Boilers make noise. Which noise it is tells you a good deal about what is wrong.

Kettling: a sound like a kettle boiling

The classic one. Scale or sludge has built up on the heat exchanger, water is overheating in contact with it and turning to steam in small pockets. That is the noise.

It is not immediately dangerous but it should not be ignored, because it means the heat exchanger is running hotter than designed and that shortens its life. The usual answer is a power flush, and in hard water areas a scale reducer.

Banging or knocking when the heating starts

Often pipework expanding against a joist or a clip. Annoying rather than serious, and it can usually be traced and eased. If it comes with kettling, treat it as a circulation problem instead.

Gurgling or bubbling

Air in the system, or in cold weather a frozen condensate pipe. If the boiler has also locked out and it is freezing outside, check the condensate first.

Humming or vibrating

Usually the pump, either set too high or beginning to fail. Sometimes loose mountings.

A whistling or high-pitched noise

Often restricted flow: a partially closed valve, a blocked filter, or a pump struggling against a restriction.

What the noises have in common

Most of them come back to circulation and water quality. Sludge and scale cause kettling, contribute to pump failure and restrict flow. That is why a system with a magnetic filter and the correct inhibitor dose tends to stay quiet.

When to call someone

• Kettling, because it shortens heat exchanger life
• Any noise that has appeared suddenly and is getting worse
• Banging accompanied by the boiler locking out

Frequently asked questions

Is a banging boiler dangerous?

Usually not immediately, but kettling shortens the life of the heat exchanger and should be dealt with.

What is kettling?

Water boiling in small pockets against a scaled or sludged heat exchanger.

Will a power flush stop the noise?

If sludge or scale is the cause, it addresses it properly.

Why is my boiler noisier in winter?

It runs harder and longer, so existing restrictions show up more.

Want it sorted properly?

Anything past the free checks above needs a Gas Safe engineer with the right test kit. Ring Vantage on 01462 506374, any hour, any day of the year. You will get an honest arrival time rather than a comforting one, and the price before the work.