to the supply pipework near the appliance. Inside is a pressurised air bladder. When the valve slams shut the bladder compresses and absorbs the shockwave instead of letting it travel back through the house.
It is a straightforward job for a plumber and it permanently cures appliance water hammer.
Getting it sorted
We fit shock arrestors and secure loose pipework for homeowners across Crawley, Horsham and the surrounding areas regularly. If your pipes bang every time you run a wash, it is worth dealing with before it becomes a leak.
Frequently asked
Is water hammer actually damaging my pipes?
Yes. Each shockwave puts mechanical stress on the pipework. Over time that loosens compression fittings, weakens soldered joints and can cause hidden leaks under floors or inside walls. The noise is a warning rather than just a nuisance.
Can I fix banging pipes myself?
Sometimes. If the pipes are visibly loose under a sink or near the boiler, adding pipe clips to secure them properly can stop minor rattling. If the noise is a sharp bang rather than a rattle, that is a pressure shockwave and clipping alone will not cure it.
What is a shock arrestor?
A small sealed vessel containing a pressurised air bladder, fitted to the supply pipework. When a valve slams shut the bladder compresses and absorbs the energy instead of letting it travel through your pipes. It is the definitive fix for appliance water hammer.