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Why does my boiler fire up and then cut out?

Discover what is causing your boiler to fire up then cut off and how to fix this to stop costs escalating.

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Why does my boiler fire up and then cut out?

Your combi boiler firing up then cutting out is nothing to worry about. It is usually the result of its ‘preheat’ function. Basically, it's a way of ensuring that hot water is ready to be used in the taps throughout your home.

Although, when the boiler turns off after firing up more consistently, you are likely experiencing short cycling. This will eventually damage the unit itself as well as making your gas bills climb higher.

Find out why your boiler fires up then stops working and how to fix it in this dedicated guide.

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If your boiler is constantly firing up then cutting out, you may need to seek help from an engineer.

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Reasons your combi boiler fires up then cuts out

Causes of a combi boiler cutting out


Faulty Pump Boiler or pump overheating, strange noises from pump, heating taking too long to come on
Airlock Water not coming out of taps, heating not coming on
Blockage in the heating system Strange noises coming from the heating system, boiler overheating, radiators not heating properly
Frozen condensate pipe Lack of external pipe insulation, extended period of cold weather, strange noise from boiler
Insufficient fuel supply If you have a pay meter it may need to be topped up. Lack of fuel if LPG, oil or biofuel
Low water pressure Pressure gauge is below 1 bar


Faulty Pump

Your water pump should be in excellent working condition for your central heating system to be efficient. A faulty pump means that water isn’t being pumped around effectively. Over time debris build up could caused a blockage within the pump, a problem that is most common in older systems.

A hot flush of the pump will need to be carried out by a Gas Safe engineer to rectify the problem. If the fault has caused irreparable damage to the pump, then a replacement (priced at around £300) may be necessary.


Airlocks are the result of air being trapped in the hot water within the central heating system, which then creates a blockage and prevents it from circulating.

There are a number of ways to clear airlocks before the need to call out an engineer. You can find out how to remove airlocks in pipes.

Blockage in the heating system

Another reason for your combi boiler firing up then cutting out is a blockage in the system.

As heating systems get older, they collect sizeable quantities of debris such as limescale, rust and sludge, which can eventually form a blockage.

In addition to causing your combi boiler to cut out soon after firing up, a blockage in the central heating system can reduce the efficiency and life expectancy of the unit. To prevent a build-up, it's highly recommended to have a magnetic filter installed.

If you find that you already have a blockage, then you’ll need the assistance of a Gas Safe engineer to carry out a chemical flush on your system. Once the system is cleaned, then the magnetic filter should be fitted.

Frozen condensate pipe

Finding that your boiler turns off after a few minutes could be due a frozen condensate pipe. Water in your condensate pipe can often freeze in the colder months, thus causing a blockage. This will prevent waste water from being disposed of, which will lead to your combi boiler cutting out.

After locating your condensate pipe (check out your manual if you’re unsure) you can thaw it safely at home if you find it to be frozen. 

Read our full guide on thawing a frozen condensate pipe.

Problems with your fuel supply

Anything that gets in the way of your combi boiler receiving continuous fuel, will cause the unit to cut out. To see if you are having issues with your fuel supply check that all other gas appliances in your home are still working effectively before getting in touch with your energy supplier.

If you have a pay meter then make sure this is topped up, and if you operate your heating with an alternative fuel, such as oil, LPG or biofuels such as wood pellets, you should ensure that it is in good supply.

Incorrect Boiler pressure

Your boiler pressure being correct is vital to keep your unit working effectively; it should sit at around 1.5 bar for optimum efficiency. Make sure it is at the correct level, by taking a reading then fixing the boiler pressure.

If it is too low, you might be suffering from a boiler leak which could cause your system to turn off as a safety measure. Visually inspect all elements of the central heating system (pipes, radiators and boiler itself) for a leak. If you do uncover one, you should contact an engineer for a repair.

What are the boiler error codes to look for?

To help you work out exactly why your boiler turns off after a few minutes, you should see an error code displayed on the front display.

If you have your user manual to hand you can look up what these codes refer to, which will give you a better idea of how to handle the problem.

If you can’t find it, we have error code page for a number of manufacturers in our advice centre, where you can also diagnose a range of heating issues.

Vaillant boiler fault codes

Baxi boiler fault codes

Ideal boiler fault codes

Worcester Bosch boiler fault codes

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