Hi, Although a different type of boiler, this happened to me a few times last summer. In my case it was something to do with the boiler pressure and it seemed to happen when I switched the bathroom hot tap on (not saying yours will be the same) Mine had a reset button although in the end even that didn't help as it continually locked out.
I got a plumber round who told me it was the pressure, funnily enough after doing it half a dozen times it stopped and has never happened since (touch wood). Get yourself a good plumber - i think it cost me twenty quid so not much.



