Boiler making a banging, whistling or gurgling noise?

Boilers are not silent, but they are consistent. A noise that is new is a noise worth understanding. Here is what each one usually means.

Banging or kettling

A sound like a kettle boiling, sometimes with a bang. This is limescale or sludge on the heat exchanger. Water is getting trapped, overheating, and flashing to steam.

It is not immediately dangerous but it is not harmless either: the boiler is working far harder than it should, burning more gas, and the exchanger is being stressed every time it happens. Often a power flush and a chemical inhibitor sorts it. If the scale is bad enough, it has already shortened the boiler's life.

Whistling

Usually air in the system, or a pump running faster than it needs to. Bleeding the radiators is worth trying first, and it is a ten-minute job you can do yourself with a bleed key.

Gurgling

Air again, or low pressure, or a frozen condensate pipe if it has just turned cold. That last one is the most common winter call-out an engineer gets, and it is fixable in twenty minutes with warm water on the outside pipe.

Vibrating or humming

Often the pump, sometimes loose brackets. A humming boiler is usually a mechanical issue rather than a combustion one, which makes it less urgent, though still worth a look.

The one that means stop

If you can smell gas, or you hear a loud roaring inside the casing, turn the boiler off, do not touch any electrical switches, open the windows, and ring the National Gas Emergency Service on 0800 111 999. That is not a repair-or-replace decision, that is a leave-the-house decision.

The same applies if your carbon monoxide alarm sounds. If you do not have a CO alarm next to your boiler, buy one today - they cost about £20 and they are the reason people wake up.

What the noise usually tells you about age

Kettling in particular is a symptom of years of build-up. If your boiler is over ten and it has started singing to you, it is telling you something about how much life is left in it.