Noisy Pipes: Water Hammer, Banging and What Causes It

Pipe noises range from mildly irritating to genuinely alarming. The reassuring news is that most pipe noises are benign and fixable, and only a few indicate a serious problem. This guide covers the most common types and what causes them.

Water hammer — the loud bang

Water hammer is the sharp banging or thudding sound that occurs when a tap or valve is closed quickly. The moving water column, suddenly stopped, creates a pressure wave that hammers through the pipework and sometimes into the walls.

What causes it: Modern lever-action taps, ball-float valves in cisterns, solenoid valves in dishwashers and washing machines all close very quickly compared to older screw-turn taps. The sudden stop creates the shock wave.

Where to look:

• Ball valve in the toilet cistern: if the bang happens after every flush, the cistern ball valve is closing too fast as the cistern refills
• Washing machine or dishwasher: bang when the solenoid valve closes at the end of a fill cycle
• General pipework: bang when any tap or valve closes quickly

How to fix it:

Cistern ball valve: Replace with a modern equilibrium ball valve or a quiet-fill valve. These close gradually under internal water pressure rather than slamming shut. This is a straightforward DIY replacement.

Washing machine/dishwasher: Fit a water hammer arrestor to the supply pipe. These are spring-loaded devices that absorb the pressure wave. Available from plumber’s merchants, they fit between the machine hose and the supply valve.

General pipework: Ensure pipes are properly clipped to joists and walls — a loose pipe amplifies the hammer effect by vibrating freely. Add pipe clips every 600mm for horizontal runs, 900mm for vertical.

Ticking or clicking when the heating comes on

A ticking or clicking sound that starts when the heating system fires up and gradually fades is almost always thermal expansion of pipes. As copper heats up, it expands and moves slightly against the clips or the joist notches it passes through.

Cause: Normal thermal expansion. Not a defect.

When it becomes a problem: If the clicking is very loud or accompanied by cracking sounds, a pipe may be pinched at a notch or clip that’s too tight. This is worth investigating because a pinched expanding pipe can crack over time. Apply insulating tape to the pipe at the constriction point to allow silent expansion.

Rumbling or vibrating from the boiler

A rumbling, vibrating, or kettling sound from the boiler is almost always caused by limescale on the heat exchanger. Hard water deposits scale on the copper surfaces, reducing heat transfer efficiency. Water trapped under the scale superheats and vaporises momentarily, causing the rumbling (the process is exactly the same as a kettle “furring up”).

Cause: Limescale in the heat exchanger.

Impact: The boiler uses significantly more gas to achieve the same heat output. Fuel bills rise. The heat exchanger eventually fails prematurely.

Fix: A descaling treatment by a Gas Safe registered engineer. Chemical descalers can clear mild scale; severe scale may require heat exchanger replacement. A powerflush of the whole system removes scale from the radiators and pipe runs as well as treating the boiler.

Hissing from the radiator or pipes

A hissing sound from a radiator — particularly near the bleed valve or TRV — usually means air trapped in the system. The hiss is the sound of water flowing past the air pocket.

Fix: Bleed the radiator. See our radiator bleeding guide.

A constant hissing from a pipe joint or fitting may indicate a small water leak with water escaping under pressure. Investigate visually — any damp patches, staining, or dripping?

Whistling or whining from the boiler or pipes

A high-pitched whistle or whine when the system is running is often associated with a failing pump, a partially blocked strainer, or a pump speed that’s set too high for the system.

Pump speed: Most circulating pumps have multiple speed settings. If the speed is too high for the system, the turbulent flow creates noise. Try reducing the pump speed by one setting.

Strainer blockage: Most boiler returns have a magnetic filter and/or a strainer. If this becomes very blocked with sludge, restricted flow creates a whistling sound. Clean or replace the filter.

Pump failure: A bearing starting to fail creates a persistent whine that gets worse over time. A plumber can assess whether the pump needs replacement.

Gurgling in drains

Gurgling sounds from sink or bath drains — particularly when a toilet is flushed nearby — indicate air movement through the system caused by drainage venting issues or partial blockages. See our sewer smell guide for a full treatment of vent and drain issues.

Banging from the attic tank (older systems)

Properties with gravity-fed central heating have a header tank in the loft. If you hear periodic banging from the loft, the ball valve in this tank may be chattering — vibrating as it refills. This is the same mechanism as water hammer in a cistern, and the fix is the same: replace the ball valve with a quieter equilibrium type.

When pipe noise indicates a serious problem

Most pipe noises don’t indicate danger, but call a plumber if:

• Banging is accompanied by visible movement of a pipe
• You can hear hissing from inside a wall and there’s no obvious source
• A pipe that was previously quiet has suddenly become very noisy (suggests a joint has partially failed)
• Noise is accompanied by any water staining, damp, or reduced water pressure