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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.

Before we start, if you’re fed up of having an old unreliable boiler, you can get a fixed price online from HEATABLE. Being part owned by Bosch, this is about the best deal you’ll get on a Worcester Bosch boiler.

Worcester Bosch Greenstar i from Heatable

What Is A Boiler Lockout?

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

This could be due to low/high water pressure, lack of or no fuel supply (gas, LPG or oil), a blockage in the system or lack of power to electronic components.

What Happens During A Boiler Lockout?

Expect to see either red or green flashing lights. The boiler will begin to shut down.

Newer boilers with a display panel will display a fault code, which gives an indication of what the problem is.

What To Do When Your Boiler Locks Out

If your experiencing boiler lockouts for the first time, or intermittently, there’s 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 Lockouts

Try to match your fault code to one of the faults below.

We’ve added a quick guideline of the fix needed to clear the fault code and prevent boiler lockouts.

#1 – A Faulty Pump

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

#2 – Ignition Failure

Check the ignition leads and probe. Most boilers lockout after 3 failed ignition attempts.

#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 lockout if they are below 0.6 bar or above 3 bar.

To increase pressure, add water via the boiler filling loop.

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

#4 – No Power

Having no power to a boiler, could be due to a failed display board, a blown fuse, or tripped electrics in your property.

#5 – System Blockage

Especially in the mornings and winter, check your condensate pipe (it vents outside) isn’t frozen.

Other common blockages come from heating sludge build up in 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. It will need to be cleaned.

This will lead to the water temperature getting too high, causing the boiler to lockout.

#7 – Fan Problems

Your boiler’s fan vents gases from your boiler, via the flue. If the fan isn’t working correctly, your boiler is going to be dangerous, and it’s going to lockout.

Step 3: How To Reset A Boiler After A Lockout

Modern boilers will have a reset button on the display button. 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

That all sounds good in theory. But, what if your boiler won’t reset after a lockout? Even when you’ve found and fixed the problem relating to the fault code?

Unfortunately, a boiler’s computing power isn’t like 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 determine if there are any other faults, before resetting again.

#1 – Check 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 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 communicates with all electrical components in the boiler (pump, fan etc) to work.

#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 your property’s electricity hasn’t 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, well, return. Naturally, the water will lose some heat as it travels around radiators and pipes.

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.

What’s Next?

Thanks for reading out 5-minute guide to boiler lockouts. Still not fixed? Checkout our guide to boiler troubleshooting here.

Fed up of your old boiler? Get a brand new Worcester Bosch boiler fitted as soon as tomorrow, from HEATABLE.

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. 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. Not a problem 🙂

  2. 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. Sorry for the delay. Did this get fixed John?

  3. 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. What boiler is it? Any fault code being displayed?

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

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