Well, obviously I do not know the boiler specifically, but it sounds to me
like a thermal link has blown due to overheating of the transformer. It is
likely that something in the power supply circuit has put a short on the
secondary, or the transformer merely has broken down with shorted turns.
I'd have thought if there had been a fan or other bad component then you
might actually see it or hear it, ie lack of sound if its failed, so short
of trying to get a transformer and replacing the old board, I'd imagine just
checking every so often for overheating might be all one can do.
When this happened to a different appliance here, it turned out to be a
capacitor and a bridge rectifier which had gone, and one could actually
measure this on the old pcb. It was a shame nobody thought to fit a hi tech
device like a fuse in the low voltage side of the ac from the transformer.
grin.
Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Mathew Newton" wrote in message
...
I have an Ideal Icos HE15 heat-only boiler which, by all accounts judging by
plumbing/heating forums on the Internet, appears to be unwanted child of the
boiler world. That said, this one is 12 years old now and has given sterling
performance for the 9 years since we adopted it.

Until now that is. Today the house was cold and the boiler was dead. Many
years ago I'd bought a spare PCB and control panel as I was aware these were
its Achilles heal and, sure enough, replacing the PCB has brought it back to
life.

First thing I noticed with the failed PCB was that the plastic case had a
small area that was dark and slightly warped on the outside:

http://www.newtonnet.co.uk/permanent/icospcb1.jpg
http://www.newtonnet.co.uk/permanent/icospcb2.jpg

Opening up the case revealed that the board looked quite healthy however the
transformer, which is situated right beneath where the warped plastic is,
was a little dark and the label showed signs of what I guess could be heat
stress:

http://www.newtonnet.co.uk/permanent...ansformer1.jpg
http://www.newtonnet.co.uk/permanent...ansformer2.jpg

Measuring the primary coil revealed it was open circuit.

Any ideas what could cause the transformer to fail? Do I dare rejoice that
I've fixed the boiler, only to find out soon (Christmas Day probably) that
there is an external component (e.g. fan?) that might be overloading the
transformer causing it to fail? Or could it just be age / poor design?