Fixing water hammer (banging pipes)
Water hammer—that alarming bang or clang when you turn off a tap—is one of the most common plumbing complaints we hear about, and the good news is it's usually straightforward to fix. It happens when water moving through your pipes suddenly stops, creating a pressure shockwave that reverberates through the pipework and can sound quite dramatic. You'll typically notice it most when turning off a washing machine, dishwasher, or kitchen tap quickly, though it can occur anywhere in your system. Most cases are down to loose pipes, partially closed valves, or mains pressure that's too high—all things you can address yourself without calling out an engineer. However, if the banging is severe, accompanied by leaks, or occurs on a heating system that's already showing signs of trouble, it's worth getting a qualified plumber to take a look.
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Most likely cause & what to check
Water hammer is caused by water stopping suddenly in a pipe, creating a pressure wave that bangs the pipework.
First, check for loose pipes — pipes that aren't clipped to the wall or joists will rattle when water flows. Secure any loose runs with additional pipe clips.
Check that all stop taps and isolation valves are fully open. Partially open valves restrict flow and increase water hammer.
Reducing the incoming mains pressure can significantly reduce water hammer. A pressure-reducing valve (PRV) can be fitted on the mains supply.
Fitting a water hammer arrestor on the worst-affected supply pipe absorbs the pressure wave. They're screwed onto the supply pipe near the problem tap.
If the problem is on the central heating system, check the pump speed setting — a high setting can cause pipework noise.
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Frequently asked questions
Is water hammer dangerous to my pipes?
Water hammer itself won't cause immediate damage, but repeated pressure surges can gradually weaken pipe joints, solder connections, and fittings over time, potentially leading to leaks. Addressing it early prevents costly damage down the line and helps your plumbing system last longer.
Why is my water pressure so high in the first place?
Mains pressure varies across the UK depending on your location and your water company's supply. If your home is at the bottom of a hill or served by a strong pressure zone, you could naturally have higher pressure than the recommended 2-3 bar. A pressure-reducing valve installed at your incoming supply is the permanent solution.
Can water hammer damage my central heating boiler?
Sustained water hammer in a heating system can stress the boiler and pipework connections, so it's worth tackling. Check your pump speed setting first—many systems are set too high—and if that doesn't help, fit an arrestor on the affected circuit or consult a Gas Safe engineer.
What's the difference between water hammer and just noisy pipes?
Water hammer is a sudden loud bang that happens when you turn off a tap, whereas general pipe noise is often a rattle or hum from loose clips or vibration during normal water flow. The fixes overlap, but water hammer specifically requires dealing with pressure waves, so check for loose pipes first, then look at pressure and valves.