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Boiler Not Firing Up? Main Failure Causes & How To Fix

Boiler not firing up? Here is our guide to reasons why and how to fix it

You’ve just arrived home on a cold winter evening, and you’re looking forward to getting into your warm home and taking a long bath. So, if you walk into a freezing cold house with no hot water, getting the boiler up and running as soon as possible will be your top priority.

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However, if you try to get your boiler working but it still does not fire up, we have some assistance and advice for you.

gas safe register

Fortunately, there are some boiler problems that you can check for, which could mean that the boiler is back up and running in no time. And if they don’t work, there are some really simple DIY solutions you can try before reaching for the hot water bottle!

If you do need to call an engineer, keep in mind that they must be a Gas Safe registered engineer in order to work on a gas appliance. They should service your boiler, such as Glow Worm boiler service, to see what the issue is with your boiler.

However, if your boiler is not working you should read this article.

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First things to check

As a result, it is not always the boiler that is the source of the problem. These are the first things to look into to see if you can get your home nice and warm quickly.

Thermostat configuration


If your boiler thermostat is set to a low temperature, it’s possible that even though it feels cold, it’s not yet cold enough to turn on the heating. It’s very easy to knock the dial or accidentally lower the minimum temperature, so check that first.


The boiler timer should be checked next. Have you ever set the heating to come on later than you intended? Perhaps you changed it last week when you knew you’d be home later and then forgot to change it back.

If the timer is set to turn on when you get home, that will be the cause of the icy reception. Another cause of timer malfunctions is a power outage. This can cause the timing to become out of sync.

Gas supply

Is the gas supply operational? Try other gas appliances, such as a gas cooker, to see if they are working properly. If your gas appliances are limited to the boiler, check with a neighbour to see if their gas supply is working properly.

The gas pressure in your home can occasionally cause issues. If the gas pressure is low in the boiler, the flow may not be sufficient to ignite the boiler.

If there appears to be a problem with the gas supply, such as no supply or low gas pressure, you should contact your gas supplier or the Gas Emergency Service at 0800 111 999.

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Carbon monoxide

While we’re talking about the gas supply, if your boiler is lighting, but there’s an orange or yellow pilot light, then it could be producing carbon monoxide. This is one of the harmful gases that can be fatal.

If the pilot light on your boiler is anything other than a crisp blue, you should turn the boiler off and call a gas engineer to come out and inspect it for you.

Electricity supply

Even a gas boiler needs some electricity to ignite. It doesn’t need much, but if there’s no power supply to your boiler, then it’s not going to turn on and that’s going to mean a lack of heating and hot water.

Fuse box

Next up is to check the fuse box. If there have been problems with the electricity supply then you might find that the fuse to the boiler needs resetting.

Prepayment gas meter

If you have a prepayment gas meter then do have a quick check to make sure that you have enough credit for the boiler to fire up.

Error codes

Although boilers are pretty straightforward there are a number of different problems that can occur. So most systems have a boiler display on which a fault code is shown. Then, when the boiler isn’t working in the way it should you’re provided with information on what the issue is.

Now, do bear in mind that each boiler brand uses different codes, so that means that Baxi boiler error codes for a pressure issue will be different from the error codes for Worcester Bosch boilers. There can also be some variations between the different models, even from the same manufacturer.

If you have your boiler handbook to hand that will list all the error codes along with their meaning. If you’re not sure where the handbook is, you’ll be able to download another copy from the website for your boiler brand.

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Things to try

So, you’ve tried and checked all of our first lists, now we’re moving on to more simple diagnostic checks that might help you to get the heating system up and working.

Resetting the boiler

If the electricity supply has gone off during the day, it can sometimes cause a boiler lockout situation. Not until the boiler is unlocked will it start to function properly.

boiler pressure

This is another situation where you need to check the error code being displayed on the control panel. This will confirm that the boiler is locked out, and then your manual will give step by step instructions on how to unlock the boiler.

Check the pressure gauge

Your boiler needs a delicate balance of air and water for it to function correctly. The boiler pressure relates to the pressure of the hot water that’s flowing through your heating system.

The ideal pressure for your boiler is 1.5 bar but your system is likely to operate just fine with a pressure of between 1 and 2 bar. The pressure gauge on the front of the boiler will give you a reading of what the pressure is right now.

Low pressure

If there is low pressure then the boiler will fail to ignite. While high pressure, so anything over 2 bar, may result in a lockdown situation.

boiler pressure meter

It is normal for boiler pressure to fluctuate a little and for it to decrease over time. But, if there is a sudden drop in pressure then that’s going to need further investigation by a heating engineer as it may be due to a fault with a pressure valve.

High pressure

If the boiler pressure is too high, then some of the radiators within your central heating system may need bleeding.

Bleed the radiators

To reduce the pressure in the heating system will need you to bleed all the radiators. This lets excess trapped air escape and rebalances the air and water in the system.

For this, you’re going to need the radiator key, a cloth, and a small container to collect any water that leaks out.

1. With cold radiators, place the cloth below the radiator bleed valve to catch any leaking water

2. Then use the key to open the valve, which in turn releases the air trapped in the radiator

3. Close the valve back up

4. Now recheck the water pressure meter on the front of the boiler

5. If you’re in the green then fingers crossed that the boiler will come to life.

Frozen condensate pipe

frozen pipes

The condensate pipe travels from the boiler to an external drain to remove excess liquid from the boiler. If there has been very cold weather then the wastewater can freeze causing frozen pipes and a blockage. Because the boiler can no longer get rid of the waste then it goes into lockdown.

This is another issue that’s easy to fix without needing the help of a boiler engineer. All you need to do is to pour warm water over the external condensate pipe to thaw the blockage and then reset your boiler.

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Issues with the central heating system and boiler

hot water

So you’ve done all the checks but you’re still having problems with the boiler not firing up meaning no central heating or hot water.

Now we get to the list of problems that are going to need the assistance of a gas-safe registered engineer. Do remember that UK legislation is in place to prevent anyone who is not a gas-safe engineer from removing the casing of a gas boiler.

Gas is a very safe energy source when it’s maintained by a professional and qualified engineer. If you have a relatively new boiler then you might still have warranty cover in place. For older boilers, a boiler cover plan can be a great option to avoid big and unexpected repair bills.

No pilot light

The boiler pilot light is the flame inside of the boiler that catches with the gas which then enables the water to be heated. If there’s no pilot light then the boiler is not firing to then enable the heating process.

One of the common reasons for there being no pilot light is that the pilot light jet has become covered in debris. The blocked burner is then unable to light up.

pilot light

In older boilers, you can usually see the light of the flame through a small window in the boiler casing. On newer models, there will be an error code displayed to let you know that there’s a pilot light problem.

Burner replacements are a quick and easy job for your gas safe registered engineer to fix so you should have central heating and hot water back up and running in no time.

Faulty burner

When the burner is working it produces CO2 as waste gas. Over time this then causes the burner to become clogged up and develop mechanical faults. As a result, the burner might sometimes work and other times refuse to ignite, causing an ignition fault.

The burner within your boiler does age over time and with wear and tear replacing it might be the best option.

Low gas pressure

In some cases the supply of gas to the home is normal but the boiler is not firing because the gas valve is preventing enough gas from getting into the system.

When this happens, the boiler will go into lockout mode and then display a fault code. This is when you then need to get in touch with a gas-safe registered engineer who can test the pressure of the gas and work out why there’s not enough reaching the boiler.

Two causes of this problem are a gas meter that’s become frozen and a faulty gas valve.

1. Faulty gas valve

gas valve engineer

This is a more common cause of the problem as the gas valve controls the amount of gas that is able to flow into the boiler. It opens and closes which lets in more fuel or less depending on whether you need more heat or less.

The valve may have become damaged or blocked or it may just need adjusting to allow more gas to flow through. It’s also possible that a fault in the wiring to the valve can cause problems with it functioning correctly.

2. A frozen gas meter

If the weather has been very cold then it is possible that the gas meter becomes frozen. Ensuring that the meter is lagged will prevent any future issues.

Electrode and ignition lead faults

If you can hear clicking noises when your boiler is trying to ignite then it could be that it’s the electrode and ignition lead that could be causing the problem.

More often than not, gas-related issues result in intermittent operation, so the boiler ignites for a second and then goes off again. If it is a problem with the ignition lead and electrode, then the boiler won’t be able to ignite at all.

A heating engineer will be able to use a multimeter to check out the electrode and ignition lead and confirm if that’s the problem behind the lack of central heating and hot water.

Faulty thermocouple

The thermocouple is a safety device that turns off the gas supply when the pilot light goes off. Its heat sensor is connected to a solenoid and when the sensor is not heated by the boiler’s flame, then the solenoid closes the gas supply.

When a thermocouple becomes faulty, it prevents the flame from staying alight. Generally, a boiler thermocouple that has burned out or is no longer operating correctly, can be replaced relatively easily by a heating engineer.

Boiler lifespan

Although we have shown you the many ways to fix your boiler if it is not firing, sometimes your boiler may just be past its lifespan. If it has any of these issues then they can likely be fixed, but fixing these may just prolong the inevitable of having a broken boiler. Most modern-day boilers last around 10-15 years, so if yours is around this age and continuously has issues, it may be time to get a new boiler.

Time for a new boiler?

new boiler

When it feels as if you can no longer rely on your heating system, then the time may have come to start thinking about a new boiler installation. No longer will you need to dread the latest boiler repair bill or astronomic energy bills from your inefficient system.

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Getting a new boiler quote is a great way of seeing recommendations for systems to meet your heating needs. And with boiler installations available within a few days of placing the order, your home could soon be ready for whatever the British weather can throw at it!

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