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Boiler not igniting? Common issues and how to fix them

woman doing washing with a boiler in the background

If your boiler won’t turn on, you could be left without heating and hot water until the issue is resolved. We understand that this can be a real nuisance for the whole household, so we’ve put together this guide to help you find the problem and work out how to fix it.

There are several possible issues that could prevent your boiler from igniting. We’ll look at each of these in turn over the course of this guide. As well as helping you to identify the problem, this post also explains some common tricks you can try before calling an engineer.

Never attempt to mend any part of your boiler on your own. If you suspect that your boiler has a fault, you should always call a Gas Safe-registered engineer to take a look. Find an installer to fix your boiler. Alternatively, visit our boiler repair page for more information.

Why is my boiler not turning on?

There are a range of reasons why your boiler might not be turning on. Here, we’ve explained the possible options starting with those which occur most often.

Your home may already be at the temperature you’ve set

The most common cause of a boiler not igniting is that your home has already reached the temperature you’ve set on the thermostat. If the temperature is set to 18°C and your thermostat shows that the house is at 19°C, the boiler won’t come on as your home has already been heated to the requested temperature.

Don’t worry if this is the case – just set the desired temperature to 20°C (i.e. above the current temperature in your home) and you should find that your boiler turns on. If this doesn’t work, then read on to learn more about the other problems that could be preventing your boiler from igniting.

Electrical problems

Your boiler needs electricity to ignite. In many cases, our engineers find that a boiler not coming on is a sign of an electrical problem (and nothing to do with the appliance itself).

Your power could be out

Do the other parts of your home still have electricity? If the lights and electrical appliances elsewhere in your home aren’t working, it might be that you have a power cut (particularly if you’ve had heavy snow, strong winds, or other extreme weather conditions). In this case, your boiler won’t work until your electricity is up and running again.

Sometimes an overnight power outage can cause your boiler's programming to reset. This might change the time settings that control the appliance, preventing it from coming on as it should in the morning. If your boiler won’t ignite, it’s worth checking that the control panel settings are correct and as you’d expect them to be before considering any other possible issues.

Tripped fuse

A tripped fuse in your consumer unit could also be preventing your boiler from getting the power it needs. Find the consumer unit in your home and make sure that all of the fuses are switched on. Additionally, make sure the isolation switch next to your boiler is turned on.

Issues with your gas supply

Your boiler needs a certain gas pressure to run, therefore issues with your gas supply such as insufficient or no gas pressure can result in your boiler not igniting and displaying a fault code.

Issues with your boiler

There are several issues that could affect your boiler and cause it to stop igniting, such as faulty fan or gas valve, frozen pipes and others discussed in the following section. Try checking if your gas oven or hobs are turning on to check if your home has a sufficient supply.

No pilot light

If your boiler isn't igniting, it's likely that there is no pilot light. A common cause of pilot light going out is a blocked jet. Pilot light’s jet is small and can easily get blocked with even the slightest bit of debris. The good news is that the jet can be cleaned or easily replaced by a Gas Safe Engineer.

Your burner could be blocked

A burner can get blocked due to the production of carbon monoxide which occurs when a boiler burns gas. If your boiler’s burner is blocked, you have a couple of options to fix this issue depending on the burner's current condition. For a burner in a good condition, it may be possible to simply clean out the blockage, however, if the burner is in a bad condition, it is advisable to replace it completely.

Faulty fan

A boiler fan extracts combustion gases from your boiler. If your fan is faulty, the boiler won’t ignite as a safety precaution. If you suspect that your boiler fan is faulty, it is important to not turn on the boiler and get it repaired as soon as possible.

Faulty gas valve

A gas valve is a device that allows gas to flow into a burner or appliance. If the gas valve is faulty or blocked, it may not allow gas to flow properly, which could stop your boiler from igniting. A gas valve that does not close properly can allow gas to escape, posing a fire hazard, contact an engineer to repair this issue as soon as possible.

Frozen pipes

If even the slightest bit of water is frozen in the pipes, it will block the pipes and the boiler will not ignite and be able to produce heat. To fix this, the pipes will need to be thawed. Once the pipes are thawed, the boiler should start working again.

Common fixes before calling an engineer

There are a few simple and safe boiler fixes you can do yourself before calling an engineer.

  • Check the pilot light

    The pilot light is a small flame that should be lit in your boiler. If it's gone out, you can relight it following the manufacturer's instructions. However, bear in mind a modern condensing boiler will not have a pilot light. So if your boiler is new it is unlikely to be this.
  • Check the thermostat

    The thermostat is the device that tells your boiler when to turn on and off. If it's not working properly, your boiler may not be heating your home enough. You can test the thermostat by turning it up and down and seeing if the boiler responds.
  • Try resetting the boiler

    If your boiler is not working, you should always try resetting it as it might be the simplest fix. If the boiler doesn’t re light after 2 or 3 attempts, it is advisable to call a qualified engineer to find out what the problem is and avoid any further issues.
  • Check the pressure

    If the pressure in your boiler is too high or too low, it can cause problems. You can check the pressure using a pressure gauge. If the pressure is too high or too low, you can adjust it using the boiler's manual.

Why you should never attempt to fix a boiler issue yourself

Attempting to fix a boiler issue yourself can be incredibly dangerous. Boilers contain high levels of heat and pressure, and can cause serious injuries if not handled correctly.

Additionally, if the boiler is not properly fixed, the issue could get worse, leading to even more serious problems. It is always best to call a gas safe engineer to fix a boiler issue, as they will have the experience and knowledge necessary to get the job done safely and correctly.

To mange and book your boiler repair appointments online, register your Vaillant appliance, and activate your smart home subscription, visit myVAILLANT Web online service appointment.

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