when turning hot water tap on or central heating, boiller kicks in for a prox 15 to 20 seconds then shuts down. it dose this continualy whilst tap is runing or when heating is on.

kev, October 2011

Might be pump stuck, No water circulating in system, so it over heats and shuts down, usually a screw on end of pump, remove that, water will come out, inside, a screwdriver type slot turn it, if moves ok pump free, if not, they can be cleaned, but sort of fiddly. If you not sure. Other than that one of the sensors. Post with more details about boiler, make model etc.

SD, October 2011