If your boiler has shut down unintentionally, it may have encountered a problem during operation and gone into lockout. Read on to learn about boiler lockout causes and potential fixes.

Modern boilers feature safety features and can automatically shut down or lockout when they detect an issue with the system or a component.

A boiler lockout can occur when the boiler detects a fault that could damage internal components or present safety risks if it continues operating.

Studies show that boilers deteriorate with age due to wear and tear and degradation and may present with more frequent faults and part failures. Safety features like boiler lockouts can kick in if there’s something wrong with your boiler.

This guide explores various boiler lockout causes and potential fixes so you can know what to do and how to get it sorted as soon as possible.

As with any boiler matter, if you do not feel confident investigating and addressing the issue, it’s highly recommended that you call a Gas Safe registered heating engineer to assist.

Boiler Lockout Causes and Potential Fixes Quick Takeaways:

• Boiler lockouts prevent problems from becoming dangerous for your home or the boiler.
• When it shuts down due to a lockout, the boiler’s display panel can show various fault or error codes and flashing lights.
• The manual contains a list of all possible fault codes and explains their meanings to help you identify the cause and the right course of action.
• Common boiler lockout causes include a faulty pump, ignition failure, a blocked heat exchanger, frozen water, water pressure issues, fan problems, system blockage, a lack of power, and human error.
• While some causes are fairly simple and easy to resolve, many require a qualified heating engineer to diagnose and fix.

What Happens During a Boiler Lockout?

As mentioned, the boiler lockout process is a safety feature that initiates to prevent faults from escalating.

When a boiler is in lockout, it will shut down and stop working. Boilers also provide a visual display that there has been a lockout.

Depending on the boiler’s make and model, it can have flashing lights or display an error code on the panel.

Boiler lockouts prevent problems from becoming dangerous for your home or the boiler and eliminate the risk of fire, boiler explosions, and component damage.

It’s basically a safeguard that deactivates the boiler and prevents it from starting up if there’s an issue.

Wondering which boiler manufacturers performed best? Check out our best boiler brands guide for the full rundown, and if you are trying to determine who the best boiler installation company is, check out our Warmzilla and Boxt reviews.

Boiler Lockout – What should you do?

Following the right process can help you identify the cause of a boiler lockout, whether you experience it once or intermittently.

Once you identify the cause, you can fix it or escalate it to a Gas Safe registered heating engineer. The process is as follows:

Step 1 – Identify the Fault Code or Light Sequence

Apart from the boiler not firing up, it can also show various fault or error codes and flashing lights on the display panel.

If you have a new model with a display panel, it will show an error or fault code, usually a number or string of letters and numbers. Older models can show red or green flashing lights.

Codes can differ depending on the model and brand of your boiler, so ensure you have the boiler manual handy.

The manual will contain a list of all possible fault codes and explain their meanings to help you identify the cause and the right course of action.

If you can’t find the boiler manual or it doesn’t contain the fault code, you can visit the manufacturer’s website or search for the code for the boiler’s make and model online.

You can also contact the manufacturer if you have an older model that doesn’t show fault codes.

The table below shows examples of fault codes from an Ideal Logic boiler:

Fault Code	Description	Solution
L2	Ignition Lockout	Check the gas supply and pilot light; consult a qualified engineer if unresolved.
F2	Flame Loss	Check the gas supply and pilot light; ensure the gas valve is open.
F1	Low Water Pressure	Check and refill the boiler to 1.5 bars; repair any leaks.
L6	False Flame Lockout	Reset the boiler; check the flame detection mechanism.

Step 2 – Find and Fix the Issue

Whether your boiler flashes lights, displays a fault code, or both, the first step in solving the problem is identifying the cause.

There are many reasons why a boiler could lock out, from a simple glitch or power cut to something more serious such as low pressure or safety concerns.

Here are some common boiler lockout causes and potential fixes:

Boiler Lockout Causes and Potential Fixes

Faulty Pump

The pump inside the boiler can blow seals, freeze, or fail due to wear and tear and require replacing.

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

A faulty pump can cause your boiler to shut itself off since water will not be moving around the heating system correctly.

The boiler will shut off to prevent overheating, which in severe cases can out the unit at risk of explosion.

Since the pump is inside the boiler unit, you’ll need to call a Gas Safe registered heating engineer to explore the matter.

Ignition Failure

Three unsuccessful ignition attempts can also lead to boiler ignition lockout.

It can result from a faulty gas valve, low gas pressure or too much gas, damaged wired connections, or faulty ignition leads and flame sensor probes.

Check the probe and ignition leads to determine if the problem is there.

These parts are inside the boiler so you shouldn’t try a DIY fix. You’ll need to call a Gas Safety registered heating engineer to investigate and fix the issue.

They can test the electrode and ignition lead and replace them if necessary, or clean the flame sensor probes and ignition leads if they’re causing the problem.

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

Water Pressure Issues

If the pressure is too low or too high, the boiler can initiate a lockout to protect the internal parts from damage. It will also display a fault code.

Boilers require the water pressure to be just right, typically between 1 and 2 bars.

Low pressure generally results from a system leak. The leakage can occur beneath the boiler, on a radiator, or even in a pipe joint. If a leak is present, the boiler will turn itself off sooner or later.

You can try to fix the leak if its small, provided you have the right knowledge and skills.

Ensure you take the right safety steps like turning off the boiler and isolating the power at the mains.

You should also review the specific instructions for your type of boiler before making any pressure adjustments. You can find them in the boiler’s manual or by searching online for the instructions for the relevant make and model.

Water pressure issues can differ and damage the boiler’s internal parts.

Therefore, if the boiler does not stabilise at the set pressure, you should call a specialist engineer to review the system and advise on the next steps.

No Power to the Boiler

Boilers need a small amount of electricity to ignite.

A boiler ignition lockout can occur due to a loss of power caused by a local outage, blown fuses, or a tripped switch within the property.

You can fix it by ensuring all fuses are working and that the switch where the boiler is connected is on.

In rare cases, the power outage may be traced back to the boiler’s Printed Circuit Board (PCB). You may need to replace it to ensure all electronic components work safely and efficiently.

System Blockage

System blockages from debris or sludge accumulation in the boiler, radiators, or pipework can cause a boiler ignition lockout.

It can also result from frozen pipes in the winter months or on cold mornings. Limescale can also build up and block the boiler’s heat exchanger and other components.

You can easily fix it if it’s a frozen pipe, and you can defrost it manually. Otherwise, you’ll need to hire a professional heating engineer to investigate the cause safely and flush any sludge or debris from the system.

Sometimes, blocked parts can be cleaned, but damage may have occurred, and you may need to replace them.

What size boiler is right for your home? If you are considering a combi boiler, it is largely determined by the number of radiators in your home.

Check out our complete guide to new boiler installation here if you are wondering about the best type of boiler for your home. 

How much may a new boiler cost? Are you considering converting from a conventional to a combi boiler? Use our boiler installation cost calculator to get an estimation.

Heat Exchanger Blockage

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

Blockages in the heat exchanger can restrict water flow and cause your boiler to overheat, resulting in boiler lockouts.

A common sign of heat exchanger blockage is a whistling sound from the boiler.The build up of limescale is sometimes called kettling as it can cause sounds resembling a kettle’s whistle.

In some situations, an engineer can flush out the system and clear any limescale from the system.

However, the limescale build up can cause damage to the part itself and you may need to replace it.

Fan Problems

If the boiler detects that the fan isn’t working correctly, it will lock out.

The fan’s purpose is to create a draught that pushes out the harmful emissions and gases that the boiler produces into the boiler flue. The flue then carries them outside your home and disperses them into the atmosphere.

If the boiler’s CPB determines the fan isn’t operational or is faulty, it can initiate a boiler lockout since it would be dangerous to let the boiler continue running.

You can easily notice whether the fan has malfunctioned because it normally makes a slight noise when in operation.

If you can’t hear any sound, a faulty fan may be causing the boiler ignition lockout. You’ll need to call a specialised heating engineer to confirm the diagnosis and investigate fixing the fan.

Usually, a replacement fan is an expensive part to source. A new boiler may be a more cost-effective option, depending on the age and condition of the boiler.

Frozen Water

Frozen water in pipes, the boiler itself and the condensate pipe can create a blockage which can cause boiler lockouts.

Pipes can freeze if exposed to especially cold temperatures. When this happens, the water will have nowhere to go as a result of the frozen water acting as a blockage.

The water can back up into the boiler, causing it to lockout as a means of preventing damage.

The boiler can then display a collection of fault lights or a fault code, depending on the type of boiler you have.

Another piece of evidence of a blocked condensate pipe is if you hear a gurgling noise coming from the boiler.

You can thaw the pipes with warm water if you suspect they’re frozen, provided you have the right skills and knowledge and understand the necessary safety steps.

Human Error Issues

Human error can occur when you forget some simple settings or obligations that can cause a boiler lockout. These include:

• Thermostat settings – The thermostat controls the temperature the boiler will activate upon (if programmed to be running) and how much it will heat the property. The boiler may fail to start if the thermostat is set too low.
• Timer clock and programme – As briefly mentioned above, a boiler often has a programme that controls when the boiler should operate. If the boiler clock or the programme is incorrect, the boiler will not turn on.
• Prepayment meter – If the boiler has a prepayment meter associated with it, you should check to ensure it has credit to enable the heating system to work.

Step 3 – Reset the Boiler Following a Lockout

After identifying the cause of the lockout and fixing it, you should try to reset the boiler.

The resetting process following a lockout will vary depending on the boiler’s make and model. Therefore, it’s always recommended that you refer to the manufacturer’s manual when you need to perform a reset.

Modern boilers usually have a reset button on the display panel or somewhere near it.

You may need to press and hold the reset button for up to 10 seconds before releasing it to allow the internal parts and processes to activate and restart.

Older boilers may not have built-in reset features, so you may need to consult your boiler manual to learn how to restart the device.

Here’s how you can reset different types of boilers:

How To Reset A Valliant Boiler

The reset button on most Valliant boilers is found on the control panel, below the digital display. To reset:

• Press and hold the reset button for 6 to 8 seconds.
• Check if you can hear the boiler working or if the flame has ignited.
• If an error code was displayed before resetting, check to see if has cleared.

If the boiler fails to restart or the error code still displays, contact a Gas Safe registered engineer.

How To Reset A Baxi Boiler

Baxi boilers usually show a red that constantly flashes or illuminates when your boiler enters lockout. To reset:

• Press the reset button until the red light disappears.
• You can also turn the temperature knob fully anticlockwise.
• Hold the knob until the red light disappears, and turn back to the desired setting.

If your boiler uses a switch:

• Turn the switch to the R (Reset) position.
• Hold for 5 seconds and release.
• The error code should be replaced by the boiler’s temperature reading.

How To Reset A Glow-Worm Boiler

The reset button on a Glow-Worm boiler is usually a red button located on the front or side of the boiler. To reset:

• Press and hold the button for 10 seconds.
• The boiler should start up again.
• Call a registered engineer to diagnose the issue if it doesn’t restart or the fault code persists.

How To Reset A Vokera Boiler

A red light will start flashing when a Vokera boiler encounters a fault or goes into lockout. To reset:

• Find the mode selector switch.
• Turn it to the OFF/RESET position.
• Turn it back to the ‘heating and hot water’, or ‘hot water only’ position.
• Allow at least 2 minutes before turning back to the reset position.

If you constantly need to reset the boiler, it may have a fault. Using fault codes, you’ll need to figure out the cause and fix it or call a registered engineer.

How To Reset A Worcester Bosch Boiler

• Press and hold the reset button on the boiler’s control button.
• Hold the button down for 3 to 5 seconds.

You can also use the feature light to reset it through the following steps:

• Turn the dial down until you reach the reset light
• Hold for 3 to 5 seconds until it returns to its original position.

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, you need to call a qualified engineer would need to attend to investigate further and identify the root cause and address it.

Boiler Lockout Causes & Potential Fixes Summary

As with anything, prevention is better than cure. Modern boilers have an excellent record for reliability and can run for years with regular maintenance. Having your boiler serviced annually is a great way to keep it in tip-top condition and working to it’s maximum efficiency.

Regular servicing ensures any small issues can be rectified before they develop into a boiler lockout. Boiler lockouts can occur due to various reasons. 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, you may want to consider a boiler replacement, especially if it’s old and prone to frequent breakdowns and repairs.

Sources and References

• https://www.sciencedirect.com/science/article/pii/S019689041730016X