Boiler Making Banging Noises

Kettling (limescale on heat exchanger)

The most common cause of boiler noise in London. Hard water deposits build up on the heat exchanger, causing water to boil and steam before it circulates — creating a rumbling kettle sound. London water is among the hardest in the UK, making this particularly prevalent.

Sludge and magnetite in the system

Corroded particles from radiators accumulate in the boiler's heat exchanger, restricting flow and causing turbulent, noisy operation. System power flushing resolves this.

Low water pressure

Insufficient pressure causes cavitation in the pump — a banging or hammering noise. Check the gauge and re-pressurise if below 1 bar.

Pump failure or wear

A failing circulating pump makes rhythmic knocking or grinding noises. Usually needs replacing if bearings have worn.

Air in the system

Trapped air causes gurgling sounds and uneven circulation. Bleeding radiators and re-pressurising usually resolves minor cases.

Delayed ignition (banging at start-up)

A bang when the boiler first fires indicates gas building up before ignition — typically caused by a dirty or faulty burner. This is a gas safety concern and should be checked promptly.

Is a banging boiler dangerous?

A bang at start-up (delayed ignition) is a gas safety concern and should be investigated the same day. Kettling and gurgling are not immediately dangerous but indicate damage accumulating in the heat exchanger.

Why is my boiler so noisy in London?

London has some of the hardest water in the UK, making kettling from limescale extremely common. A scale inhibitor and annual servicing significantly reduce the problem.

Can I fix a noisy boiler myself?

You can bleed radiators to remove air and re-pressurise the system yourself. Beyond that, any work on the boiler itself requires a Gas Safe registered engineer.

My boiler makes a noise and then turns off — what's happening?

This suggests the boiler is overheating and triggering its thermal safety cutout. Most commonly caused by limescale on the heat exchanger or a failing pump. Call an engineer.