Whether you’re a renter or a homeowner you’ve probably never paid much attention to your boiler, aside from occasional pressure top-ups or annual service checks. In most homes, the boiler simply hangs on the wall, minding its own business and doing the vital job of providing us with heat and hot water.

But as with any electrical appliance, when things go wrong, they can go wrong in ways we don’t expect. Chances are, you’re here because your boiler has been making strange noises lately. And to help you and the many others who have experienced this, we’ve created a soundbank of audio clips along with explanations of what they mean. This should help you diagnose your boiler problem and will also tell you if you can sort out the issue yourself or when you’ll need an engineer to take a look.

Simply click on the sound icons below to check whether they sound like the noises your boiler makes and find out how you can solve the underlying problem. Please note we’ve amplified some of the sound recordings for illustrative purposes.

Boiling kettle
Mystery sound 1
Mystery sound 2

Rattling noises

If your central heating makes loud rattling noises, that usually indicates there are loose objects shaking or vibrating against one another, but if that’s not the case, there are a few more reasons why this could happen.

Sometimes, rattling noises from a boiler are the result of air in the pipework. You can get rid of the excess air in the system by bleeding your radiators and, as this is a simple thing to do, you won’t need to call an engineer. Head over to our guide on how to bleed radiators, and make sure you also check out how to repressurise your boiler, as it’s likely that the pressure in your boiler will drop after bleeding your radiators.

If you’ve bled your radiators but still hear the rattling noise, it could be a loose valve. Try locating the source of the sound, and simply tighten any loose valves on your radiators to stop the annoying sounds. Finally, check whether the rattling noises come from any pipes that haven’t been clipped well. Unclipped pipe work is often the cause for this kind of noise.

If you’re sure that it’s not a radiator valve that has gone rogue and all pipework seems to be in order, it could be a faulty pump or valve — especially a failing non-return valve. If you’ve checked the other possible sources and can’t find the culprit, you’ll need an engineer call-out to get this sorted.

Loud humming noises

Electric water heaters can emit a humming noise: it’s easy to fix this yourself by tightening the heating element. Water heaters can also cause rumbling noises due to bits of sediment, rust or limescale heating up and expanding within the cylinder.

Rumbling noises can also stem from very high pressure. If the incoming main water supply has too much pressure, valves inside your house can hum or whine, so it’s important to check if you need to readjust. If you also encounter the same humming noise when you close a tap, your boiler is fine, and it’s the washers on the tap that could need replacing.

It may also be the case that your pump is set too high. As a result, the heated water in your central heating system travels too fast around the pipework, which can cause a number of problems, including vibrations, trickling and humming noises.

Finally, a persistent hum can also be caused by the fan inside your boiler and, in particular, by the bearings in the fan. If you can’t pinpoint the reason for the humming noise at this stage, it’s time to get an engineer to check it out.

Vibrating noises

Vibrations in your boiler can be caused by a number of factors. These can include a malfunctioning pump shaking inside the casing, or as we’ve described above, an incorrect setting for your pump like having it too high.

It can also be caused by a build-up of sludge inside the boiler. A build-up of this kind is potentially dangerous as the excess sludge can cause overheating, so if you hear this sound, it definitely needs the attention of a qualified engineer.

Boiling kettle noises

It’s pretty safe to assume that this noise is caused by either kettling or trapped air inside the central heating system. First, try to bleed your radiators to remove the air.

This is a very easy process and doesn’t need an engineer call-out, but don’t forget to check and adjust your boiler’s pressure afterwards.

If you’ve bled your radiators but the noise persists, kettling could be the culprit. Kettling is exactly what it sounds like: noises that sound like a whistling of water coming to the boil. It’s caused by an accumulation of limescale or corrosion debris in the system, sometimes within the boiler itself.

Unfortunately, this is a natural process and happens more often in areas with hard water. If the limescale affects the heat exchanger itself or the area around it, water flow becomes restricted. The trapped water will heat up too much, start boiling and eventually turn into steam and expand, which is why you may hear a whistling noise. It sounds simple but you won’t be able to fix this one yourself, so you’ll need it to be checked out by a qualified engineer.

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