Why Is My Boiler Making a Strange Noise?

Boilers are not silent, but they should not be loud either. If your boiler has started banging, whistling, gurgling, or humming, it is trying to tell you something. Different noises point to different problems, and some are more urgent than others.

Banging or clunking

A banging sound from inside the boiler is usually kettling. This happens when limescale or sludge builds up on the heat exchanger, restricting water flow and causing it to overheat in small patches. The water turns to steam, and the steam bubbles collapse with a bang.

A powerflush will clear the sludge and usually fixes the problem completely. Left untreated, kettling reduces your boiler's efficiency and can shorten its lifespan significantly.

Banging from the pipes rather than the boiler itself is usually thermal expansion. Metal pipes expand when they heat up and can knock against joists, floorboards, or wall clips. Annoying but not dangerous.

Whistling or high pitched noise

A whistling boiler is sometimes called "kettling" too, though it is slightly different from banging. It usually means water flow is restricted somewhere, often in a thermostatic radiator valve that is partially closed or a blockage in the system. Try opening all your TRVs fully and see if the noise stops.

Gurgling

Gurgling usually means there is air trapped in the system. The fix is simple: bleed your radiators. Start with the radiator furthest from the boiler and work your way back. If the gurgling is coming from the boiler itself rather than the radiators, there may be a more serious circulation issue.

Humming

A persistent hum from the boiler is often the pump running too fast. Most modern pumps have adjustable speed settings. Turning the pump speed down one notch can eliminate the hum without affecting performance. If the hum is very loud or vibrating, the pump bearings may be worn and it might need replacing.

Clicking or ticking

Gentle clicking as the boiler fires up and shuts down is completely normal. That is the ignition system and the metal components expanding and contracting with temperature changes. Nothing to worry about.

When to be concerned

Persistent banging, loud whistling, or any noise that is getting worse over time should be investigated. These are signs of a developing fault that will only get more expensive to fix if ignored.

Need help with your boiler? Our Gas Safe registered engineers cover the North East. Get in touch today or call 07579 760536.