swiftflow isn't working?

Swiftflow 75 boiler went off and pilot would not light. Man came - said it was the thermocouple put in a universal which didnt fit so ordered and put in the right (updated) part which doesnt work. (Pilot light lit and gas caught but no heating or hot water - and then went out??)
Man said - after payment - has no idea of what to do next. It's Scotland and cold - any ideas - or failing that what will replace a swiftflow 75 boiler or where to get a swiftflow 75 boiler (s.i.t.)