Had a plumber round today - still cold - who stated, categorically, that it is the 'PCB board' within the boiler. Basically, I think that is the electronics board within the boiler. Ideal have these on the van but a plumber will wait 2-3 weeks as the boiler is fairly new and bits are not in the re-sale market yet.
I have an Ideal engineer coming round tomorrow.
Hope this helps
Ian
February 2009