Why Is My Boiler Making a Banging Noise?

A loud banging or knocking sound from your boiler sometimes called "kettling" — is almost always caused by limescale, rust, or debris building up around the heat exchanger. As water tries to pass through the blocked area, it creates pockets of steam that cause the banging sound, similar to a kettle boiling.

Why it matters: kettling isn't just annoying it's a sign your boiler is working harder than it should, which reduces efficiency and can eventually damage the heat exchanger itself if left unresolved. In some cases, ignoring it can lead to a complete heat exchanger replacement, which is far more expensive than addressing the cause early.

What usually fixes it: in most cases, a powerflush clears the debris and built-up deposits from your whole central heating system, restoring normal water flow and stopping the noise. It's a non-invasive process that flushes your boiler, pipework, and radiators without needing to remove anything.

Other possible causes:

• Trapped air in the system (usually a simpler fix: bleeding your radiators)

• A failing pump

• Loose pipework causing vibration noise (a different, usually simpler fix)

Our advice: if the banging has started recently and is getting louder or more frequent, don't wait, the earlier a powerflush is carried out, the less chance of lasting damage. We offer powerflushing across Tunbridge Wells, Tonbridge, Cranbrook, Wadhurst, Goudhurst, and Hawkhurst, and can usually advise over the phone whether a powerflush is the likely fix based on what you're hearing. Get in touch for a free quote.