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Boiler Kettling – What’s That and How Can You Stop it

An image of boiler making a kettling noise

If you think something weird is happening with your boiler or you’re hearing strange and uncommon sounds coming out of it, the reason could be what we call boiler kettling

We’ve prepared this post for people who have heard a kettling-like noise in their operational appliance, people who experience issues with their boiler system and DIY enthusiasts who want to fix their kettling boiler on their own. We give more details about the problem and what it means for your unit. We’ve listed several common causes and a few tips on how to stop it.

What is a Kettling Boiler?

Don’t worry if you’ve never heard this term before or aren’t sure what it means, we’re here to explain it to you. A boiler is making a noise like a kettle, or either/or a mix of whistling, popping, rumbling and bubbling, usually heard while your appliance is working. This happens when something inside of the boiler is interfering and slowing down the flow of processes. Water in the boiler shouldn’t reach 100 degrees Celsius and shouldn’t boil, as if this happens, and the water boils, you start hearing the sounds we’ve listed above.

Every boiler produces some noise while working, but it should be quite low and hard to pick up on. While these sounds are normal, catching on louder kettling noises produced by your boiler is something to worry about.

Is it dangerous?

Most, if not all, modern boilers have built-in safeguards which are supposed to detect overheating and turn off the system as a preventative measure even before it starts kettling. 

If you have an old boiler that makes strange noises, better turn it off. If it reaches the stage of kettling, it has the potential to be dangerous,  since theoretically, the high internal pressure could cause the internal pipes to burst, leading to steam emissions and even electrical hazards.

Why is Your Boiler Kettling?

There are several reasons why your boiler makes kettling sounds. Some are simpler to fix than others, but no matter which of the following is the cause, you need to deal with it right away. You should find a trusted company for emergency boiler repair in London as soon as possible.

1. A leak in your boiler system

One of the common problems causing your boiler to produce a whistling sound is a central heating system leak. You have to look carefully to find out where the boiler leak is, as it can be in any part of your system, including hard-to-spot places. Also, don’t forget to investigate the pipework and the radiators throughout your home.  

There are various reasons for a boiler leak. The most common are poorly installed pipework, corrosion that usually comes with older units, over-pressurisation and others.

2. Your system is overheating

If there are no leaks, the reason for kettling sounds may be boiler overheating. This could be because of a wrong thermostat setting or, overall, a malfunctioning thermostat. Whichever the reason, the water inside of your boiler is getting hot enough to turn into steam and that’s what makes the strange sound.

3. Limescale and sludge build-up

Limescale build-up is the third common reason for your boiler to make weird sounds. The accumulation of limescale and ‘sludge’ anywhere in the heating system is a problem that can cause various issues to the appliance and the pipework. Also, often that’s the reason why your radiators have cold spots. 

So, limescale build-up in pipes close to the boiler can also make it produce gurgling sounds because it obstructs the flow of water.  A water softener installation will prevent scaling and preempt preventable damages.

4. A faulty thermostat

Having an old system? Then probably your boiler thermostat is not working the right way. After some time, it’s often the case that the thermostat or the diverter valve wore out, and in such a case, a specialist must replace the damaged part. Keep in mind that if your boiler is an antique, it may be more cost-efficient to buy a new energy-saving boiler than spending money on costly repairs.

If the thermostat and boiler are not communicating, you need to get your appliance inspected by a Gas Safe Engineer. Get one off or annual boiler service and the team will adjust the settings or change the whole regulator if needed.

5. Issues with your boiler pump

The central heating pump, usually found near the boiler itself, could be damaged. It works by pressurising the water and pumping it back to your system, and sometimes, the process doesn’t go as planned. A faulty boiler pump may not be pushing the water quickly enough through the heat exchanger, which causes it to make weird sounds. 

How to Stop Kettling in a Boiler

We can give you some pointers on how to fix a kettling boiler if you feel confident with your knowledge and experience. Please keep in mind that most of the following procedures are not for newbies, and if you’re uncertain of your skills, definitely hire a professional boiler engineer to fix your heating system safely. Also, repairs concerning the boiler itself, and not the external parts must be done only by Gas Safe plumbers.

Furthermore, if your boiler is new, working on the problem yourself as an unlicensed professional, you are most likely to void the warranty.

But here are several boiler kettling fixes you can check out:

Internal or external leak repair

You should get a qualified engineer to fix a boiler leak because they’ll most likely need to replace the pipe or mend it the right way. Attempting DIY methods such as glueing or wrapping the pipes with something to seal the leak is never the answer, as you can even cause bigger issues. Better pay the boiler leak repair cost once and have peace of mind that your heating system will continue to work smoothly. 

Heat exchanger maintenance

A simple solution to the problem with a kettling boiler can be to clean the heat exchanger if it’s the thing that’s causing the problem. Locate it, take it out and scrub it with a soft brush if it isn’t very filthy. However, if there is too much limescale build-up and cleaning it is impossible, then a heat exchanger replacement is the best solution. 

For the future, you should make it a task to maintain your heat exchanger and boiler regularly. For some maintenance tasks, a professional is needed, but there are also several things you can do to maintain the good condition of your boiler

Replace your thermostat

If you’ve discovered that the problem is with the thermostat, then based on the exact situation you’ll probably need a replacement. If you’re uncertain what the problem with the regulator is, a trusted engineer will determine whether the settings are wrong, or it’s simply broken. 

Perform a power flush

A central heating power flush service can solve your problem with limescale and sludge build-up from the system. This is basically a deep, powerful cleaning of the insides of your heating system. 

How to power flush a heating system? This job is usually done by a professional with special equipment and it’s not a DIY job. A powerful external pump is used to power-flush a combination of chemical substances throughout the central heating system to eliminate the sludge build-up.

Install a magnetic filter

A boiler magnetic filter is a device that removes magnetic and non-magnetic dirt particles from the insides of your heating system. You can use the filter as long-term protection as it collects sludge and debris while water flows through your system and doesn’t allow troublesome build-ups to occur.

Get an electrolytic scale inhibitor

A brilliant solution for your limescale buildup issues. The inhibitor acts as a water filter and alters the lime scale’s makeup, preventing it from sticking and building up inside the system. Best of all, it’s a low-cost maintenance-free device that keeps the water’s easy flow through your entire system.

Use an all liquid inhibitor

This is a strong liquid that breaks down the rust and minerals in the water quickly and efficiently. Using a liquid inhibitor regularly prevents many problems from occurring inside of your heating system, as the product destroys any build-up and is even recommended by boiler manufacturers. In fact, not using such a product for regular internal cleaning may void the boiler’s warranty.


If your boiler is about 10 years old or older, you should consider replacing it entirely. New, more modern boilers are energy efficient and easier to set up, plus they offer a range of additional features. 

We do not recommend that you try any of the above-listed fixes by yourself if you lack experience and Gas Safe Register certification. As we mentioned, kettling isn’t that dangerous, but it’s better to leave it to skilled and trained boiler engineers

Boiler Kettling – What’s That and How Can You Stop it

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