problem with boiler

[patchdog]

i have a potterton performa combi boiler which when you have run the hot water tap and turned the tap off the boiler fan and sometimes the burner stays on till you physically turn the boiler off. could this be the pcb at fault?. i would be intrested in any views.
thank you

[gucciman]

possibly but too many people see the pcb as a cure all but in reality they don't fail that often, could well be a sticking diverter valve

[patchdog]

thanks for your answer, a friend of mine also thought that may be the cause as he said they tend to leak after a while but i have checked the operation of the diverter and all seems ok.
thanks for taking time to answer though.