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Boiler Not Firing Up? Top Potential Causes


When your boiler decides it’s not igniting, it can be the worst of starts to your morning. No one wants to be left with their central heating not working and no hot water

This is a problem you want to solve quickly, and it’s essential to know the cause to resolve the issue. So, if your boiler is not firing up - before you call a boiler engineer, this guide to the most common causes may save the day. 

An unqualified person should never try to fix a boiler. This guide aims to establish whether your boiler is an easy fix before you call a professional. 

No power

Your boiler uses a small amount of electricity to fire up. If your boiler is not igniting, check the fuse box as there may be a tripped switch, even if the other electric and gas appliances in your home are working. The leading causes of a boiler having no power are:

  • Weather conditions causing a shortage of power
  • Someone accidentally turning the boiler off 
  • The circuit being overloaded

Trapped air

Are the tops of your radiators not heating up very well? That’s a sign of trapped air. Your central heating works by circulating hot air through the pipes and radiators. 

Over time pockets of air develop and rise to the top of the radiator, which can lead to your boiler not firing up as there is trapped air in the system. By bleeding your radiators, you will remove these pockets of air.

Thermostat setting 

Is your boiler not firing up for central heating? If your thermostat is set too low, the central heating won’t come on as the room temperature is higher than the set temperature. Try increasing the temperature on the thermostat and see if your boiler ignites. 


The boiler will only fire up at the precise time it is set to. If you have recently had a power cut, the boiler will reset itself, meaning that it will no longer fire up when you would expect it to. To solve this, reset the timer on your boiler. 

A faulty fan 

Your boiler will not ignite with a faulty fan. The fan in your boiler is used to push harmful gases into a part called the flue for them to exit your home safely. If the fan isn’t working, it is important that you do not turn the boiler on as this can be dangerous. It’s time to call a professional. 

No gas supply 

Check that the other gas appliances in your home are working. If they aren’t this is because there is an issue with the gas supply to your home. The next step you should take is contacting your gas supplier. 


If your boiler does not have enough pressure, it will be unable to fire up. Check the water pressure gauge on your boiler; this should be set around 1-2.  All boilers lose pressure over time, but a sudden drop indicates that the system has a leak or that the radiators need bleeding. 

If there is a leak in the system, you should immediately turn off the water supply and contact a boiler engineer. If this isn’t the case, you should bleed your radiators. 

A frozen pipe 

The condensate pipes lead acidic wastewater down a drain outside of your property. As the pipes are located outside, they are susceptible to freezing in those cold winter months, which can cause a blockage. 

If there is a blockage, your boiler should display an error code that helps you identify that this is the problem. This issue is often accompanied by gurgling sounds, which can also help you identify it. 

Try to apply heat (e.g. a hot water bottle or heat pack) to thaw the ice to solve the issue. Do not use boiling water as this can damage the pipe. Reset the boiler after thawing the pipe. 

A blockage in the burner 

When a boiler burns, it produces CO2, which can occasionally block up the burner. A blockage in the burner will prevent the boiler from igniting. This issue calls for a qualified engineer. 

A faulty diverter valve

A diverter valve directs the flow of hot water to the heating or taps in your home. If your boiler is working but there is no hot water, a faulty diverter valve is likely to be the issue. 

A diverter valve can stick simply due to wear and tear. You’ll need to call a gas engineer to replace this. 

No pilot light 

The pilot light is the tiny blue flame you see inside your boiler, which ignites the gas. This flame should not be yellow or orange as this is a sign that there is a carbon monoxide leak which is extremely dangerous. 

Without the pilot light, the boiler cannot provide central heating or hot water. It may simply need a clean, however, leave this to a qualified engineer. 

Simply reset your boiler 

Many problems can be solved by simply resetting your boiler. If you are unsure how to do this, refer to your boiler manual.  

BOXT can help 

Is your boiler causing you mayhem? Call us on 0800 193 7777 to speak with one of our senior engineers who’ll help you solve any boiler problem. Alternatively, you can message us on our Live Chat for advice from our heating specialists. 

If you’re a BOXT customer, you can sign up for one of our home cover plans to book a callout and protect yourself from any last minute costs when your boiler’s acting up. 

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