Why Does My Boiler Keep Turning Off Re April 24, 2020

Why Does My Boiler Keep Turning Off

Boiler turning off

Why does my boiler keep turning off? It’s likely a recurring boiler fault which we’ll diagnose in this article. There may be a simple solution to fix boiler faults.

A boiler is not like a computer, and you can’t fix 99% of problems by turning it off and back on again. If you start up your boiler and it turns itself off again, then you’ve come to the right article. We’re going to look at possible causes of why your boiler keeps turning off and how to get it fixed.

There are a few potential causes that could lead to your boiler cutting out, from overheating to low pressure. Some issues you may be able to rectify yourself and others will require a Gas Safe engineer to look at.

If you have a combi boiler and it turns itself off every now and then, it’s probably the boilers ‘pre-heat’ function. This is perfectly normal and doesn’t indicate a fault with your boiler, your boiler is just turning itself on to pre-heat water so that it’s ready on demand when you need it. 

If your boiler is turning itself off and on again every few minutes then we are looking at a potential issue called ‘short-cycling’. Not to be confused with cycling shorts, which are comfortable and practical, short-cycling is bad for your boiler and bad for you as it will increase your heating bills.

Short-cycling boiler fault

Within your boiler, a small reservoir of water is kept heated within your heat exchanger so that your boiler can provide you with hot water on demand. When this water starts to cool, the boiler’s internal thermostat will trigger at a certain temperature and reheat the water. It will then switch itself off again once the water has heated.

Your boiler will keep repeating this process when the water temperature drops, this will mean your boiler is using fuel and your heat exchanger is being overworked. This will waste money on fuel bills, increase carbon emissions and decrease the lifespan of your heat exchanger.  
A cracked heat exchanger is one of the more expensive issues that can go wrong on your boiler, costing between £350-£550 (depending on the boiler model) just for the part alone. So it’s something you don’t want to overwork.

What causes short-cycling?

Having an oversized boiler is the main cause of short-cycling. This means the boiler you have in your home is more powerful than you need it to be. It will produce more steam than it can condense, causing short-cycling and your boiler to lockout.

In days gone by, heating engineers would often advise on oversizing boilers as older boilers were much less efficient and would experience up to 30% losses in fuel efficiency.

Modern combi boilers are over 90% efficient, so there is no need to oversize your boiler. When you take the WarmZilla survey, we will calculate the correct boiler size to suit your home, we have even saved our customers money by recommending a lower kW boiler than they had been recommended previously.

Valve issue

If there is an issue with your temperature control valve or TCV as they’re known, it means that the water temperature in your boiler is no longer regulated. If the temperature gets too high it can cause leaks within your system. This will cause your boiler to shut off to protect itself from overheating.

Another valve issue can occur if you have a closed valve stopping the water flow through your boiler, check the valves underneath the boiler are set to open, if they are then it could be a valve located inside the boiler which you won’t be able to fix.

You will need to call a Gas Safe engineer out to look at the problem. Any issue involving taking the cover off your boiler needs to be fixed by a Gas Safe registered heating engineer.

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Water pressure

Your boiler likes a nice steady 1.5bar on the pressure gauge located on the front of your boiler. Too little pressure or too much pressure and they’ll turn off and display an error code that will mean nothing to you, unless you’re a boiler whisperer, like us.

Low pressure can be caused by a leak in your system. This could be from a radiator, a pipe joint or from underneath your boiler. If you have a leak in your system it’s a matter of time until your boiler turns itself off. Fix the leak, repressurise your boiler and you’re back up and running.

If there is air trapped in your system, try bleeding your radiators, trapped air can stop the water flow in your system, which will cause your boiler to shut down.

We’ve written an in-depth article about boiler pressure, too much, too little, how to decrease or increase pressure – and how to repressurise your boiler.

Heat exchanger boiler fault

If your heat exchanger has gone and your boiler is over 7 years old we would recommend replacing your boiler. A heat exchanger is one of the most expensive parts to go wrong and the cost of installing a new one is often not worth it to keep an older boiler going.

Check our best boilers of 2021 article. We know it’s boring doing research on a new boiler so we’ve put our years of experience to use by making it easier for you to choose a reliable and efficient boiler.


Your thermostat monitors the external temperature and turns itself on if the temperature drops below a certain level (set by you). If there is a fault with your thermostat then it can’t accurately measure the temperature and it will come on when you least expect it. This can cause your boiler to turn off and on again unexpectedly. 

If you have an older thermostat, then upgrading to a wireless or smart thermostat can help you save money on your heating bills by giving you more control of temperature. 

Some learning thermostats such as the Google Nest, learn your habits – when you’re at home, when you’re out, what rooms you use, what rooms you don’t. It adjusts the heating accordingly to save you money.

Every WarmZilla boiler comes with a smart thermostat included in your order to make sure your heating system is as efficient as it can be.


Water pump boiler fault

If you have a malfunctioning water pump then water is not being moved around your system as it should be, this will cause your boiler to turn itself off to protect itself from overheating.

If you have an issue with your water pump you will need to call out a Gas Safe engineer as this is not a job you can fix yourself.

Fuel supply

Interruptions to your fuel supply will also cause your boiler to keep turning off. Check other gas supplied appliances to make sure they are still functioning or whatever fuel source your boiler runs on.

If you are on a prepaid meter then make sure you have credit, sounds silly but you’d be surprised.

If you are experiencing interruptions to your fuel supply then contact your energy supplier and get them to check for issues with supply.

Frozen condensate

A condensate pipe is essentially a small waste pipe that carries acidic water safely away into a drain from your boiler. 

Water in the condensate pipe can freeze when exposed to very cold temperatures. When this occurs, the boiler will continue to dispose of this waste water but as it now has nowhere to go due to the water freezing and essentially blocking the route to the drain, it backs up into the boiler.

Your boiler will then lock itself out to prevent any damage and will let you know via a fault code or a sequence of fault lights, depending on what boiler you have. Another giveaway of a blocked condensate pipe is you might be able to hear a gurgling noise inside the boiler.

Unfreeze the pipe using warm water and reset your boiler. This is a common issue in colder months and is one of the easiest fixes out there.


It is a frustrating issue if your boiler keeps going into lockout to protect itself, but it does this for a reason and the underlying issue needs to be dealt with.

When a boiler locks out it will display an error code on the display, this will help you to narrow down what the issue may be. Hopefully it will be something simple like trapped air in your system that can be released by bleeding your radiators or a small leak from a radiator valve or accessible pipework but often the problem is a bit more complicated.

We hope this guide has given you some ideas of what to look at if you are experiencing issues with your boiler turning itself off. If you have any questions please feel free to use our live chat and you will speak to a Gas Safe registered engineer who will be more than happy to help.

On the other hand, if you feel that your boiler may just be coming to the end of its lifespan, then why not try our new Boiler Comparison tool which lets you compare your current boiler with other boiler models and brands, or you can compare up to three boilers at once, helping you find the best new boiler for your home. 

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