Probably Hot water sensor needs replacing. Quite a simple job, your boiler instructions will tell you where it is (on the side of the diverter valve).
You need to turn off cold supply to boiler and open hot taps to drain. Turn off electricity, undo wire from sensor (lift small clip on side and pull off) then use a 13mm spanner to undo sensor replace ensure fibre washer is in place
PJ, November 2007
