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Boiler Lockout: Causes and How to Fix?

Has your boiler decided to lockout? Our guide covers everything you need to know about boiler lockouts.

If you’re experiencing boiler lockout, you’re going to want to solve the problem as quickly as possible. Why? Because until you do, you’ll have no heating or hot water. So, unless you enjoy cold showers and sitting in cold rooms, you need to act fast to figure out what issue is causing your boiler to shut down.

Read on to discover the common causes of a boiler lockout and the steps you need to take to solve it.

What is boiler lockout?

Boiler manufacturers use the term boiler lockout, which essentially means your boiler has shut down due to a fault within your boiler or central heating system. It’s a safety feature designed to protect your boiler and prevent problems from becoming dangerous. So, when your boiler recognises a fault, it goes into lockout mode and stops working.

Many things can cause a boiler lockout, such as power issues, system blockages and faulty components. Boiler lockouts can also occur when too much or too little pressure is in your system. 

How can I identify boiler lockouts?

You probably don’t make a habit of looking at your boiler every day, so the first sign will likely be that you have no heating or hot water in your home.

If you stand in front of your boiler, you might see a red or green flashing light on the display panel. Modern boilers also show a fault or error code, which is usually a number or a combination of letters and numbers, depending on the make and model you have. Fault codes help you identify the cause of the problem and indicate what action you need to take next. 

What should I do when my boiler locks out?

Can you see a fault code on the front display? If you can, you need to determine what the code means. Your boiler manual will include a list of fault codes and explain what they mean and the right course of action.

If you can’t locate your manual, you can check out our guides to fault codes or find the codes for your boiler on your boiler manufacturers’ website.

Once you figure out what the fault code means, you should know whether you’re able to fix the problem yourself or you have to let a professional handle it.

Common boiler lockout causes

Like we said above, many faults can cause boiler lockouts, but some issues are more common than others. You may even find that the fault code on your boiler matches one of the problems below. Let’s take a look at the most common causes of boiler lockouts.

1. High or low pressure

You need to check your boiler manual to determine the correct pressure for your boiler. Most boilers operate at a pressure of around 1.3 bar and will lockout if the pressure is too high or low.

If you notice your boiler pressure is low, you can increase it by adding water via the filling loop. Keep an eye on the pressure after adding water. If it drops again, it could be a sign of a leak somewhere in your central heating system, which will require a Gas Safe registered engineer.

Is the pressure too high? You can reduce it by bleeding your radiator valves with a bleed key.

2. System blockage

Sludge or debris from your heating system can block up your boiler and cause a lockout. Another blockage that can lead to a lockout is a frozen condensate pipe, usually located outside your property.

A Gas Safe registered engineer will need to remove the sludge blockage from your system to get your boiler working again. If the condensate pipe is frozen, you can thaw it yourself using a hot water bottle or heat pack (never use boiling water, though).

3. Pump issue

Pump faults are common and often result in boiler lockouts. Your boiler’s pump can seize up and blow seals or develop a blockage, which will end up reducing the efficiency of your system.

You should never try and sort a faulty pump yourself, so this one is a job for a Gas Safe registered engineer.

4. Faulty fan

A boiler fan problem is never a good thing because it could lead your boiler to become dangerous, hence why your boiler goes into lockout mode when the fan is faulty. All gas boilers need a fully functioning fan to push potentially toxic gases from the boiler to the flue and outside your home.

If a faulty fan is the cause of your boiler lockout, you must call in a Gas Safe registered engineer to repair or replace it.

5. Ignition lockout

An ignition lockout fault code or a flashing light will appear on the boiler after three ignition attempt failures. The exact code will depend on the make and model of the boiler you have installed.

If the problem is an ignition lockout fault, you need to hire a Gas Safe registered engineer to check the ignition leads and flame sensor probes.

6. Heat exchanger blockage

The heat exchanger inside your boiler can develop limescale build-up, which can cause your boiler to make whistling sounds. Also, a limescale build-up on the heat exchanger will result in high water temperatures and a boiler lockout.

A Gas Safe registered engineer will need to look at the heat exchanger, but be aware that repairs can cost are upwards of £500. However, you can expect to pay much less if the problem is dealt with quickly.

If a blockage in the heat exchanger is the issue causing a boiler lockout, you can use a limescale silencer or reducer to help prevent this problem in the future.

7. No power

A blown fuse, tripped electrics, or a faulty display board can trigger a power failure and a boiler lockout. The last thing you want it to be is a fault with the printed circuit board (PCB). Although a faulty PCB is a rare issue, it can be a serious problem and an expensive part to replace.

Should I reset my boiler after a lockout?

If your boiler develops a fault, resetting it is not the answer. You need to identify and fix the problem first. Once you or an engineer fix your boiler, you can reset it.

Modern boilers usually have a reset button on the control panel, which you may have to press once or hold down for a few seconds. You can check your user manual for reset instructions or read our blog on how to reset your boiler.