Why Is My Boiler Making a Noise?
Why Is My Boiler Making a Noise?
Boilers are probably the most essential appliance we all have in our homes, given that they control our central heating and hot water. Because they’re so important, it’s normal to worry if your boiler makes unusual noises.
Boilers are complicated appliances that perform a range of both manual and automatic functions. They heat water and pump it around your central heating system when you activate them, and they also perform background tasks. For example, after a boiler has heated your house to the right temperature on the thermostat, it might automatically keep the pump running to dissipate heat. Otherwise, a boiler might do another background task like springing on to keep a small amount of water preheated for immediate use.
In most cases, the noises boilers make are actually just normal operating noises. Quiet clicks, humming and hissing noises usually mean a boiler is just doing what it’s supposed to do. This isn’t always the case, however. Other noises, like banging, whistling, gurgling or droning are unusual noises that should be investigated.
In this article, we’ll look at some common noises boilers make and explain whether they could be a sign of trouble.
You can help maintain your boiler’s health and efficiency by listening to the noises it makes, but you should be careful. Boiler problems can be difficult to diagnose by sound alone. If you are in any doubt about your boiler, we recommend you hire an engineer who is qualified to work with your boiler system. All gas boilers and accessories must be installed and maintained by a Gas Safe registered engineer.
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Reasons for a boiler making noise when not in use
Your boiler is never really turned off. Modern boilers on standby are ‘on’ in that they’re connected to the mains and may carry out background functions like pressure maintenance, pump-overrun, or pre-heating. But not all boilers behave the same, combi boilers with eco modes, for example, can remain completely idle unless activated.
If a boiler makes noises when it’s not in use, this doesn’t always mean something’s wrong.
Here are some of the common reasons why boilers make unexpected noises when they’re not in use:
Expansion and contraction of metal parts in a boiler
A boiler's internal mechanism is made of metal, which naturally expands and contracts as it heats up and cools down during normal use. This process can cause soft clicking or popping sounds, which are completely normal. Similar noises may also come from connected components, such as pipes, radiators or other parts of your home's heating system.
Residual boiler pressure
Residual pressure is pressure left inside the boiler system after it's been shut off. Purpose designed pressure relief valves can automatically release water that’s under excess pressure, creating hissing and other noises, and if these are releasing pressure frequently, it could indicate an issue, these are safety failsafes, not part of normal functioning.
Sometimes, pressure levels above standard boiler pressure put strain on a boiler system. It is normal, however, for some boilers to occasionally release excess pressure.
Boiler leaks
If a boiler has an internal leak, this can be another reason for a boiler making noise when not in use. Leaks are a major problem, and water that leaks inside a boiler can damage electrics and corrode metal parts.
Dripping sounds aren’t always a sign of a leak. Some boilers make dripping noises as part of normal operation.
Water Hammer
A water hammer occurs when water flowing through a pipe suddenly stops or changes direction. This creates a loud bang and a shockwave that can damage a boiler system. Addressing a water hammer issue may involve checking pipe installation, adding air chambers or adjusting water pressure.
Water hammers can happen when a boiler is in use and when it’s not in use.
Normal operating boiler noises
Most of the time when boilers make quiet, regular noises, it’s just part of their normal operation.
Boilers have valves and electrical and mechanical parts that make noise when they’re working. Boilers, pipes and radiators all expand and contract with temperature changes as well, which can create noise. These noises can happen when a boiler’s actively heating water and when it’s not.
If your boiler is making any of the following noises, it could just be part of the way it normally works.
Clicking and popping noises
As we just mentioned, boilers and component parts all expand and contract as they change in temperature with normal use. This can create clicking and popping noises. These noises can happen when a boiler is in use and when it’s not. Clicking sounds can also happen when components work, such as when the pilot light comes on to get a boiler started.
Quiet clicking and popping noises usually aren’t a problem. If you hear loud noises, however, this could be a sign of trouble.
Hissing noises
Some boilers are fitted with pressure release valves that activate to release water or steam when the water pressure is too high. These are an important safety mechanism and are part of normal boiler operation. If one of these valves activates, you might hear a quiet hissing noise for a few seconds.
Hissing boiler noises can happen when the heating’s on and when it’s not.
Humming noise
It’s quite normal for a boiler to make a quiet, background humming noise when the heating’s on. This sound is created by the pump, and it’s a sign that your boiler is working normally. The pump works to pump water into the boiler for heating and to the radiators and hot water outlets in your home. Some boilers will also continue to pump water when the heater is deactivated.
Sometimes, a quiet humming noise can be a sign of a problem. Humming that carries on when a boiler isn’t activated is sometimes a sign of a pressure problem, a faulty pump or a faulty fan.
Unusual boiler noises that should be investigated
Some noises that come from boilers are a sign that something might be wrong. If boilers make loud banging, rumbling or vibrating noises, this is a sign there’s some kind of mechanical problem. Whistling, gurgling, whooshing, droning and dripping are other signs of a possible problem.
All work on gas and LPG boilers must be completed by a registered Gas Safe heating engineer, and all oil boilers should only be worked on by a competent OFTEC registered technician. Work on other boilers, including electric boilers, should be completed by a competent and suitably qualified NICEIC registered plumber.
High-pitched whistling
If your boiler is making a high-pitched whistling noise, this is a sign there’s a problem. This is usually the result of something called ‘kettling’.
Kettling happens when the flow of water around the inside of a boiler is restricted for some reason. Water trapped in the heat exchanger boils and creates steam. As steam escapes, it creates a whistling noise like an old fashioned kettle. In some cases, kettling also causes banging noises.
Some causes of restricted water flow are:
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Limescale build up
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Faulty thermostat
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Faulty pump
Limescale can be cleaned off by a professional, but a faulty thermostat or pump will need replacing. A properly functioning water filter can help prevent water flow problems.
Kettling is a common reason for a boiler making noise when the heating’s on. It’s potentially dangerous, and it’s best to get a qualified boiler engineer to take a look.
And as mentioned above, All work on gas and LPG boilers must be completed by a registered Gas Safe heating engineer, and all oil boilers should only be worked on by a competent OFTEC registered technician. Work on other boilers, including electric boilers, should be completed by a competent and suitably qualified NICEIC registered plumber.
Gurgling or bubbling
Gurgling and bubbling noises usually happen when there’s air trapped inside the boiler system. These noises can come from radiators or the boiler itself, although it’s more likely you’ll notice them coming from radiators.
Trapped air isn’t usually a serious problem. You can fix this problem yourself by bleeding your radiators.
Whooshing noise
Another common reason for a boiler making noise when the heating is on is when the air intake, flue guard or filter is blocked. This will usually result in a continuous whooshing noise.
If you think your boiler’s air intake or filter is blocked, you can inspect it for obvious signs of blockage. If you are unable to find any obvious blockages, it’s best to call a qualified engineer.
Drone noise
Another reason your boiler might be making noise when the heating is on is if the pump is faulty. This normally results in a droning noise, or a noise like an aeroplane taking off. The only solution to this problem is to fit a new boiler pump.
This is a job for a qualified boiler engineer. Do not ignore this problem because a faulty pump could cause other problems.
Bangs or booms
Loose, malfunctioning or broken internal boiler components can cause a variety of noises. These issues can cause loud and unsettling noises like banging or rattling that are different to the noise from a water hammer. As well as problems with internal components, problems with external components like boiler mounts or pipes can also cause similar noises.
You may be able to tighten loose mounts around your boiler or on external pipes. However, broken parts and any problems with internal parts should be looked at by a competent and suitably qualified engineer.
As we mentioned earlier, kettling can also result in banging noises.
Loud humming or vibrating
If you’re asking why is my boiler making a loud vibrating noise or a loud humming sound, this could be because there’s a problem with the fan or the fan bearings. You’ll need to get a competent and suitably qualified engineer to fit a new part if you have this problem.
Dangers of ignoring loud noises in your boiler
Faults with boilers aren’t always an immediate safety concern. Boilers are built with safety mechanisms that shut them down before they become dangerous. In most cases, the main risk of ignoring a faulty boiler is further damage to the boiler.
This isn’t always the case, however. Some problems with boilers are a sign of danger. You should always be careful if you think there is a fault with your boiler. We recommend using a competent and suitably qualified plumber if you think your boiler might have a serious problem.
When should I worry about boiler noises?
You should worry about boiler noises if you hear any of the noises we’ve identified as unusual noises that should be investigated further.
Sometimes an old boiler will need replacing with a new boiler. Most of the time, however, you might just need to pay for replacement boiler parts.
What to do if your boiler is making a noise
Sometimes people can investigate problems with their heating systems themselves.
If you hear gargling sounds, for example, it probably just means there’s air trapped in your heating system. You can fix this yourself by bleeding your radiators. Another fix you can do yourself is adjusting the pressure in your boiler.
You might also be able to manually repair or secure loose components, mounts or fixings to secure your boiler, pipes and other accessories in place.
Seek professional help if you are unsure
Other problems will need professional attention. Many of the problematic noises mentioned in this article need the attention of a suitably qualified boiler engineer. Problems with complicated parts, such as smart heating system components, will always need professional attention. Concerning noises that continue should always be looked at.
If you are at all unsure why your boiler’s making a noise, you should call a competent and suitably qualified engineer. All work on gas and LPG boilers must be completed by a registered Gas Safe heating engineer, and all oil boilers should only be worked on by a competent OFTEC registered technician. Work on other boilers, including electric boilers, should be completed by a competent and suitably qualified NICEIC registered plumber.
Boiler making noise key takeaways
Having a functioning boiler is absolutely essential. If your boiler starts making unusual noises, it might make you worry.
Boilers make a variety of noises, and they can make noises even when they’re not heating water. Quiet clicks, humming and ticking aren’t usually a sign anything’s wrong. However, loud noises and any of the problematic noises mentioned in this article might be a sign there’s a problem.
If you suspect there might be something wrong with your boiler, it’s best to call out a competent and suitably qualified engineer.
Faulty boilers can usually be repaired, and it’s unlikely you’ll need to find a replacement boiler, particularly if you carry out repairs promptly and keep your boiler in good condition. Nevertheless, if you do find yourself in need of a new gas boiler, check out our boiler buying guide for more help on choosing the right boiler for you.