Problem now solved, very simple, a partially block gas injector which was then shutting the boiler down causing the circuit board constantly try try to relight boiler.
Thanks for advice.
I have a problem with my boiler it will not give a constant supply to the radiators, once the room temperture reaches 16 deg C the radiators cool even thou the room thermostat is set to 21 degC, Also the hot water only reaches a warm temperture. All the pipe work and radiators reach very hot...