Boiler starts and runs but intermittently shuts down and then immediatly starts up again. lights show boiler on, fan run, pilot and burner when the boiler is operating. when it shuts down the pilot and burner lights go out and the boiler on and fan run lights stay on.
It sits like that for a few seconds and then the pilot and burner light come and it runs for a short period and then goes through the routine again
any help or advice on cause of the problem appreciated