Have had the same problem for a long time with frequent expensive visits from the 'Plumber'! Had a history of shorting across the pcb and the boiler chassis eventually requiring a pcb change , £400! Probably should have changed the termister as well (what ever that is!) Better but still giving intermittent grief!! Microns have a history regards this type of fault! Check their website for tech info!
Cheers, Tony
Tony, December 2009