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The Causes Of Boiler Lockouts, And What To Do Next

Are boiler lockouts causing you grief? No problem. In our 5-minute guide, we’ll cover what a boiler lockout is, what happens during a lockout, and what to do next.

boiler lockout causes


What Does Lockout Mean on a Boiler?

A boiler lockout is a safety feature that initiates a shut-down procedure when a boiler is not working within certain tolerances.

Boilers can lock out due to various problems, such as low/high water pressure, lack of, or no fuel supply (gas, LPG or oil), a blockage in the system, or the lack of power to electronic components.

What Happens During Boiler Lockouts?

Though the lockout process varies between boiler manufacturers, you can expect to see either red or green flashing lights, and the boiler will begin to shut down.

Newer boilers with a display panel will show a fault code, which should give you an indication of what the problem is.

What to Do When Your Boiler Locks Out

If you’re experiencing boiler lockouts for the first time, or intermittently, there are a few things you can do.

Step 1: Determine What the Fault Code Means

Alongside flashing lights on the display panel, you’ll notice a fault code.

Take note of the fault code, and reference your owner’s manual to determine what the code means.

Step 2: Find and Fix the Fault

Resetting your boiler at this stage will do nothing. You need to fix the problem before going any further.

Common Faults That Lead to Boiler Lockouts

Try to match your fault code to one of the faults below. We’ve outlined solutions for clearing these fault codes and preventing boiler lockouts.

#1 – A Faulty Pump

Pumps can blow seals and seize. If your fault code relates to pump failures, or water circulation, read our article on fixing boiler pump problems.

#2 – Ignition Lockout

If you experience an ignition lockout, your boiler has probably attempted to fire up 3 times — and failed. If this happens, you’ll see an ignition lockout fault on the boiler’s display.

Ignition lockout fault codes depend on the brand and model. For instance, an ignition lockout on an Ideal boiler triggers the L2 error, whereas a Worcester would respond with a slowly flashing light and a flashing lockout reset button.

If you’re getting an ignition lockout fault from your boiler, call a Gas Safe engineer or your boiler care plan provider and request an emergency assessment of your boiler. The technician should be able to check the ignition leads and probe to establish whether they’re the issue.

You can also learn more about ignition lockout faults in our thorough guide here.

#3 – Low/High Water Pressure

Reference your owner’s manual to determine the pressure your boiler should operate at.

1.3 bar is normal, and most boilers will lock out if they are below 0.6 bar, or above 3 bar.

To increase pressure, add water via the boiler filling loop. But keep in mind that a loss in pressure typically means a leak affecting the boiler or the central heating system, and you’ll have to fix this leak first.

To reduce water pressure, bleed radiator valves with a bleed key.

#4 – No Power

Getting no power to a boiler is a common lockout cause that could be due to a failed display board, a blown fuse, or tripped electrics in your property.

#5 – System Blockage

Make sure your condensate pipe isn’t frozen, especially on chilly mornings and during winter.

Other common blockages come from heating sludge buildup in the radiators and pipework.

#6 – Heat Exchanger Blockage

If you’ve noticed a whistling noise coming from your boiler, there’s a good chance there’s limescale build up on the heat exchanger. This buildup will cause excessively high water temperatures, and your boiler will lock out.

#7 – Fan Problems

Your boiler’s fan vents gases from your boiler via the flue. If the fan isn’t working correctly, it’ll be dangerous for your boiler to operate and it’s going to lock out.

Step 3: How To Reset a Boiler After a Lockout

Modern boilers have a reset button on the display button. Once you’ve resolved the underlying issue, simply press and hold the button to reset the boiler after a lockout.

For older boilers (or boilers that don’t have a reset button on the front of the boiler) refer to the manual to determine the reset procedure.

Step 4: What to Do if Your Boiler’s Locked Out and Won’t Reset

But what if your boiler won’t reset after a lockout, even after you’ve fixed the problem relating to the fault code?

Unfortunately, a boiler’s computing power isn’t like that of a PC or laptop. It will try and determine the most relevant fault code. But, that doesn’t mean it’s correct, or the only fault with the system.

So, you’ll need to run through some checks to find other potential faults before resetting again.

#1 – Check If the Pump Is Working

Can you feel small vibrations and humming from the pump? This signals the motor is working.

If it is, is it too hot to touch? A hot pump suggests seized internal parts. A gentle tap can sometimes free them.

#2 – Adjust Boiler Pressure

The pressure on your boiler should be 1.3-1.5 bar. If it’s not, this could cause a lockout.

#3 – Determine if the PCB Is Working

The PCB (Printed Circuit Board) is the heart of a boiler. Is the display panel showing any lights or codes, or is it completely blank?

A boiler will immediately lockout without a working PCB, as this unit facilitates communication between all electrical components of the boiler.

#4 – Check for Power

Check the condition of the fuse. If the fuse hasn’t blown, try plugging in the boiler elsewhere. And, of course, check to see if your property’s electricity has tripped.

#5 – Monitor Heat Flow

There’s a flow and return water pipe on each boiler. One should be piping hot, the other slightly cooler.

Flow is the hot water leaving the system; it travels around, and returns via the return. Naturally, the water will lose some heat as it travels around radiators and pipes; but it shouldn’t be exactly cold.

If the flow is hot, but the return is cold, that’s a sign of a blockage. Most likely, it’s limescale and heating sludge that needs to be removed with a power flush.

Boiler Still Won’t Work?

Does your old boiler keep locking out despite repairs? If so, it may be time to consider investing money in boiler replacement.

You can start by getting a fixed-price online quote from Heatable — they typically have excellent deals available on top boiler brands, such as Worcester Bosch, Viessmann, Ideal, and others. All you have to do is fill out their anonymous questionnaire about your existing central heating system, and you’ll get a range of boiler recommendations, along with installation quotes. Then, you can use Heatable’s quote as a benchmark when you call your local boiler installers — this will raise your chances of finding a good boiler deal.

Heatable boiler installations

What’s Next?

Thanks for reading out 5-minute guide to boiler lockouts.

Still haven’t fixed yours? Check out our guide to boiler troubleshooting here.

Still have a boiler that is locking out, and have questions? Drop a comment below and we’ll get back to you as soon as possible.


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  1. Mervyn Pitchford says:

    Thanks for the info . A trip up the ladder with a kettle of hot water sorted it on one of the coldest days this winter.

    1. heatingforce says:

      Not a problem 🙂

  2. John kennedy says:

    We have a Worcester greenstar 301 combi boiler 2 years old.. No heating now for 2 days can’t get engineer till Thursday-fault code EA 227 Ignition / Ionization fault – should I cut condensation pipe?? Getting desperate as got young children in house freezing
    Thanks in advance

    1. heatingforce says:

      Sorry for the delay. Did this get fixed John?

  3. Lynne Slator says:

    Having read all of your summery on boiler lockout l am still without heating and hot water.l think the system is quite old so l only have a red light .l keep pressing the reset button and l can hear the boiler sparking up but it is only boosting for a minuet or two and then it locks out again .do l need to do any thing else to try to keep the boiler working? This has been like this for 4 days now ! Many thanks Lynne Slator.

    1. heatingforce says:

      What boiler is it? Any fault code being displayed?

  4. David Rankin says:

    Having read all of your summery on boiler lockout l am still without heating and hot water.l think the system is quite old so l only have a red light .l keep pressing the reset button and l can hear the boiler sparking up but it is only boosting for a minuet or two and then it locks out again .do l need to do any thing else to try to keep the boiler working?
    No fault codes as its the one with just a red reset button in the middle.. it also has no drop down cover on the front… any ideas

    1. Alex Ion says:

      Hi David, if you do end up deciding it’s time for a new boiler you may want to take the Worcester Bosch deal from BOXT – I think they are the best in the market: 10yrs warranty and installation in 24hrs.

  5. Tracey french says:

    Vokera Unica i32 boiler 4 years old. Vokera been out numerous times over the past 18 months same fault code A07 which says thermistor or circulation problems.
    Vokera changed thermistor then it went again on the hot water side changed again.Then did a water test through Fernox who said the system needed a cleaner F5 and more inhibitor putting in. Boiler then same fault code again but works if \I put the underfloor heating on first for 10 mins before then switching on the radiator side of the house then the system runs Ok as long as the temp control on boiler for rad temp is not turned up and left on low. Took Vokera advice and have had system powerflushed with Fernox cleaners and now it is worse. Boiler works on the underfloor side but as soon as the timer comes on for the radiator side of the house it locks out and I have to keep resetting until it comes on. When it does some rads get really hot quickly but I have 2 on the end of the run that one gets luke warm and the other stays cold. They have been bled system balanced but no difference. Vokera will not come out as say it is not a boiler fault in their opinion. Help don’t know what to do next

    1. Alex Ion says:

      I think you’re having a system/pipe problem in there. An engineer who knows his business should be able to fix this for you and figure out where the loss is coming from. Check the links above for local engineers who can get things done.

  6. Robert G Williams says:

    My Greenstar Danesmoor 18725kW has started locking out. When re setting it ignites but the second burn will not restart the boiler. My service engineer has replaced the oil pump but it is now worse. What is the matter with it? What has to be done to get it to run normally?

    1. Alex Ion says:

      Hi Robert, it may be that this is beyond repair. An engineer who knows his stuff should know what to propose.

  7. Ian Souch says:

    Hi, I have a Worcester 37CDi Greenstar. It locks out intermittently EA is displayed. 18 months ago I replaced electrode assembly because the ionisation probe had worn away. That solved the problem for months but now it’s back. When I the probes they are covered in a slight yellow film. When cleaned up all is good for a while.
    At the start of lock down I cleaned out the heat exchanger using the Worcester cleaning tools & fitted the new gasket. I also cleaned out the trap & refilled with water.
    Would you recommend fitting new electrodes or do the settings need adjusting to improve combustion?
    Boilers probably 9 years old.

  8. Alan says:

    Hi I have a ideal boiler which is saying ignition lock out but no other fault code I’ve drained the system put everything back on worked great piping hot water and hot radiators.I turned off the heating and an hour later water was cold and boiler locked out again any ideas what to try next

  9. Chris says:

    I live in a hard water area have a 9 yr old Greenstar Junior 24i
    It has previously cut out and adding water to bring the pressure has fixed the problem after resetting.
    Have just try the heating for first time after the long summer and it locks out after 3 abortive attempte to ignite. Slow red flashing light and same for blue light. I adjusted water pressure to 1.5 bar but resetting does nothing.
    The boiler still works for hot water.

  10. Daniel says:

    we have an old fashioned international brand hot water heating system pilot light stays lit but main burner won’t light how can we fix this

  11. Glenn Brown says:

    My boiler stopped working over Xmas !!!! No display, I had 240v going into the boiler. I changed both PCB’s and thought I had cracked it. The Boiler came on but with an error code F0 which was no BCC chip card, I then order one, installed it but that put me back to square one. No power or display, but i still have 240v going into the boiler. No heating for the last 11 days and the struggling to figure out what it is. I would call a plumber but since I have not worked because of covid, there is no way i can afford to pay. Kind Regard Glenn

  12. Karen Blacklaw says:

    I have a firebird oil boiler 4 yrs old,I have been having a problem with a error 05 for the last 2 yrs, I’ve replaced the pump, digital control box and the photocell my tank has been emptied to make sure there’s no water in it,a filter was put in to make sure there’s no air in the system but still a error 05 so I need to reset it frequently,it can cut out daily,weekly or monthly there’s no pattern, now I’ve had enough and hoping any advice would be much appreciated

  13. TrevorC says:

    Hi, An interesting article – but!
    I get the lockout error every morning with my Ideal Logic+ Combi (installed 2017). The fault finder in the manual seems to assume only two possible options. If I press reset the boiler it will either not start or start and then go off. But when I press the reset button it starts fine and runs. If there is a problem why would it do that? Gas and water pressures are good.
    If I set the timer so that the boiler is on continuously and manually turn the central heating temp down at night, so the heating is not running – no problem. It only has a problem when it is on a timer and tries to restart after being off at night. But then I press reset and its ok. Its just a pain going to the garage every morning to restart it!

  14. B. Hunter says:

    Having read all of your summery on boiler lockout l am still without heating and hot water.l think the system is quite old so l only have a red light .l keep pressing the reset button and l can hear the boiler sparking up but it is only boosting for a minuet or two and then it locks out again .do l need to do any thing else to try to keep the boiler working?
    No fault codes as its the one with just a red reset button in the middle.. it also has no drop down cover on the front… any ideas. The boiler is only 12months old

  15. Caroline Surtees says:

    My gas boiler goes on lockout frequently but will start when direction followed. It seems to do this when the weather starts to be colder and has been doing this for several months now. Is it a problem for an electrician or a plumber? It is about 10 years old but has been doing this for several years and the plumber has checked it over this time but it never helps …

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