I have a Worcester-Bosch 28iRSF. Having not used heating for many months, recently switched on and blew the fuse. Having replaced appropriate fuses, the hot water is working but switching to heating immediately blows the fuse again. I have hand-cranked pump in case it was stuck but to no avail. Wiring appears okay but haven't been able to do full electrical testing. Instruction booklet suggest replacing PCB but I'm not convinced yet - any ideas on other tests I need to carry out?

Dave Halliday, October 2006

Pump not used during hw demand..Try disconnecting pump from elecs for few seconds in ch demand to prove (beware of overheating)

Kev, November 2006