Boiler Lockout Causes & Potential Fixes

Last updated: November 15, 2023

A boiler can lockout due to many causes, however, the lockout process is a safety mechanism to protect the boiler’s components and ultimately the household from danger.

During this article, we will discuss the causes of boiler lockout as well as explore some troubleshooting tips to locate the source of the matter and fix it, if it’s safe to do so.

As with any boiler matters, if you do not feel confident to investigate and address the issue, we highly recommend that a Gas Safe registered heating engineer is called out to assist.

What Happens During a Boiler Lockout?

As mentioned, the lockout process on a boiler is for safety purposes, to help protect from a potentially dangerous incident, escalating to either a fire or a dangerous gas leak.

When a boiler locks out, it will shut down and stop working. Often the boilers will also provide a visual display that there has been a lockout either by flashing lights or by displaying an error code on the panel on the unit, depending on the make and model of the boiler.

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Boiler Lockout – What should you do?

Should you experience a boiler lockdown either as a one-off, or intermittently, there is a process to follow to identify the cause and from there, either fix the matter yourself or escalate the issue to a Gas Safe registered heating engineer. The process is as follows:

Step 1 – Identify the Fault Code or Light Sequence

As mentioned, the boiler will visually display the fact that a lockout has occurred and the first step will be to identify the reason behind this by finding the error code or flashing light sequence within the boiler’s manual. Should you no longer have the boiler’s manual, search the make and model of the boiler and error code online to find out more.

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Step 2 – Find and Fix the Issue

Hopefully, the manual or internet will have determined which fault the boiler is suffering from and therefore you can proceed with finding out how to fix the matter.

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You may also find our review of the best eco-friendly boilers of interest.

Boiler Lockout Causes

Faulty Pump

The pump inside the boiler can blow or seize, or simply suffer from wear and tear and require replacing.

Another common fault with central heating pumps is that they can become blocked with debris.

As the pump is inside the boiler unit itself, a Gas Safe registered heating engineer will be required to explore the matter.

Ignition Failure

Most models of boilers will attempt to ignite three times before locking out. There can be many causes of an ignition failure; from a blocked gas valve or burner to a faulty fan or ignition lead.

Again, all of these failures are on parts or processes inside the boiler and therefore should not be explored yourself, and a qualified heating engineer should be called.

Got a common boiler problem? Check out our quick fix guide on boiler lockout, boiler ignition faults, boiler PCB faults, faulty diverter valves and boiler timer issues.

Water Pressure Issues

Boilers require the water pressure to be just right, typically between 1 and 2 bars of pressure otherwise the boiler will lockout.

Should the pressure be too low, you can attempt to re-pressurise the system by the use of the taps, which are usually located underneath the boiler.

It is recommended that the specific instructions for your type of boiler are reviewed before making any pressure adjustments, either by reviewing the boiler’s manual or searching online for the instructions for the relevant make and model.

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Ongoing water pressure issues can cause damage to the boiler’s internal parts and therefore if the boiler does not stabilise at the set pressure, it would be highly recommended that assistance is sought from a specialist engineer to review the system and advise the next steps.

No Power to the Boiler

There are a number of reasons why there is no power supply to the boiler. There are some simple causes such as; a power cut, the pre-payment meter has no funds or tripped fuse, or more complex matters that would require a Gas Safe Registered heating engineer to be called out, such as a fault with the PCB – the motherboard of the boiler.

System Blockage

There are a number of ways that debris can cause blockages either inside the boiler itself, within the flue or in the pipework of the heating system.

On colder mornings, one initial check could be to ensure that the external condensate pipe has not frozen. If it has, try wrapping around some rags or pouring over warm water to defrost the pipes.

If there is no sign of an external blockage there could be an issue inside the boiler itself or the pipework and therefore a heating engineer would need to be called out.

In some cases, the engineer may suggest that a chemical flush is performed to clear the system of any limescale or debris build-up.

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Heat Exchanger Blockage

The heat exchanger is a component within a boiler unit that can become blocked due to debris or limescale that has built up in the system.

Blockages can result in the water temperature being too warm, which in turn causes the boiler to lockout.

In some situations, an engineer can clear the heat exchanger of any blockages, however more commonly the limescale build up can cause damage to the part itself resulting in a replacement being required.

Fan Problems

If the boiler detects that the fan inside the boiler is not working correctly, it will lock out. The fan’s purpose is to move the waste gases from the boiler into the flue, and outside the property and if it is not working properly, the safety mechanism ensures that the boiler shuts down to prevent the dangerous gases leaking into the property.

Reset the Boiler Following a Lockout

The resetting process following a lock out will vary depending on the make and model of the boiler itself, therefore it is always recommended that you refer to the manufacturer’s manual when a reset is needed.

Once the boiler reset has been undertaken, a couple of minutes will be required to enable the boiler to reignite and re-pressurise, before it is known whether or not the troubleshooting has worked.

Step 4 – Troubleshooting if the Boiler won’t Reset

Should the boiler not restart after the resetting process has been completed, there could be a faulty component causing the subsequent lockout. At this stage, a qualified engineer would need to attend to investigate further.

Boiler Lockout Causes & Solutions Summary

During this article, we have explored a range of reasons that can cause a boiler to lockout. While some are fairly simple and easy to resolve, many require a qualified heating engineer to safely open the boiler unit itself and explore what is causing the issue.

If your boiler is a repeat offender, it may be worth looking into a boiler replacement.