Why is my boiler making a banging noise?

A boiler that bangs, knocks or rumbles is telling you something specific. Most of the time it is not dangerous on its own, but it is a symptom of a fault that gets more expensive the longer it runs. Here is how to work out which noise you have.

Kettling: a rumble or a boiling kettle sound

This is the most common one by a distance.

Limescale and corrosion debris build up on the heat exchanger. Water gets trapped against the hot metal, flashes to steam and collapses again, and that is the rumble you can hear. Greater Manchester sits in a soft to moderately hard water area, so scale is less aggressive here than in the south, but corrosion debris from steel radiators causes exactly the same effect.

Left alone, kettling overheats the heat exchanger and shortens its life considerably. The fix depends on how far it has gone: sometimes a chemical clean and inhibitor is enough, and sometimes the system needs a full power flush to clear the debris out of the radiators as well.

Banging when the heating starts up

A single loud bang shortly after the boiler fires is usually delayed ignition. Gas builds up in the combustion chamber for a moment before it lights, and it ignites all at once.

This one is different from the others. It is a combustion fault and it needs a Gas Safe registered engineer to look at it, not a DIY fix. Do not keep running the boiler and hoping it settles.

Knocking and creaking as pipes warm up

If the noise follows the pipework rather than coming from the boiler itself, it is usually thermal expansion. Copper expands as it heats and if a pipe is clipped too tightly, or is passing through a tight notch in a joist, it grabs and releases with a knock.

It is annoying rather than serious. Easing the clip or the notch fixes it, though getting at the pipe is often the harder part of the job.

Gurgling

Gurgling normally means air in the system, and air usually means one of two things: the system has been topped up or drained recently, or you have a small leak somewhere drawing air in as it loses water.

Bleeding the radiators is the first step. If the gurgling comes back within a few weeks, you have a leak, and that is worth reading our page on boiler pressure that keeps dropping.

Humming or vibrating

A hum that rises and falls with the heating is often the pump, either running at too high a speed for the system or beginning to fail. Sometimes it is a loose bracket resonating against a wall. Both are straightforward to sort once someone has heard it running.

What you can safely check yourself

• Is the system pressure in the normal band, usually between 1 and 1.5 bar cold?

• Are the radiators cold at the top, which points to air?

• Does the noise happen on hot water only, heating only, or both?

Knowing which of those applies genuinely narrows it down before an engineer arrives.

When to stop and call someone

Turn the boiler off and ring us if you have a bang on ignition, if you can smell gas, or if the boiler is locking out repeatedly alongside the noise. If you smell gas, ring the National Gas Emergency Service on 0800 111 999 first.

For everything else, book it in rather than living with it. A noisy boiler is a boiler working harder than it should.

Our boiler repair and central heating repairs pages explain how we diagnose it, and an annual boiler service is what stops most of these noises starting in the first place. We work across Manchester, Salford and the surrounding towns.

Ring 0161 515 9977 and describe the noise. It is usually enough for us to know what we are walking into.