You probably have a water leak in the system somewhere that is causing a demand for heat. I have a potterton 100 combi and this was the cause of a similar problem.
Check all taps are off and not leaking and check all water pipe connections on boiler arent leaking.
CJ
March 2007
I can answer this question...
potterton combi 100 overheat kees trip when turn tap off.burner on/off ok?
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