Water hammer is a pressure wave created when moving water stops or changes direction suddenly. The resulting bang or vibration can loosen fittings, stress valves and disturb pipe supports.
Before you worry
A single tick from thermal expansion is different from a sharp bang when a tap, toilet valve or appliance closes. Identifying the trigger is an important first step.
How to recognise the problem
- Sharp banging when taps close.
- Pipes shake when washing machines or dishwashers stop filling.
- Noise occurs when toilet cistern valves shut.
- Repeated vibration near pressure valves.
- Leaks develop at joints after ongoing hammer.
Common causes
- Excessive water pressure.
- Fast-closing solenoid or toilet valves.
- Loose or poorly supported pipes.
- Missing or failed arrestors.
- Air chambers that no longer function.
- Pump start-stop behaviour.
What you can safely check yourself
- Identify which fixture triggers the noise.
- Note whether it occurs on hot, cold or both systems.
- Check for visible loose pipe clips where safely accessible.
- Arrange pressure measurement.
What you should never do
- Do not wedge pipes tightly against structural surfaces.
- Do not keep increasing pressure.
- Do not ignore new leaks after severe banging.
- Do not install random arrestors without locating the pressure wave source.
When to call a plumber
Call a plumber when hammer is strong, frequent, associated with high pressure or causing movement and leaks.
How professionals solve it
The plumber measures pressure, observes the triggering valve, checks pipe support and system layout, and may regulate pressure, replace fast-closing valves, secure pipework or install correctly positioned arrestors.
How to prevent it happening again
- Keep system pressure controlled.
- Secure pipework properly during installations.
- Maintain appliance and toilet inlet valves.
- Use suitable arrestors where required.
- Investigate pump cycling and sudden valve closure.
Frequently asked questions
Is water hammer dangerous?
Severe or repeated hammer can damage valves, joints and appliances over time.
Why did it start after fitting a new appliance?
Modern solenoid valves can close quickly and reveal pressure or support problems.
Can lowering pressure stop water hammer?
It can reduce the force when pressure is excessive, but pipe support and valve behaviour may also need correction.
Need help with a water pressure problem?
Tell us which outlets are affected, whether the pressure is high, low or unstable, and when the problem started so we can help arrange the right diagnosis.