Fixing water hammer (banging pipes)
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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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