How to Fix Water Hammer in Pipes
Last updated: 7 September 2026
Secure loose pipes, check water pressure, and install water hammer arrestors.
Overview
Water hammer is a loud banging noise in pipes caused by water stopping suddenly. This guide covers diagnosing and fixing water hammer.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- Listen carefully around your home, especially when taps are turned off or appliances like washing machines finish filling, to pinpoint the exact location of the banging noise. Pay attention to which pipes or appliances seem to trigger the sound most often, as this will help you focus your efforts.
- Inspect all accessible pipework, particularly those in basements, utility rooms, or under sinks, for any pipes that are not firmly attached to joists or walls. Use appropriate pipe clips or clamps, ensuring they are the correct size for your pipes, to securely fasten any loose sections and prevent them from vibrating.
- Measure your mains water pressure using a pressure gauge, which can often be temporarily fitted to an outdoor tap or washing machine connection. If the pressure exceeds 4 bar (approximately 60 psi), consider installing a pressure reducing valve on your main incoming water supply to lower the overall system pressure.
- Locate the water inlet hoses for your washing machine and dishwasher, as these appliances are common culprits for sudden water stops. Screw a water hammer arrestor directly onto the appliances water inlet valve, then reattach the appliances hose to the arrestor, ensuring all connections are hand-tight and leak-free.
- Turn off your main water supply at the stopcock and open all taps, starting with the highest in your home and working down to the lowest, to completely drain the system. Once all water has run out, close all taps before slowly reopening the main stopcock to allow the system to refill gradually, pushing out any trapped air as it fills.
- If the banging persists after installing arrestors, check the pressure reducing valve on your main supply. A faulty valve can cause pressure spikes that contribute to water hammer.
- Check the water pressure at different times of day. If the pressure is significantly higher at night, this may indicate a problem with the mains supply that needs to be reported to your water company.
- Consider installing a pressure reducing valve on the main supply if your water pressure is consistently high. This will protect your entire plumbing system from pressure-related issues.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| Banging when tap turns off | High water pressure | Install a pressure reducing valve on the main water supply. This will lower the overall system pressure and reduce the impact of water hammer. |
| Banging when appliance stops | Solenoid valve slam | Install water hammer arrestors on the supply hoses of the affected appliance. This absorbs the shock of the water stopping suddenly. |
| Banging during use | Loose pipes | Secure loose pipes with pipe clips or clamps. Check all accessible pipework and add fixings where needed. |
| Banging at night | High mains pressure at off-peak times | Check the water pressure at different times of day. If the pressure is significantly higher at night, report this to your water company. |
Frequently Asked Questions
What causes water hammer?
Water hammer is caused by water moving at high speed being suddenly stopped by a tap or valve closing. This creates a shock wave that travels through the pipes, causing a banging or knocking sound.
Can water hammer damage pipes?
Yes, water hammer can damage pipes over time. The repeated shock waves can cause joints to loosen, pipes to leak, and in severe cases, pipes to burst. It is important to address water hammer promptly.
How do I install a water hammer arrestor?
To install a water hammer arrestor, turn off the water supply, disconnect the appliance hose, screw the arrestor onto the valve, and then reattach the hose to the arrestor. Ensure all connections are tight and leak-free.
What is a pressure reducing valve?
A pressure reducing valve is a device that reduces the incoming water pressure to a safe and consistent level. It is typically installed on the main water supply pipe and can help prevent water hammer and other pressure-related issues.