Boiler repair and servicing

A service is a check, not a clean-out. The engineer reads the flue gases with an analyser, checks the gas rate against the data plate, inspects the heat exchanger, burner and seals, tests the safety devices, and confirms the flue terminal and its clearances. The reading goes on a service record, and on a boiler still under warranty that record is what keeps the warranty valid. Skipping a year to save £90 can cost a £600 heat exchanger.

Most repairs come from a short list of faults. A diverter valve that has stuck gives heating but lukewarm water, or hot water only when the heating is on. A failed expansion vessel shows as pressure that climbs when the boiler fires and drops back overnight. A blocked condensate trap gives a gurgle and a lockout. A pump that has seized after a summer of standing still gives an overheat fault on the first cold morning of the year. Each has a characteristic symptom, which is why an engineer asks about the symptoms before opening the case.

Two faults are worth trying to fix yourself. A condensate pipe that has frozen where it runs outside will lock the boiler out, and pouring warm, not boiling, water along it usually clears it. A boiler showing low pressure needs the filling loop opened until the gauge reads about 1.2 bar cold. If the pressure falls again within days, there is a leak or a failed vessel and that does need an engineer.