I have had British Gas out three times in a week. Same problem...
They fitted the water pump
Thermacouple...
New ignition and an electrode...
Your pump has backed up therefore your boiler cannot switch back to the Central Heating part and because its running on the hot water side, it is over heating and therefore the pilot light is being extinguished as a safety cut off.
Word of warning. The first engineer came out and lit it with his cigarette lighter and left me with it... my partner removed the cover and confirmed my conclusion as there was no "spark" so how did he light it...
The second engineer much more helpful, replaced all of the above... however I have a carbon monoxide leak now and am unable to live in my home. Am awaiting a call to say he can find a new casement for the boiler, if not that sheet of metal which has buckled will now cost me £2-£5K to replace... so watch these enginners like hawks!! British Gas employ cow boys too sadly! The Carbon Monoxide has been escaping for years and not one of them picked up on it!!! They have been servicing it etc and saying it is safe! I'm lucky we wake in the mornings!
S Quinn
January 2010