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View the thread, titled "Glow Worm 30CXI F12 Fault." which is posted in UK Plumbers Forums on UK Plumbers Forums.

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lupieloo

Gas Engineer
Hi

I need help with this fault code F12. Every time i go to the job its on F and then solid red light or F12 and red light. But when i turn it off and on and test it everything works until a few hours later i get a phone call saying its gone to F12 again.

I have in my van the PCB board and display board etc for the boiler but don't want to replace them if they don't need them as if i open them i can't take them back. Is there a way of testing this fault? I seen this on another forum:

F12 fault. This is a communication error between the PCB's. I would suggest taking off the low voltage components as they can cause an interuption on the signal between the boards. These are J1, J4 and J2 on the main pcb. It will then show you another fault. If it shows a fault other than F12 then one of the low voltage components is causing the issue. Its a process of elimination test which means you put one plug on at a time and see which is causing the issue.
If it goes back to F12 when you take these plugs off i would suggest checking the harness to the display which is J13 (5 red wires). If thats ok its most likely an issue with the display board. Sometimes when these boards are changed they do not recognise one another so it can cause issues like this.


[FONT=verdana, arial, helvetica, sans-serif]I Will try this but didn't know if anyone had any other ideas as its a bit hard to find a fault when it starts to work and stay working for abit.
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Any help would be appreciated.
 
Update:

Been out today and found that when I pulled J1 plug out F10 came up. J2 plug out F7 came up and J4 nothing as this is a pressure sensor and glowworm apparently said it wouldn't show anything. Anyway got down to it being the flow switch as the heating was over riding the hot water when you put it in (completely opposite to what it should be) this caused F12. Haven't had a phone call yet saying it's down again so fingers crossed.

Thanks
 
My hunch is flow switch, disconnect the lead at the flow switch and see if its all cruded up.
 
Yes it was a grey one. I've replaced it for the black version. Expensive for what it is £81. Glow worm are terrible but at the end of the day they keep me busy
 
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