Boiler ignition fault: Common issues and how to fix them

Updated on 10th November 2026:

Kieran Haig

Technical Repair Engineer, British Gas

Why won't my boiler ignite?

There are a few reasons your boiler might not be igniting, including:

• Low boiler pressure
• A problem with the gas supply 
• A frozen condensate pipe 
• An ignition or flame detection fault 
• A problem with the thermostat or heating controls 
• A power cut or another problem with the electricity supply
• A blocked flue 
• The boiler’s locked out 
• An internal fault 

You can safely check some of these yourself. Just don't remove the boiler cover or try to repair any parts inside. Anything involving gas must be done by a Gas Safe registered engineer.

How can I tell if my boiler isn’t igniting?

Signs that your boiler might not be igniting include:

• You have no heating or hot water
• You hear repeated clicking or the boiler trying to ignite
• The pilot light has gone out, if you have an older boiler with a permanent pilot light
• The boiler starts but then switches off
• An error code, warning symbol or flashing light appears

Common reasons your boiler won't ignite

Low boiler pressure

Your boiler needs the right water pressure to work properly. If it drops too low, it might not ignite. When the boiler's cold, the gauge should usually read between 1 and 1.5 bar. Your manual will tell you the right level for your boiler.

If it's below 1 bar, you can usually top it up yourself by following the manufacturer's instructions. If it keeps dropping, contact a Gas Safe registered engineer.

Problems with the gas supply

If your boiler isn't getting gas, it won't be able to ignite. See if your other gas appliances, like your hob, are working. And if you have a prepayment meter, make sure there's enough credit on it. It's also worth looking at your gas meter for any messages or errors.

If your gas supply seems fine but your boiler still won't ignite, contact a Gas Safe registered engineer.

A frozen condensate pipe

Your boiler’s condensate pipe carries waste water away. If part of the pipe is outside, it can freeze during very cold weather and stop your boiler working. You might also hear a gurgling noise.

If you can safely reach the pipe from ground level, check your boiler’s manual for instructions on thawing it. You may be able to use a hot-water bottle or warm (not boiling) water. Only reset your boiler afterwards if the instructions recommend it.

Your boiler’s locked out

Your boiler may lock itself if it detects a problem.It is a boiler safety feature designed to protect the appliance and its users. You might see an error code, warning light or message on the display.

Check the manual for your make and model and only reset the boiler if the instructions recommend it. If it keeps locking out, contact a Gas Safe registered engineer.

A problem with the ignition or flame detection

If your boiler can’t ignite or keep a stable flame, there could be a problem with one of its internal parts. This will need to be checked by a Gas Safe registered engineer.

An issue with your thermostat or controls

Your thermostat tells the boiler when your home needs heating. Before calling an engineer, there are a few things you can check.

• The thermostat is switched on
• It’s set higher than the current room temperature
• Your heating schedule is set correctly
• If you have a wireless thermostat, check that the batteries don't need replacing'

A problem with your power supply 

Your boiler needs electricity to work, even though it runs on gas. Here are a few things you can check.

• The boiler’s switched on the display is lit up  
• Nothing’s tripped in your fuse box
• The rest of your home still has power

Don't open up any electrical parts or try to fix them yourself. If your power supply is working but your boiler still won't ignite, contact a Gas Safe registered engineer.

A problem with the flue

If the flue looks blocked or damaged, switch the boiler off and contact a Gas Safe registered engineer. Don’t try to inspect, unblock or repair it yourself.

Things to check if your boiler won’t ignite

Here are some basic checks and boiler fixes you could try if your boiler won’t ignite: 

1. Look at the display

If there's an error code, warning symbol or message saying the boiler's locked out, take a photo or make a note of it. Your boiler manual will tell you what it means.

2. Check the boiler pressure

When your boiler's cold, the gauge should usually read between 1 and 1.5 bar. Your manual will tell you the right level for your boiler.

3. Check your thermostat

Make sure it’s switched on, set higher than the current room temperature and that your heating schedule is set correctly.

4. Make sure your gas supply is working

See if your other gas appliances, like your hob, are working. If you have a prepayment meter, check there's enough credit. And look at your gas meter for any messages or errors.

5. Check if your condensate pipe is frozen

If it is, you may be able to thaw it with a hot-water bottle or warm (not boiling) water. Only try this if you can safely reach the pipe from the ground.

6. Reset the boiler

Follow the steps if your boiler manual recommends it. But if the problem keeps coming back, don't keep resetting it as it won’t fix the underlying problem.

7. Get help if your boiler still won’t ignite

Contact a Gas Safe registered engineer. Don't take the cover off your boiler or try to fix anything inside it yourself.

Why does my boiler ignite and then turn off?

It’s normal for your boiler to stop firing once your home reaches the set temperature. But if it repeatedly starts and stops over a short period, or tries to ignite and then shuts down, there could be a problem. If this keeps happening, contact a Gas Safe registered engineer.

Potential causes of short cycling / failed ignition include:

• Low system pressure
• Circulation issues
• Flame detection problems
• Internal component faults 
• Overheating.

If your boiler repeatedly short cycles or fails to ignite, call a qualified engineer. 

Why do I have hot water but no heating?

If you have hot water but no central heating, there could be a problem with your thermostat, heating schedule or controls. Check that they’re set correctly. If your heating still doesn’t come on, contact a Gas Safe registered engineer.

Why won't my boiler ignite but the pilot light is on?

The pilot light on a boiler is a small, continuously burning flame that ignites your system's main burner whenever central heating or hot water is requested. 

Older boilers may have a permanent pilot light, while most modern boilers use electronic ignition. If the pilot light on an older boiler is on but the main burner won’t ignite, there could be an internal fault. Contact a Gas Safe registered engineer to take a look at it.

When should I call an engineer?

Contact a Gas Safe registered engineer if:

• Your boiler keeps failing to ignite
• The same error keeps returning
• Your boiler keeps locking out
• The pressure keeps dropping
• The boiler’s leaking
• The boiler keeps overheating
• The flue looks damaged or blocked
• You’re unsure about any of the checks

Smell gas or suspect carbon monoxide?

If you smell gas, open doors and windows, avoid flames and electrical switches, and call the National Gas Emergency Service immediately on 0800 111 999. If a carbon monoxide alarm sounds, get everyone into fresh air and seek medical help if anyone feels unwell.

How to help prevent boiler ignition problems

You can help keep your boiler working properly by:

• Getting it serviced every year by a Gas Safe registered engineer
• Asking an engineer whether an external condensate pipe needs extra insulation
• Checking the pressure from time to time and repressurising it if needed 
• Bleeding radiators when they have cold spots
• Getting recurring warning symbols, leaks or unusual noises checked by a Gas Safe registered engineer

Need help?

If your boiler still won’t ignite or isn’t working properly, our expert engineers are here to help.