i have just had the same problem with my worcester 24i combi boiler, it turned out (a spline that protrudes at the back of the themostat knob had snapped off, probably due to vibration, and it had happened while the stat had been turned down to zero for the summer, when i turned it back up, all appeared normal but the boiler would not strike up, from the information i had at the time, following the fault finding chart in the manual, it led me to believe the pcb was kaput, it is possibble to (turn the power off) and insert a small flat screwdriver in the knob aperture, and turn the stat up to where you want it, as a temporary measure, judging by the hundreds of worcester stat knobs for sale on ebay, its a regular problem, it must be a week point on the machine, a little plastic spline two inches long, not much thicker than a match, fractures by heat and stress of vibration, pull on the knob and it will unclip, check this before you spend 2 or 3 hundred pounds, on a part changing engineer, don't touch anything else before you check this bit, hope this is of use, to someone, it is illegal to repair a gas appliance without a gas certificate, i sorted mine myself, but if you like you can call out and engineer,
STEVEN P,
September 2010
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