Is your boiler making noises?
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.
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.
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.
If your boiler makes loud banging and/or popping sounds, you can be pretty sure that this is also due to kettling. As described above, kettling is caused by a build-up of mineral deposits or sludge in the heat exchanger.
This build-up happens more frequently with older cast-iron heat exchangers and in areas with hard water. Occurring when the flow of water through the heat exchanger has slowed or become blocked completely, the kettling process causes the water to boil and produce steam, which is another sound you may hear alongside the characteristic banging.
In more serious cases, big air bubbles start to pop and create such loud banging noises that it can feel like the boiler is going to fall off the wall. It’s an unpleasant, shocking sound, but rest assured that it’s not going to happen: kettling cannot make your boiler explode! It’s best to have an engineer come and take a look at your boiler, though, because build-up isn’t something you can easily fix with a DIY solution.
Dripping or gurgling noises
A gurgling or dripping sound can sometimes be heard coming from radiators and pipework. The most common reason for this is trapped air in your boiler system that mixes with the water, though there shouldn’t be any air present at all in your boiler.
Trapped air is nothing to worry about and can easily be resolved by bleeding your radiators. While not dangerous, you should be aware that this trapped air stops the heat from fully radiating throughout the room, which will cause your boiler to use more gas and stay on for much longer than it usually would. As this can lead to increased heating bills in the colder months, we’d recommend bleeding your radiators as soon as you hear consistent tapping or gurgling noises from your boiler.
Occasionally, gurgling noises can also be caused by a frozen condensate pipe. You can resolve this by unfreezing the pipe: you should do this as quickly as possible to avoid further damage to your boiler.
Another noise you may hear that is characteristic for kettling is a tapping sound, especially when turning on your boiler. Kettling noises are commonly caused by a build-up of limescale or corrosion debris on the surfaces of the heat exchanger. This build-up can restrict the flow of water and cause localised boiling of water, which can cause hot water to turn into steam.
The noise itself is usually due to a build-up of sludge in your radiators or pipes, which becomes louder as the pump circulates the water in the central heating system. If you hear consistent tapping noises and you think it might be kettling, it’s best to call out an engineer to take a look at your boiler, as it’s not possible to fix this by yourself.
Air bubbles trapped in the water of your central heating system expand and collapse, which can cause clicking noises similar to this tapping sound. Live in a hard water area? Be especially aware of kettling as it’s more likely to occur with the sediment-rich water in your system.
A noise that sounds like a drone, an aeroplane or even a foghorn (as demonstrated in this example) is characteristic of a pump that’s on its way out. There’s a variety of causes for this, such as a simple mechanical pump failure or air and debris caught in the boiler’s impeller. When one part of a boiler system starts to break, this can very easily escalate to other areas of your boiler, and spread to affect your home at large.
Once a pump in your boiler is affected, you should call out an engineer to properly assess the issue and potentially replace the faulty pump. If there is significant damage to the internal system due to mechanical failure, you might also be advised to replace your boiler instead of repairing it.
Mystery noise 1
It’s unlikely, but it never hurts to check: if your moggy is missing and your boiler is making this noise you should look and see if your pet hasn’t crawled into the boiler cupboard and potentially got stuck in the piping.
Cats like to sleep in warm, insulated places, and what’s warmer or cosier than your boiler in winter? This doesn’t need an engineer call out unless your pet has done some serious damage in their attempt to get out, but it might need a bit of bravery to retrieve them.
Mystery noise 2
Unless your boiler is all the way up in the attic, that’s not the sound of bats you’re hearing. It’s the unfortunate noise of someone playing the violin — and not doing a good job of it. Kettling noises sound quite distinct from other high-pitched noises such as violins and other string instruments, so if you’re hearing this then it’s likely that one of your neighbours is attempting to play a tune.
While this doesn’t need an engineer call out, we recommend investing in a good pair of earplugs.