Banging or Knocking Pipes — Causes and Fixes

Water hammer

When a tap or valve closes quickly, the sudden stop of flowing water creates a pressure shockwave — the classic 'bang' after turning off a tap. Common with solenoid valves in dishwashers and washing machines.

Thermal expansion in copper pipes

Copper pipes expand when hot water flows through them. If they're tightly clipped or pass through tight holes, expansion causes ticking or knocking as the pipe moves.

Loose pipe clips

Pipe clips that have come away from the wall or ceiling allow pipes to move and knock against the structure. Usually visible in exposed areas like under floorboards or in airing cupboards.

Practical checks and next steps

If you can see the pipes that are making noise and they're loose in their clips, refastening them is DIY. Water hammer — banging when taps are turned off — needs a plumber to fit an arrestor or pressure-reducing valve.

• Note when it happens — turning off a tap, heating coming on, or random.
• If random: check visible pipework for loose clips. Refasten or add additional clips.
• If on tap turn-off: this is water hammer — reduce the flow velocity or fit an arrestor.
• If on heating startup: thermal expansion — check pipe clips aren't too tight at wall penetrations.
• Persistent or worsening banging that can't be traced to a visible cause: call a plumber.