Thermistors are simply clipped on the 'flow' and 'return' pipes. If the pipes are too cold, they may not work properly. I removed them, switched the electrcity supply on and the boiler started to work. Once the pipes had warmed up, switched the boiler off, clipped the thermistors back on and it workded!
The above solution worked by luck than by design. I did initially follow the manual to rectify the 'F10' fault on my glow worm hxi18 but replacing the the 'return thermistor' (around £14) did not help, even though the cables were OK and the contacts between the pipes and the thermistors were OK too.
Hope this helps!
Shaf, December 2009
