boiler kettling: what it means and what you can do

Boiler Kettling | What it means and what you can do

Boiler kettling is a mix of whistling, popping and bubbling sounds that come from your old boiler while it’s in operation. It’s an alarming sound for any homeowner to hear, especially if your boiler is old and prone to any of the combi boiler problems that can occur, and can easily disturb anyone trying to relax in their home.

There are several reasons why a kettling sound is coming from your boiler. The three most common causes of boiler kettling are leaks, overheating and a buildup of limescale.

It can be a comforting sound for some – indication that a cup of tea will soon be ready. But if you’re hearing similar sounds come from your old boiler, you may have a problem on your hands.

Your boiler shouldn’t really be on your mind a lot of the time. It needs to work silently in the background to make sure your home is comfortably heated with access to hot water when you want it.


viessmann boiler working silently in your home

But what does boiler kettling mean? How does it start? And what happens if I don’t do anything about it? You’ll have to get answers for these questions to make sure your boiler is in the best possible condition.

If it isn’t an option, then your next course of action might be to replace your boiler entirely. While there may not be an immediate danger, boiler kettling will still need addressing.

Here you’ll find all the info on what boiler kettling means, and how you can prevent it from happening again.

Here we go!

What is boiler kettling?

Boiler kettling is a mix of unusual gurgling and popping sounds that come from your boiler while it’s running. Because the sound isn’t exactly normal, worry and panic are often the natural responses. The good news, however, is that there are ways you can counter this annoying sound.

boiler kettling water sounds

What’s causing the boiler kettling?

The three most common causes of boiler kettling are leaks, overheating and a buildup of limescale.


A leak in your system can be a reason for your boiler kettling. If you start to hear a whistling or gurgling sound, the first thing you should do is check for leaks.

leak causes boiler kettling

You may have to look quite hard – they can be in hard-to-spot areas close to your boiler. It could be there because of a poor quality installation you’ve had in the past, but you’ll want to find the leak as soon as possible.

How it’s solved:

Regardless of why the leaks are there, you’ll need a qualified engineer to identify where the leaks and to sort them out. If you try and do the heating system work yourself, there is a high chance that you’re breaching the terms of your warranty (we advise you to proceed carefully and maybe engage with a professional to ensure safety and efficient ratification for your problem


If your boiler keeps cutting out, kettling noises might not be the only reason – it could also be overheating. This occurs often for boilers that are reaching the end of their lifespan.

overheating causes boiler kettling

How it’s solved:

For tackling the issue of overheating, check through the manual for the boiler and thermostat. Boiler kettling isn’t something that should occur for any fully operational boiler. If it’s quite old, start looking into comparing prices or get a free, no-obligation quote online from us.



Limescale Buildup

boiler kettling causes limescale buildup

If your boiler is past its prime, there might be a build-up of limescale around the heat exchanger.

The now restricted flow of water will still continue to heat up here and because of the restricted space, the heat exchanger will become too hot and start to steam. The water inside the boiler then starts to boil, which is what causes the noise.

If you live in a hard water area but are looking to get a new boiler, you have 2 options – either purchase a full house water softener system, or ensure the installer installs at least a hard water filter.  This component will need to be changed every 3-5 years.

water hardness can help solve your radiator problem

Limescale naturally occurs because of the mineral content of the water. This largely depends on where the property is located, with varying levels of calcium and other minerals across the country.

If you do decide to purchase a new boiler instead, then be sure to choose one with a reliable heat exchanger. As an example, Viessmann uses Inox-Radial heat exchangers made out of stainless steel. With a material density close to surgical steel, their boilers are highly resistant to corrosion, lasting a lot longer than many other boilers on the market.


How to fix a kettling boiler

how to stop boiler kettling

Now for the interesting part!

If you’re able to determine the source of the boiler kettling, then solving the problem becomes a lot easier.

If it’s a mechanical issue such as gas burner pressure or a design flaw in the system, then you should call in a professional to come and sort it out.

However, if you’re able to eliminate a mechanical issue as the reason, then it’s most likely because of mineral deposits on the heat exchanger.

inox radial stainless steel heat exchanger

Inox-Radial stainless steel heat exchanger

To combat this problem, there are several things that you can do:

  • Chemical/Power/Advance flush the system – A similar response if your radiators are filled with magnetic sludge. Performing a flush on your system helps clear the build up of any rust or limescale that can restrict your water flow.
  • Add a liquid inhibitor to the system – This is a key part of any type of flush on your central heating system. In short, chemical inhibitors help prevent further corrosion and must be capable of protecting various materials including steel, copper, brass and aluminium.
  • Noise Reducer – This is often added to central heating systems that already have an inhibitor in ‘hard water’ areas where a build up of limescale forms. These chemicals work by slowly breaking down the limescale build up which can then help reduce the kettling noise coming from the boiler.
  • Use a Magnetic Filter – Magnetic filters are very useful devices that work to remove both magnetic and non-magnetic dirt particles from your central heating system. The Spirotrap MB3 Magnetic Filter is one of the best ones on the market today which we frequently include in our installations.

Can a boiler explode?

A boiler ‘exploding’ would be a little dramatic, but to prevent any long term damage after you hear kettling sounds, you should address the problem straight away.

can a boiler explode?

Manufacturers design their products with these kinds of outcomes in mind, implementing various safety responses to prevent further damage. However, the best response to any problem like boiler kettling is to seek professional advice and have someone with industry knowledge assess the situation.

Boiler breakdown?

If your boiler is over 10 years old, you may want to seriously consider a replacement as opposed to a repair.

If you’ve tried all the responses talked about above, or you’re looking to just start over with a replacement central heating system, then you needn’t go any further than Boilerhut. We can provide a free, no-obligation quote for you which breaks down your user profile and property type to determine which boiler is the best option.

We can also offer extended warranties on our installations, meaning you can feel reassured that you’re taken care of for at least the next decade.

If you’d like to know more about which type of boiler is best for you, please read some of the following articles:


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