Ferrloi 25c no Heating after new PCB fitted?

Initial fault of F26 caused by frozen condensate pipe. F 26 couldn't be cleared so the PCB had to be changed. After changing PCB the unit ran fine for 18hrs then no Heating but hot water. The pressure did drop due to a leaking pressure relief valve (opened during testing and some debris became trapped) and I suspect that the fault was logged but not displayed and again can't be reset. Has anyone had experience with these (Honeywell) PCB's (part no 39810430) and if they are know to have fault logging problems.
The reset does nothing as there is nothing to reset on the display. When put into test mode the unit functions OK and all radiator heat.

The symptom is almost as if the roomstat is calling for heat but the boiler is not registering. Roomstat has been tested all OK and has even been looped out for testing.

Any help would be appreciated.

Regards Ryan