Greenstar RI boiler not working?

We have a WB Greenstar RI boiler that is about 7 years old and has run pretty faultlessly in that time. It has been serviced twice since installation and admittedely the latest period prior to breakdown has been the longest without routine service being undertaken. That said, we have had a qualified Gas Safe engineer out to look at the boiler and despite giving it a full service, checking the pump, replacing and checking fan assembly, replacing PC board with two (!) alternative new ones the boiler is still inoperative. In trying his very best to repair our boiler our engineer has spoken on four occasions over the phone with Worcester Bosch technical staff who have not been that helpful and we are now in the position where after a week without heating or hot water the only option is to call out a WB engineer to come and scratch his head as well. This will cost us £265 (paid up-front) for the privilege and they are currently quoting a 5-7 day waiting period. Before we commit ourselves can anyone else out there offer any ideas? Thanks.