Are you experiencing boiler ‘lockout’ but aren’t quite sure what it means or what’s causing it?

It can be particularly worrisome when your boiler ‘locks out’ – especially in the colder months when you need it the most.

Having helped many customers over the years and troubleshooting many faulty boilers, I know that boiler lockout is particularly common in older boilers – but it can happen in newer ones, too.

Below, I’m going to tell you a bit more about boiler lockout, it’s causes, and the steps you should take when experiencing this problem.

What is boiler lockout?

Boiler lockout is a term used by boiler manufacturers, and means that the boiler has shut down, due to not having the correct parameters to run. This could be down to a simple glitch or power cut, low pressure, or a more serious safety issue.

Usually there is a reset button on the front of your boiler, and your instruction manual will tell you to press this in order to reset the boiler to stop the lockout.

What happens when a boiler ‘locks out’?

When a boiler locks out, it stops working and the display unit will flash up with an error code to inform you of the fault.

Your boiler may need to be reset for any number of reasons. Sometimes the problem can be fairly obvious, such as if there’s been a power cut. Low pressure will show the pressure gauge at below one bar.

If in doubt, check your boiler’s manual for more information on the various fault codes and diagnostics.

I’ve put together the below guide of the steps you should take when you experience boiler lockout:

Step 1: Check the boiler’s pressure

If your boiler’s pressure has fallen below one bar, it means that your boiler’s pressure needs to be topped up. This is not a particularly serious problem, and you should be able to reset the boiler once the pressure is back to normal.

However, you should bear in mind that this problem may only get worse and more frequent with time, and I’d recommend getting an engineer to look at it before it causes any further issues with your boiler.

Step 2: Check the power

Take a look to see if there is power to the boiler, and that the boiler display is showing. Perhaps a fuse has blown or someone turned off the fused spur (power switch) causing your boiler to turn off.

Step 3: Check the radiators

If your boiler comes on for a short period, and then locks out again, check to see if the radiators are warming up, or if the boiler is just getting hot and then stopping. Knowing the answer to this will save time when you call an engineer.

Step 4: Press the reset button

Press the reset button and see what happens next. Does the boiler fire back into life, or does it refuse to co-operate? In a lot of cases, you’ll find resetting the boiler does help fix the problem.

However, if you are having to reset your boiler two or three times, there will be a good reason for doing so. Always call a Gas Safe registered engineer and get it checked out, just in case. It could be a safety issue.

Step 5: Check the fault code

If your boiler continues to lock out, you will usually see a fault code appearing in the display. Take a note of all or any fault codes that have appeared during this process, and check them in your boiler’s manual or online.

When you call an engineer and give this information, it will save time and give the engineer an idea of what to expect in advance. They may even have experience with this particular fault and be able to give you some quick advice.

Once I was called out to a Potterton boiler that was displaying known fault codes indicating there was a fault in the circuit board. I talked this through with the customer on the phone, including how they’d tried to reset it, and getting them to check the boiler model.

We’d actually come across this same issue a number times, so we were able to pick up the part and replace it right away, saving time on a double visit. It also saved the client some time without heating and hot water, so everyone was happy.


If you’re having trouble with boiler lockout, it can be particularly annoying and worrisome, as it means you’re boiler has stopped working and needs to be reset.

Boiler lockout can be caused by a simple glitch or power cut, low pressure, or a more serious safety issue. If you experience boiler lockout more than once or twice, you should get it checked out by a professional engineer.

If you experience boiler lockout, you should:

Step 1: Check the boiler’s pressure

Step 2: Check the power

Step 3: Check the radiators

Step 4: Press the reset button

Step 5: Check the fault code

Checking all of these things will help you determine the problem and explain the situation to a Gas Safe registered engineer, who will be able to help you.

Remember, reset once or twice at most, be safe, don’t try to fix it yourself and call in an experienced, professional heating engineer.