raden wrote:
In message , Joe
writes

So this looks like a flame-failure device fault. Does anyone know
whether this is purely thermo-mechanical, or whether it's an electric
valve and sensor? The latter would seem to imply that the computer
crash was the result of a dodgy joint, and it might be worth reseating
everything. I would assume if it's purely mechanical then it needs
replacing.


It's not a computer, it's a very naughty boy

That's why it's called junior

the 28i Jnr uses purely electronic sensing, nothing magic about that,
the pcb just detects a small rectified current from the flame

Now, this is where it gets embarrassing ...

I'm the boiler pcb expert and I have a W-B 28i Jnr, and I can't remember
whether the pcb senses the flame over the HT lead or a separate sensing
lead, I think the latter (It will be in the manual, which I am too lazy
to go and check)

Sources of flame sense failure are

1) pcb fault (prolly not much you can do about tis unless you are fairly
clued up, engineer or not) the 28i Jnr isn't so prone to cracked solder
joiints, but worth checking around the HT transformer area

2) Broken flame sensing lead

3) Flame sense electrode not in the flame

4) earthing problems - without a good earth, flame sensing will fail


Thanks for your time. I can expect The Man to tell me I need a new PCB,
then. I'll have a quick look at any accessible wiring and connectors,
but I have no interest in dismantling anything with a seal.