Why is my boiler making a strange noise? Re October 12, 2020

Why is my boiler making a strange noise?

Ariston Boiler

Boilers are great when they are working well but when something goes wrong you realise just how important they are. If your boiler has started making strange noises then you’re probably starting to worry about how much it will cost to put it right again.

Whether your boiler is making a whistling, banging, humming, vibrating, clicking, gurgling, booming noise; or if it sounds like an aeroplane taking off, a kettle boiling, or the BeeGees – we will try to explain what might be causing your boiler to make these noises and give you an idea of how much it might cost to get it fixed.

Combi boilers tend to last between 7 – 15 years depending on the brand, whether it’s been serviced regularly and luck of the draw. If you’ve had your boiler for a while, it’s out of warranty or it’s had a few issues and you think it might be time to stop sinking money into it – why not get a new boiler quote from WarmZilla?

Answer some simple questions about your home and we’ll give you a selection of boilers to suit your needs. No sign-up required, just an instant, fixed-price quote on a new boiler. Prices start from as little as £1489 for a Vokera boiler or £1649 for a Worcester Bosch boiler, with the option to spread your payments via boiler finance, from just £9.80 per month. The information in this article is for more information purposes only, only a Gas Safe engineer is legally qualified to work on your boiler.

If buying a new boiler sounds like the best option, why not try out our Boiler Comparison tool which allows you to compare up to three boiler models or brands at once to help you find the perfect new boiler for you before you make your purchase! 

However, if you think your boiler still has a few more years left in it yet, then let’s get that strange noise diagnosed and sorted.

Banging or whistling boiler noises

If your boiler is making banging, whistling, popping, or gurgling noises; then the likelihood is that your boiler is ‘kettling’. It’s called kettling because it sounds like a kettle boiling, and it’s much the same process.

Kettling isn’t a process of retraining for your boiler because it fancies a career change, kettling is caused by a build-up of limescale or sludge on your boiler’s heat exchanger. This build-up restricts the flow of water in the heat exchanger, overheating the water, causing a noise like that of a boiling kettle to occur.

Kettling is more likely to occur in older boilers with cast iron heat exchangers, particularly in areas with hard water. Limescale build-up can occur in your pipework too, causing a knocking sound.

Another potential cause could be a faulty thermostat within your boiler sending the wrong signal about the water temperature and causing it to be over-heated.


You can try introducing some central heating inhibitor to your system to get rid of any recent limescale, however, older limescale will be harder to remove. Inhibitor can be bought from Amazon, hardware stores like B&Q or Screwfix for less than £15.

After you’ve added inhibitor to the system you can get a scale reducer fitted. This will catch any limescale going forward but if the issue is already quite established then you may need to call a Gas Safe engineer. Scale reducers range from £20 – £100.

It’s hard to put a price to solve kettling as it depends on how much limescale is present and whether it has damaged any of your boiler’s components. You’ll need to get a Gas Safe engineer out to take a look and assess the problem.


boiler being serviced

Tapping boiler noises

If your boiler or pipes are making a tapping noise then it’s likely to be caused by kettling. You’re more likely to experience a tapping noise when you first turn your boiler on.

Kettling is caused by a build-up of limescale in your system preventing the natural flow of water as it is pumped around your central heating system.

Kettling resulting in a tapping noise is more likely to be located in your system’s pipes or radiators. If the sound is more like clicking then it could be the sound of air bubbles trapped in the water in your system expanding and collapsing.

Another cause of a tapping noise in your system could be bits of central heating sludge (a mixture of metallic elements and rust from the metalwork in your system) that have broken off and are brushing against the sides of pipes and radiators as they get pumped around your system.


Sludge is easier to remove than limescale so you may be able to solve it by adding inhibitor to your system, to break down the sludge.

After adding inhibitor, we recommend giving your system a flush to get rid of any sludge (hot flush for older systems that could potentially leak, a stronger powerflush for newer systems).

A Gas Safe engineer will be able to complete a powerflush for around £400 and it will take around 4 hours to complete.

Knocking noises

Knocking noises could be caused by an airlock in your boiler pump. If the knocking noise is related to the pump then it will be more likely to occur when your boiler is first turned on or when running hot water.

If the knocking noise is coming from your pipework rather than the boiler, try to locate the area it’s coming from and check that the pipework is safely clipped. It may have worked loose from its clip or it may not have been secured properly to begin with, causing the pipe to knock against other pipes or floor joists.


Decent pump manufacturers will include a bleed screw which you can turn to release the air from it.

If the knocking noise is coming from your central heating pipes then try to identify where and secure them if possible.

Gurgling boiler noises

If you are experiencing gurgling noises coming from your pipework or boiler, it could be that you have air trapped in your system.

Luckily, this is one you can fix yourself with a radiator bleed key and a cloth.

Another issue that can result in gurgling noises coming from your boiler is a frozen condensate pipe causing water to back up into your boiler. We’ve covered frozen condensate pipes and how to fix them in a previous article.

To release trapped air all you have to do is bleed your radiators by following these steps:

  1. Switch off your boiler and let it cool completely
  2. Find the filling loop (flexible silver cable) and make sure both ends are tight or you may have an internal filling key but it’s the same principle.
  3. Open bath valves or turn your internal filling key to allow cold water into the system, this will repressurise the system.
  4. When the gauge reaches 1.5 bar close both valves.
  5. Remove the filling loop if it isn’t a permanent attachment.
  6. Turn the boiler back on.
  7. Check in a few days to see if it has lost pressure again.

If your boiler continuously loses pressure then there is a good chance you have a leak in your system which will need to be identified and fixed.

Vibrating or humming boiler noises

Vibrating, buzzing or humming boiler noises coming from your boiler could indicate that there is an issue with your boiler pump and a part on it has seized up.

If you put your hand on the pump (carefully) it should be warm to the touch but not hot. If it is hot, then there is likely an issue with an internal part.

If you have an electric water heater then the humming noise might relate to a heating element in need of tightening. This is a simple job you can fix yourself.

Another issue that can create a humming noise is if the bearings within your boiler fan are on the way out.

A faulty pump can also produce a grinding noise from your boiler. Most of the worst boiler noises are caused by a faulty pump.


If you tap the pump gently you may be able to free up the seized part. This is a temporary fix and you will need to get a Gas Safe engineer to identify the issue (probably limescale or sludge build-up within the pump).

A new pump fitted by a Gas Safe engineer will likely cost around £200.

Aeroplane boiler noise

One of the more alarming boiler noises is when it starts making a sound like an aeroplane or like a drone strike has just been ordered on your home.

This sounds like the end for your boiler but in most cases, it’s regarding an issue with your boiler pump. You’d likely pay around £200 for the new pump and labour costs to install it.

If your boiler is getting on then you may be better off putting this money toward a new boiler from WarmZilla rather than sinking money into a failing boiler.

We recommend getting any issues on your boiler sorted ASAP as the strain from one malfunctioning part can cause other parts to start malfunctioning.

Hissing boiler noise

If your boiler is making hissing noises; then your boiler is probably kettling. This can cause the boiler to overheat. There are many reasons for kettling, one is an increase in limescale inside the tank. Limescale can result from having water with excess calcium and magnesium in it that can build up over time.

Alternatively, the hissing noise could be related to trapped air in the system.


If the hissing is related to kettling (which is probably the case), we advise calling a Gas Safe engineer. The engineer will complete a powerflush for around £400 and it will take around 4 hours to complete. But if the hissing is not coming from the boiler but in fact is coming from a faulty flue or gas appliance, they’ll sort that out for you for a fraction of the price. 

If the hissing is because of trapped air, just bleed your radiator and adjust the boiler pressure. You can do that yourself without the need for a call out. 

If you live in an area with hard water, you could invest in a filter and an anti-limescale solution to prevent this from happening.

Whooshing boiler noise

Whooshing noises from your boiler can be quite alarming, it can also cause your boiler to vibrate. Whilst this sounds like a major issue it can be down to something quite simple.

Check your air intake pipe/flue for any blockages. This pipe comes from the back of your boiler and terminates outside your home. Check there is nothing blocking the pipe and remove it if there is. You should be able to feel air movement if you lightly place your hand over the pipe.

If there is no issue with your flue then it could be a blockage with your air filter. Some filters are accessible to you and others are located within the boiler, so you will need a Gas Safe engineer to take a look for you.

If you can access the filter then just remove it and vacuum or brush off any dust/debris and replace it.

Hopefully, this article will have helped you identify what the issue is with your boiler that is causing it to make a funny noise. If your boiler is making a noise not mentioned in this article then please let us know and we’ll add it in.

You can always speak to a Gas Safe engineer on our website live chat if you have any questions about your current boiler and any boiler issues you might be experiencing.

  • November 12, 2022, 8:07 pm

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  • November 15, 2022, 8:53 am

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