We have a corgi registered engineer out later today to fit a new electrode plug. He was around the other day and had a look at it. We noticed that one of the plugs kept on generating a spark after the burner was lit, this then cancelled out the burner (maybe a safety switch of some sort) and the burner would then re-light and the same thing happen over and over. Hopefully this will sort it out.
What’s worrying is that there was someone else who had the same problem on here and everyone was saying Micro switch! He had an engineer out and it was the Micro switch. Far be it from me to tell a qualified engineer his job when I know sod all about boilers but it seems a bit of a coincidence to me! Anyway, I'll post on here what the result is and hope it helps others. Cheers
The engineer came out and firstly fitted the new electrode plug, this was not the problem. He then returned and fitted a new PCB and this didn't solve anything either. Finally he came back and fitted a new Microswitch and hey presto it worked!
The advise on this website is spot on and much appreciated.
I watched him fit it and it took about 30 mins all in all. The switch itself is easily disconnected but there are a number of cables (about 5) that need to be wired into the PCB.
All functions seem to be working except the crucial bit.... actually firing up!
I personally have a Vaillant VCW GB 242 EH Boiler so felt quite confident about finding a possible solution. (just about changed every part on it over a 17 year period )
In her boiler I could see what looked like the diverter valve with a rod that moved up and down when either the CH was active or HW was drawn. This microswitch I believe is suppose to trigger the burner?
Looking closely, it seems (microswitch) to be moving freely and a click can be heard when fully depressed.
Is this the likely cause of the boiler not igniting?