It can be a little disconcerting to find your boiler is making noises. In this article, we’ll be discussing what noises your boiler should be making, and we’ll try to give some clues about what could be causing other sounds.

Sometimes, you might be able to fix the problem yourself, but if it has suddenly started giving off strange noises, it’s always safer to call out an engineer to have a look at it.

What noises should a boiler make?

Boilers are machines, so we can’t expect them to be completely silent. Boilers exist in two states – active and passive (on standby). When they’re active, they’re boiling mains water by circulating their own water over a flame, then transferring that heat to the mains water flowing to taps or a cylinder.

As you can imagine, that requires moving parts, pipework, pumps, valves and switches. It makes the rumbling and clicking sounds you’ll be familiar with if you turn on a hot tap with a combi boiler, if your system boiler is filling the cylinder, or if the central heating comes on.

In the passive state, boilers are still switched on; they’re just not boiling water. So don’t be surprised to hear faint noises – they could be a slight buzz of electronics or parts cooling down after being heated.

Also, many boilers have a pre-heat setting, which keeps the circulated water at a certain temperature so that hot water is available when needed. That means it will turn itself on from time to time, even though it’s not being used. That’s a design feature and is completely normal.

What boiler noises suggest a problem?

Some noises, however, are signs of potential problems. They usually start when the boiler is actively heating water, as that’s when parts and water are moving within the system. Let’s look at some of the common sounds and what might be causing them.

Tapping or knocking sound

If your boiler is making a tapping sound, this is called “kettling” and is usually caused by a build-up of limescale in the pipework. As a user, there isn’t much you can do in the short term – it will probably need parts to be replaced or cleaned, usually the heat exchanger. However, fitting a filter and adding specialist chemicals to your system will dramatically slow down the build-up of limescale in the future. If you live in an area of hard water, perhaps it’s something to consider.

Gurgling or popping

Gurgling or popping sounds are almost always caused by air in the system. Fortunately, there’s usually a simple way to solve this: bleeding a radiator.

Turn your heating off and locate the bleed valve on your radiator – it’s often on the side at the top, but could be round the back, facing the wall.

Untighten the valve just a little with the bleed key (or a spanner or screwdriver for some systems) until you’ll hear a hissing sound – that’s air escaping.

When the hissing stops and water starts coming out, the job’s done, so quickly tighten the valve. You might need to top up the water pressure with the valves on the boiler – check your user manual or online for details.

If the gurgling continues, try a few other radiators, but if that doesn’t work, call the professionals.

Banging or rattling

If there's a banging or rattling sound coming from inside the boiler, it’s most likely to be something mechanical, probably the pump.

It might just need tightening up, but it could require a new pump. Either way, if your boiler is rattling or banging, you should have it looked at by an engineer.

Duffy Heating: Serving Dublin

If you’re in the Dublin area, we’re here to help diagnose, fix or replace your noisy boiler. If you’re in any way concerned about yours, just get in touch so we can pop round and have a look, even if it’s just to put your mind at rest.

Published: 13 July 2021

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