How can I fix my worcester bosch 28i?

Hi
My worcester bosch 28i combi boiler packed up(4 yrs old) so I took a look and found fuse 1 had blown. After a couple of blown fuses later I decided to look a bit deeper and found that the fan motor had burnt out.( don't know how ,maybe moisture/condensation) I did some checks and replaced the fan and fuse 1. The fan came on and power was back but I am unable to get the boiler to light.Press the reset and light flashes 4 times/sec which indicates just about anything may be wrong. I have carried out continuity checks and resistance checks as per the installation guide and it all seems to point to the pcb.
Does anyone have any ideas to suggest it may not be the pcb? I'm thinking logically that as the boiler was ok, maybe the fan shorted out and took out the pcb!
When I switch the heating on via the programmer the relay clicks and seems to have a bit of a flash not so sure this is right.
Thanks to anyone who may be able to help.