Boiler Making Strange Noises? What Banging, Whistling and Gurgling Mean

Banging or clunking

A banging noise as the heating starts often means trapped air or sludge in the system, or pipework expanding against a joist. Start by bleeding your radiators. If banging continues, a build-up of sludge may need a power flush.

Whistling or "kettling"

A whistling or rumbling like a kettle boiling usually means limescale or sludge has built up on the boiler heat exchanger, causing water to overheat and steam. Kettling makes the boiler work harder and shortens its life, so it is worth sorting promptly with a service and, if needed, a flush.

Gurgling

Gurgling is typically trapped air or low pressure. Check the pressure gauge (1–1.5 bar cold is normal) and top up if needed — our guide on boiler pressure loss walks through it. In winter, gurgling on a condensing boiler can also mean a frozen condensate pipe.

When a noise is urgent

Some noises should never be ignored. Turn the boiler off and call an engineer immediately if you hear tapping or banging combined with a smell of gas, or if a carbon monoxide alarm sounds. Carbon monoxide is odourless and dangerous — the NHS explains the symptoms and what to do.

For anything you are unsure about, we are Gas Safe registered and cover the whole region — get in touch and we will take a look.

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