Combi 80 Central heating off, summer use of hot water only. Boiler static,power on, when extract fan starts short gas burning period, then flame cuts out but fan continues to run. The fan stops after an extended period of running without intervention. If the hot tap is opened after such an incident the water is almost boiling. Central heating switched off. Switch off boiler and fan stops, switch on the boiler and the fan starts. Lot of head scratching!

Des T., August 2008

If the boiler fires up when the heating is switched off and no hot tap is running the problem is that the hot water flow switch is stuck on or is faulty. This can be confirmed by disconnecting one of the wires to the switch which should stop the boiler

Ian, September 2008