Why Is My Boiler Not Igniting?

In this guide we’ll explain the likely reasons leading to your boiler not igniting, and steps you need to take to get it fixed. 

It’s worth noting, the only people qualified to repair boilers are Gas Safe registered engineers. Attempting to fix any part of your boiler on a DIY basis could be incredibly dangerous; always ring a qualified professional.

‍Why is My Boiler Not Igniting?

Your boiler’s printed circuit board (PCB) monitors the components operating in your boiler. When it notices changes that cause your boiler to run inefficiently or dangerously, it will lock out the appliance and display a fault code. 

Your boiler then won’t ignite until the fault has been fixed and the fault code has been cleared. 

The top reasons your boiler isn’t igniting include: 

• Faulty gas valve
• Restrictions in the gas supply
• Burner has become clogged
• Condensate pipe blockage
• Low water pressure in your central heating system
• A pilot light that keeps going out
• Broken fan

Depending on the fault that’s causing your boiler not to ignite, expect costs to range from £100-£500. 

If you’d prefer to invest that cash into a new, reliable and efficient boiler, you can get a fixed price on-screen by using our clickable tool for new boilers.

Top 7 Reasons Your Boiler Isn’t Firing Up

As you’ll see below, boiler repairs can get very expensive very quickly. If you have an old and unreliable boiler, it might make sense to simply replace it, rather than sinking £500+ into repairing an old one. Our clickable form here takes less than 2-minutes to complete, and will give you a fixed price on-screen for a new gas boiler. 

There are dozens of reasons that lead to a boiler not igniting. Below, we’ll focus on 7 of the most common boiler problems that could be to blame, as well as an estimated cost to have that component repaired.

1. Gas Valve Fault

The gas valve in a boiler controls the supply of fuel. When you turn on hot taps or your central heating, the gas valve opens to allow the correct amount of gas into the system. 

Like any moving component, over time a gas valve can become blocked or stuck. This might stop it from opening or closing completely. As soon as the PCB recognises this fault with the gas valve, it will lock out and your boiler won’t ignite.

If a Gas Safe engineer isn’t able to free up the valve to stop it sticking, a replacement will need to be fitted. Replacement gas valves cost in the region of £250-£300 including labour for the average boiler.

2. No Gas Supply

If your boiler won’t ignite, checking the gas supply is one of the first steps. 

Your boiler engineer will need to test the gas pressure at certain points:

• The point whereby gas feeds into your meter - A problem here could signify a gas supply issue and you’ll need to contact your utility supplier to have it rectified
• Gas supply out of your meter - Like a gas valve, there are components here that can get stuck, meaning your boiler’s gas supply isn’t adequate
• Gas supply into your boiler - If gas is adequate into and out of the meter, your Gas Safe engineer will need to check the supply into the boiler. If it’s inadequate, the gas valve fault mentioned above might be the reason why your boiler won’t ignite

Your boiler’s PCB is able to monitor the operation of every component in your boiler. When it locks out due to a fault, it will display a fault code. 

Essentially, if the fault finding mentioned above has been completed but no fault has been found, the fault code displayed on your boiler should highlight what the issue is. This should give your boiler engineer enough information to understand why your boiler isn’t igniting.

3. Clogged Burner

If your gas boiler isn’t burning efficiently, this could be the reason your boiler isn’t igniting and the cause of a lock out. A buildup of carbon over time could have blocked the burner to a stage where it’s operating both inefficiently and dangerously. As soon as the PCB notices this, it will lock out the boiler and display an error code.

Whilst a Gas Safe boiler engineer will be able to repair most burners, it’s quicker to simply replace it. A new burner costs around £200, with labour being a similar price for a replacement (more for a repair as it takes longer). A new burner in this instance would rectify the problem of your boiler not igniting or firing up.

Obviously this is a substantial investment. If your boiler is over 10-years old, it might be worth considering investing that cash in a new boiler that’s much more efficient. You can get fixed prices on-screen using our clickable boiler installation form here.

4. Condensate Pipe Blockage

Harmful waste gases / fluids are vented from your gas boiler via the condensate pipe. 

If your boiler won’t fire up, it’s worth checking the condensate pipe to check it’s not blocked. This could be a simple blockage caused by leaves or other debris. Even a partial blockage in the condensate pipe is going to cause your boiler to lock out, and your boiler won’t fire up. 

A condensate pipe blockage is much more typical in winter. Gases / fluids venting via the condensate are prone to freezing and this causes a partial blockage. 

If your boiler won’t fire up or ignite and you suspect your condensate pipe is frozen, it can be thawed out using luke-warm water. You should never use hot water, as you risk cracking the condensate pipe.

5. Lack of Water Pressure

If you see a fault code on your display screen that relates to water pressure, it’s likely that your system has a small leak. Usually a boiler can be topped up via the filling loop to increase the boiler’s water pressure. 

However, it’s worth investigating why the boiler pressure dropped in the first place. If your boiler won’t ignite due to low water pressure, almost certainly, there is a leak in the system. 

A quick visual inspection below the boiler, under radiator valves and all sections of pipework in your property should allow you to identify any obvious leaks. Not only will leaks that lead to a drop in water pressure mean your boiler won’t fire up, you could also end up with water damage in your property. 

The fix here could be something as simple as tightening up a radiator valve, or re-soldering a copper joint.

6. Pilot Light Won't Ignite / Stay Lit

Older boilers have a pilot light; this should ignite and stay lit with a blue flame. If it doesn’t, there’s a problem with your boiler. And if your pilot won’t light at all, your boiler’s main gas supply won’t either; you’ll have no heating or hot water.

Common causes of a pilot light going out are a broken thermocouple, but on many occasions there’s a simple explanation; a big draught. If it’s incredibly windy and a gust of wind is able to travel back into the flue, it’s likely to blow out the pilot light. This will mean your boiler won’t ignite. 

As this is a potential gas supply issue, you should contact a Gas Safe registered boiler repair engineer to help fix the problem. ‍

7. Faulty Fan

A faulty fan is one of the most common causes of a boiler not igniting or firing up. The fan plays a multi-purpose role of supplying oxygen to the burner, as well as venting harmful waste gases towards the flue, allowing them to escape from your property. 

‍As a boiler’s fan creates a lot of vibration, there’s a good chance this has led to loose wires and / or connections. If this is the case, it’s a quick and cheap fix to get your boiler fired up again. 

However, if you need a new fan, the costs are substantial. Replacement fan costs tend to be in the £300-£400 range depending on the type of boiler. ‍

If your boiler is old, inefficient and not igniting due to a faulty fan, it’s worth comparing repair costs with replacement boiler costs. Our boiler quotation tool here will give you a fixed price on-screen, with finance available.