A boiler is something many of us take for granted - when it works, it’s an appliance that we rarely have to think about. It comes on automatically, unlike our dishwashers or ovens, and provides us with heat when we need it. But on the odd occasion that it doesn’t ignite, you can be left in a cold home with no hot water. Finding the reason why it hasn’t turned on can be frustrating, too.

Why won’t my boiler ignite?

Below, you can find some of the reasons why your gas condensing boiler won’t ignite and some practical steps you can try before calling out a Gas Safe registered engineer.

No gas supply

Your boiler may not be the problem. Instead, it could be an issue with your gas provider. One of the first things you should check if your boiler hasn’t come on is whether your home still has a gas supply. You can do this by turning on a gas hob, oven or other gas appliance, such as a fire. If your gas hob or other appliance works fine, then you know that your home is still connected to the mains gas supply and this isn’t the problem. However, it’s always better to rule this out first.

A tripped fuse

Boilers require a small amount of electricity in order to ignite and so a tripped fuse could prevent your boiler from turning on. You should locate your home’s consumer unit and check that all of the fuses are on. In addition you may like to check the isolation switch next to the boiler to ensure this is switched on and the fuse is ok.

Alternatively, if there’s been a power cut overnight, this may have altered the boiler’s programme, resetting it or erasing the programme altogether. This means that if a fuse has been tripped or you lost power, the boiler might need reprogramming.

Your home is already at the right temperature

When you programme modern boilers, you can set the temperature that you want your home to be heated to. Before reaching the conclusion that your boiler isn’t working, it may be that your home has already reached the set temperature. For example, if you’ve set your boiler to heat your home to 21 ℃ but the thermostat is registering at 21.5 ℃, the boiler won’t turn on as your home is already above the temperature you’ve requested.

You can check that your boiler is still working by boosting the thermostat to 23 ℃ and waiting for the boiler to kick in. If it does, this solves your problem. However, if it doesn’t, you may need to dig a little deeper. 

Faulty gas valves

The gas valve controls the amount of gas that can flow into the boiler for burning. When more heat is needed, more gas is allowed in and the opposite occurs when your house has reached its set temperature. If this valve is blocked or damaged, the gas cannot enter the chamber and so your boiler won’t be able to ignite.

Alternatively, the burner might be blocked. When your boiler burns gas inefficiently it can produce a greater quantity of particulates which result in debris in the heat exchanger or burner .

These are not issues you’ll be able to check yourself - you’ll need to contact a Gas Safe registered engineer to look at your boiler and see if this is the problem. In most cases, the boiler will take a bit of cleaning and maintenance to clear the blockages and should be back up and running in no time.

Low pressure

Some boilers won’t ignite if the gas or water pressure is too low. Low gas pressure could be a problem with supply in the area and you may need to call out the supplier to check.

Alternatively, it may be that the water pressure is too low in a sealed system boiler. You will be able to see if this is the problem by checking the pressure gauge on the front of your boiler. This is a relatively easy fix, however a frequent drop in pressure could suggest that there is a leak in the system. If you’re finding that you have to repressurise your boiler often, this leak will need to be fixed, this work can be carried out by a qualified heating engineer.

What does ignition lockout mean on a boiler?

Some of the problems mentioned above could cause your boiler to go into ignition lockdown. This means that the boiler has turned itself off because of an issue, such as low water pressure, no gas supply or a lack of electricity. You’ll generally be able to decipher the problem as the boiler should show a fault code on the screen. You can check what this fault code means and how to get rid of it in the installation or manufacturers manual. Generally, the code will go away when you reset the boiler, however, the error will probably continue to reoccur until the problem is fixed. Therefore you should have the boiler looked at by a suitably qualified heating engineer.

How to ignite a gas boiler

If your boiler won’t turn on, there’s generally a good reason for this, and so trying to ignite the boiler yourself may be dangerous. In the past, you may have been able to ignite the pilot light yourself and get your boiler running again. However now, most boilers have an electronic ignition which does this automatically.

If your boiler isn’t turning on and you’ve tried the obvious things, such as checking the gas supply or resetting it, you should call a Gas Safe engineer to determine what the problem is. They will likely need to remove the boiler’s front cover to access the boiler controls, and you should never attempt to do this work yourself. 

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