Modern boilers are designed to lockout when they detect a fault within the boiler of the central heating system. Read on to learn more about boiler lockout causes.
Boiler lockouts can be incredibly inconvenient, preventing you from using the heating, hot water, or both until the matter can be resolved.
Boiler lockouts can occur more frequently if you have an old or faulty boiler, so it’s worth considering a modern, more efficient boiler to save up to £475 on fuel costs.
During a boiler lockout, your boiler effectively shuts down, indicating a problem with the boiler of heating system. The feature acts as a safeguard that protects the boiler and prevents the issue from becoming dangerous.
A number of reasons could cause a boiler to lock out and, subsequently, not fire up.
This guide explores various boiler lockout causes and how to identify them so you can act fast and get your heating and hot water back up and running.
Boiler Lockout Causes Quick Takeaways:
- A boiler lockout is a safety mechanism that shuts off the boiler when faults are detected.
- Depending on the boiler’s make and model, it can have flashing lights or display an error or fault code during boiler lockouts.
- The manual can help you identify the meaning of the fault or error code or flashing light so you can know how to solve it.
- 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 you can resolve some easy causes, most require a qualified heating engineer to diagnose and fix them.
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What is a Boiler Lockout?
A boiler lockout is a safety mechanism that shuts off the boiler when faults are detected. This process ensures that the fault does not cause further damage to the boiler components.
Boiler lockouts initiate automatically when the boiler detects faults that can cause damage to internal components or present safety risks to your home if it continues operating.
There are many internal parts within a boiler, each with different tolerance levels for what is classified as a fault that could cause a boiler lockout.
If you’re currently experiencing a boiler lockout, don’t panic. Identifying which part is causing the shutdown can help you determine the most appropriate next steps to resolve the matter.
Did you know your boiler’s efficiency can impact the amount of energy it uses and, ultimately, your heating bill costs? Check out our guide to the best condensing boilers to learn more.
You may also find our review of the best eco-friendly boilers of interest.
What Happens During a Boiler Lockout?
The boiler lockout process is a safety feature that initiates to prevent faults from escalating.
The PCB (also known as the boiler’s motherboard) usually detects a cause for concern and initiates a shutdown.
Meanwhile, the PCB will attempt to identify the cause of the fault and provide a visual display or message.
Depending on the boiler’s make and model, it can have flashing lights or display an error code on the panel. This helps eliminate guesswork when identifying the problem with the boiler.
To determine the type of fault, check the error message or series of lights in the boiler’s manual. If you no longer have the manual, search the Internet for the specific code and model.
What Should You Do In A Boiler Lockout?
If your boiler locks out either just once or has been doing so intermittently, follow the steps below:
#1 Identify the Meaning of 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. |
#2 Follow the Instructions in Order to Fix the Fault
Whether your boiler flashes lights, displays a fault code, or both, the first step in solving the problem is identifying the cause of the lockout.
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.
If your code relates to one of the common causes mentioned below, please follow the troubleshooting advice:
Common Boiler Lockout Causes
#1 Faulty Boiler Pump
A pump can develop a fault for a number of reasons, including debris causing a blockage, a leak starting, or a blown seal.
A faulty pump can cause your boiler to shut itself off because water is not moving around the heating system correctly.
The boiler will shut off to prevent overheating, which, in severe cases, can put 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 assess the pump and advise on the next steps.
#2 Failure to Ignite
A failure to ignite can be caused by a number of issues. These include a faulty gas valve, low gas pressure or too much gas, damaged wired connections, or faulty ignition leads and flame sensor probes.
Most boiler brands are set up to try to ignite three times before locking out.
The parts that can cause an ignition failure 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 ignition faults, PCB faults, faulty diverter valves, and boiler timer issues.
#3 Boiler 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.
If the leak is small, you can try to fix it, 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.
#4 No Power to 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.
#5 Blockages Within the Boiler System
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.
If it’s a frozen pipe, you can easily fix it by defrosting 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.
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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.
#6 Fault with Heat Exchanger
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 buildup 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, limescale buildup can damage the part itself, and you may need to replace it.
#7 Boiler 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 that the fan isn’t operational or is faulty, it can initiate a boiler lockout, as 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 expensive to source. Depending on the age and condition of the boiler, a new boiler may be a more cost-effective option.
#8 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 because the frozen water will act 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.
If you suspect the pipes are frozen, you can thaw them with warm water, provided you have the right skills and knowledge and understand the necessary safety steps.
#9 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.
Resetting the Boiler
Once you identify the relevant boiler lockout causes and rectify it, you’ll need 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.
Boiler Lockout Causes Summary
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.
While some boiler lockout causes can be resolved easily, others may result in a costly replacement part. It is always better to err on the side of caution and call a professional should the lockout keep reoccurring or if you suspect a part failure.
Through regular maintenance, you can also prevent various boiler lockout causes and keep your boiler running excellently for years. Having your boiler serviced annually is a great way to keep it in tip-top condition and working to its maximum efficiency.
A regular service can ensure any small issues are identified and rectified before they develop into a boiler lockout.
Further reading:
- Smell of gas from boiler.
- Boiler leaking water.
- Boiler lockout.
- Boiler PCB faults.
- How to fix a faulty diverter valve.
- Compare BOXT boiler prices.
Sources and References
- https://energysavingtrust.org.uk/advice/boilers/