The smarter way to replace your boiler

  • Get FREE Quotes today
  • Compare quotes & save money
  • Over 5,000 engineers across the UK
Tell us about your job
Get Free Quotes

Boiler Not Igniting: 8 Possible Reasons Why and How to Fix It

Is your boiler refusing to ignite? We help you establish whether you can fix it yourself or you need to call in a heating engineer.

A gas boiler that won’t ignite is enough to ruin your day because it means you will be without heating and hot water until you figure out what’s causing the problem and fix it. If you’re struggling to get your boiler to ignite, you’ll be pleased to know that there are some simple checks you make yourself before calling a professional.

So, let’s not hang about. Here are the possible reasons why your boiler is not igniting and whether it needs a simple DIY fix or the expert eye of a Gas Safe registered heating engineer.

Top potential causes of a boiler ignition failure

Below, you can find out the most common causes of a gas boiler failing to ignite and how to fix it.

1. Tripped fuse box

Although you may think you’re boiler is a pain in the neck for not firing up, your boiler might not be the problem at all. It could be that your boiler works fine, but your fuse box has a tripped switch.

Check your fuse box to see whether one of the switches is pointing down. If you find a tripped switch, flick it back up to get your boiler back up and running again.

2. Blocked burner

Boilers produce carbon when they burn gas, and the gas can clog up in the burner and prevent them from igniting. Sadly, this isn’t an issue you can put right yourself, so you need to call in a Gas Safe registered engineer to clean up the carbon build-up.

Your engineer will likely suggest replacing the burner if there is any damage. Replacing the burner won’t be cheap. But it will be less expensive than replacing your boiler. That said, you may want to think about replacing your boiler if the one you have is old and out of warranty or keeps breaking down.

3. Trapped air in your radiators

If you’ve noticed lately that the top part of your radiators isn’t heating up as they once were, chances are air is trapped in your central heating system. Your radiators can develop a nasty habit of collecting pockets of air that rise to the top, which can result in your boiler not igniting.

The good news is that you can bleed your radiators to remove the trapped air in your central heating system. You can do this yourself or, if you prefer, leave it to a professional.   

4. A fault with the fan

Your boiler’s fan starts operating whenever you use your central heating or hot water. The fan’s job is to push harmful gases away from your boiler and into the flue to ensure the gases safely leave your home. If the fan is faulty, your boiler won’t ignite and will go into lockout.

A boiler lockout is a shut-down procedure that occurs when your boiler detects an issue within the system. Older boilers tend to be more prone to boiler lockouts, which can happen for several reasons, including a fault with the fan.

If you cannot hear the fan working, avoid turning on your boiler because it can be dangerous. The next step you need to take is to call a Gas Safe registered engineer.

5. Faulty gas valve

A boiler won’t be fully functional if it has a faulty gas valve, which controls the flow of gas to the burner and pilot jet. The boiler’s PCB (printed circuit board) controls the gas valve and the other electronic components.

When the gas valve develops a problem, such as a blockage, seizure or damaged wire connection, the supply can be interrupted and cause a range of issues, including ignition failure.

You need to contact a Gas Safe registered engineer to assess the situation, find the problem, and fix it.

6. Pilot light problem

If the pilot light on your boiler isn’t firing up or repeatedly goes out, the cause is probably dirt or debris blocking the jet. The pilot light is the blue flame you can see flickering inside your boiler that ignites the gas. Modern boilers usually display an error code if there is a problem with the pilot light.

A Gas Safe registered engineer might just need to remove the jet and clean it to solve this problem, or they may need to replace it. Pilot light jets are tiny and usually inexpensive to replace.

7. Frozen condensate pipe

The condensate pipe is usually located somewhere outside your property. Its job is to lead the acidic wastewater away from your boiler and down a drain. By being outside, the condensate pipe can freeze in winter, which can cause a blockage and prevent your boiler from igniting.

When the condensate pipe freezes, you may notice strange gurgling sounds coming from your boiler. Your boiler might also show an error code on the display if the pipe is frozen, depending on the make and model you have.

You can thaw a frozen condensate pipe yourself by applying heat to it, such as a heat pack or hot water bottle. Do not use boiling water to unfreeze the frozen pipe as you could damage it. You may need to reset your boiler to get it working again once you finish thawing the condensate pipe.

8. Insufficient gas pressure

Insufficient gas pressure can lead to a boiler ignition problem, so you must get a gas engineer to test the pressure and find out the cause of this issue. Your boiler should lock out and show a fault code if the gas pressure isn’t correct.

If your boiler won’t ignite during cold weather, your gas meter could be the culprit because it can freeze up in low temperatures.

Your boiler might just need a quick reset

If your boiler won’t ignite and is in lockout mode, it may display an error code. You might succeed in clearing the code and solving the problem simply by resetting your boiler. Not all boilers reset in the same way, and you can learn how to reset your boiler by referring to your user manual.

Resetting your boiler may only be a temporary fix. If your boiler keeps locking out after you reset it, you should call in a Gas Safe registered engineer to diagnose and repair the underlying fault.