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Oil Boiler Not Firing Up? Here’s How to Fix Oil Boiler Lockout

Nick Geary
By: Nick Geary
Updated: 29th September 2023


If your oil boiler is not firing up, or firing but then cutting out soon after, you may have what is called an oil boiler lockout. Here we explain what this means, what could be causing the problem and what you can do to get it sorted ASAP.

What is oil boiler lockout?

When an oil boiler detects that there is a fault in the system (usually via the flame sensor) it will automatically lockout or shut down. It does this when it senses that the fault would cause damage to internal components and/or present a safety risk if the boiler were to continue operating. To check if your boiler is definitely in lockout mode you may see an error or fault code on the display panel or a coloured flashing light.

If you’re still unsure, a heating engineer will be able to help you identify if you have an oil boiler lockout and help you get your boiler back up and running.

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How to fix an oil boiler lockout

Check if a fault code is showing

Each boiler has its own series of fault codes which can often identify the cause of the boiler lockout so you can decide whether or not an engineer is needed.

Check that you have not run out of oil

You may have simply run out of fuel. Check the level of oil in your storage tank either with an electronic gauge or by simply dipping a stick into the tank as you would a dipstick in a car engine. Even if there is a little bit of oil in the tank, it may not be enough to fire the system.

Check the boiler pressure

If the boiler pressure is too low or too high then the boiler may lockout and you will need to adjust the pressure before you reset the boiler. Boiler pressure should be around 1.3 bar depending on the model, but generally all boilers should be between 1-3 bar. If it's too high you may need to bleed water from the radiator bleed valve or the drain cock. If it's too low, you will need to use the boiler pressure gauge to increase it. If you find that your boiler pressure is regularly dropping, you may have a leak which you will need an OFTEC engineer to fix.

Check the condensate pipes/vents

The condensate vents which enable the harmful fumes to escape your home have frozen shut in cold weather. Find out how to thaw a frozen condensate pipe.

Try resetting the boiler

When the boiler locks out it will automatically cut off the oil supply as part of the safety mechanism. If you have oil and you are still suffering with a boiler lockout, try resetting the boiler. It's best to consult your boiler manual for how to do this but it is usually as simple as pressing a button.

If these steps don't solve the issue and your boiler keeps cutting out, you may need to contact a professional heating engineer to diagnose and fix the problem. They may simply need to carry out a service which will include cleaning dirty filters, removing air locks and cleaning blocked nozzles. In some cases, there may be a more severe problem with will require replacement parts or even a boiler replacement.

While you should be able to carry out basic maintenance on your oil boiler such as restarting it or adjusting the pressure, you should never attempt to fix or replace a boiler. Instead you should contact an OFTEC registered heating engineer.

Boiler Guide has a network of qualified heating engineers who can help you with any repairs your boiler needs. We partner with them to make sure you get the best deals in your area. To get access to up to 3 free quotes (with no obligation!) from these engineers, just answer a short form about what kind of work you need done. We’ll take it from there.

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What causes an oil boiler lockout?

Aside from resetting the boiler, checking the boiler pressure and ensuring you have oil in the tank, when you have an issue with a boiler lockout it's likely to be due to general wear and tear or a faulty component caused by poor maintenance. You need to find an OFTEC registered heating engineer to diagnose and fix the problem, but here are some possible causes you might be looking at.

  • A leak in the system is causing low boiler pressure.
  • A fault in the thermostat, e.g. a problem with the radio frequency (RF) pairing means that the boiler does not know when to fire up.
    The fan which works with the flue to expel harmful fumes from your home may be broken, which will cause the boiler to lockout for safety reasons.
  • The air pressure switch, which detects whether the fan is operational, may be broken and again causing the boiler to lockout for safety reasons.
  • The printed circuit board (PCB) which is the brain of the boiler and controls all of the different components may be faulty. This can be hard to diagnose as the boiler's PCB may display a fault code for a specific component when in reality it is the PCB itself which is malfunctioning. This is also the most costly part of the boiler to replace.

How to prevent an oil boiler lockout

Lag (insulate) your condensate pipes

To prevent the condensate pipes from freezing in cold weather consider adding some pipe insulation or lagging to them.

Monitor your oil supply

Running out of oil is a sure-fire way to cause a boiler lockout so make sure you are on top of your level and that your reorder early enough that you won't run out.

Get an annual boiler service

Oil boilers should also be serviced annually by an OFTEC registered heating engineer to keep your home safe, prevent breakdowns and ensure that the boiler is running efficiently. The engineer will carry out safety checks as well as cleaning or replacing any components which may be causing the boiler to run less efficiently. Regular servicing ensures any small issues can be rectified before they develop into a boiler lockout.

Contact us today and we'll put you in touch with an OFTEC registered heating engineer in your area who will provide you with a free no-obligation quote for an oil boiler service.

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Nick Geary

About the author

Nick Geary

Nick has a wide range of experience writing about conventional and renewable heating solutions, and is always increasing his knowledge by researching any new heating technologies on the horizon.

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