geoff wrote:
It certainly seems to be the first thing to look at

If you are confident enough with electricity, you could try connecting
it up to the mains (via a plug with a 5A fuse in (unless you like big
bangs))

If it blows the fuse, you've found your problem

OK, firstly I now appear to have blown the PCB, tested last night without
pump connected and all was OK, switched off, connected pump, switched on and
there was a pop, noticed fuse on PCB had blown so replaced and even without
pump conncted this time there was no light indicating Boiler ON, removed PCB
and there is a small burn mark towards rear around two resistors, so I'll be
needing a recon replacement from you for starters! (Baxi Part: 231711).

As for the pump, disconnected, attached plug (with 5A fuse) and connected to
mains, as soon as it is switched on the master trip in the CU activates
although the 5A fuse does not blow! This obvioulsy suggests the pump has a
problem but my electrical knowledge is not good enough to explain why the
fuse remains intact. The good news is there are valves directly above and
below the pump so a full system drain is not necessary.

Would you agree that the pump appears to have been the culprit here? I'll
source a new replacement, it's a Grundfos Selectric UPS 15-50 and hopefully
this should be relatively simple to replace. As for the PCB, I'll contact
you directly regards a replacement.

--
Darren