ravenheat csi 85a-csi 85at combi boiler?

I have the above mentioned combi boiler, the heating has now stopped working, DHW is running fine. I have noticed that the spindle from the Diverter valve is over to the right hand end of the valve, (looking at it from the front of the boiler, with the cover off).
As,& when I want hot water, it moves to the left to make contact with the micro switch, then starts up to heat the water.
I have taken it off to look for any damage inside it, diaphragm looks fine, springs look OK, small spindles look fine, there was some rust coating the valve seats, but it cleaned off fine without damaging any surface.
Spindles seemed to move through the seal bush's fine.
anyone got any thoughts on this problem?
Page 42 of the manual, fig No: 89
I'm a industrial maintenance fitter, so working with tools and making sure parts fit correctly without any strains or damage is my normal fitting skills.
Thanks for any assistance on this problem. I know its a poor make of boiler but I'm out of work and would love to sort it without major expence.