Hi Grunff,
Sorry for the delay in replying but my VIA motherboard suddenly took a dislike to my Alcatel modem and the thing had to be changed (motherboard that is)
Back to the subject. It was a Potterton Neataheat wall mounted, balanced flue boiler that was rather old and tired and the pipeworks AND electrics were designed and installed in a new house (the whole site was the same) literally the "wrong way around" thus causing a great many problems - hence the 3 star British Gas maintenance contract - no other firm could sort out the mess.
The Potterton was a nightmare for BG to maintain, at its peak they would be attending at least once a month for a huge variety of problems and it finally gave up the ghost when the cast iron flue rusted away and there were no spares available. A new Baxi Wall mounted boiler cut the call outs down for a few years - but even this has a problem with condensation on the electrode which prevents it igniting now and again - and BG gets the call to fix it.
I quite agree but unfortunately, short of a totally new installation and the mess and upset it causes, I am stuck with what I have got. When I had fairly major problems with silt in the pipes getting BG to flush it out was a damn site cheaper than replacing the system.
Brian