Main 24 HE Combi Boiler strange behaviour

9 Apr 2022
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United Kingdom
I'm looking for help with strange behaviour from a Main 24 HE Combi Boiler.

Symptoms are when turning the boiler on regardless of either heat & DHW or just DWH are after 5 secs the lights show:
Burner light is off
Flame failure light is flashing slowly
Power on is on

The boiler won't fire.

However, if a call for heat or DHW is made at the same time as turning on the boiler it fires up and works until the call for heat is stopped and then the above lights show again and the boiler will not fire.

I have had a Baxi engineer look at the boiler but he couldn't figure out the issue, he changed the pcb, diverter valve and pressure differential assembly.

Thanks in advance for any thoughts on this.

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If it’s the same as this (photo) then suspect the pressure or circulating pump.

@gas112 or @ianmcd might be able to confirm this.


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Hi Chris,
Thanks for your reply, the system pressure is good and I suggested a pump issue to the Baxi engineer after looking at the same troubleshooting page as you. He dismissed it as the heating works if there is a call for heat when the boiler is first switched on.
However, the call for heat then extinguishes and you get loss of flame, after 5 seconds?
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So, how do you reset it, or do you not? It might just be a case if fixing that then?
ok let me try again with this link video
I turn the boiler off and on and provided there is a call for heat it will work until that call stops
That is odd behaviour. I’m surprised with the Baxi engineer though. I would be tempted to look at the flame signalling (rectification). This isn’t a diy job though.
very strange one would need to be in it to see what the hell its doing , possible loom fault . Did he change the sensors as they can throw up strange faults on these
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Disconnect the wire to the condensate trap and see if that affects what's happening.
in your video to reset you are turning the control kno to O dont do this, when the flame failure light comes on, turn and hold the control knob to the "reset" position, hold in that position for about 15 seconds then release, does this make any difference ?
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