I've been searching on and off for about 7 years for a solution. It would be OK and the someone would turn the power off and the thing would run and run - and its below our ensuite and would drive me MAD at night :)
Found this on a plumbing forum and worked for my constantly running Worcester Greenstar 30CDi
However, I have discovered if a hot tap is running or if the heating is on (and thermostat set to on) before the boiler is turned on at the mains and then turned off a few seconds after the burners...