Heating choses to work on timer

Hello all.

Moved in to my new house mid Nov 14. Its approx 15yr old Wimpey with a Potterton Suprima 40 boiler and a Boilermate 3.

Initial issues with boiler tripping out appear to be fixed with a new PCB and thermister fitting.

Next issue was stored temp dropping completely down and not returning to set level.
Managed to get work when run timer ON (overide) and putting the 2 position valve into Manual. I have since fitted a new 2 way valve and motorised position valve as old looked/felt a bit tight.

I have left the timer in MID position (timed controlled) and it successfully turned the heating on at the set intervals for the past couple of nights but this morning, it has failed to provide heating for the radiators, although state on the front that the demand is for heating AND store.

Switching the timer to ON position (overide), and heating in radiators then comes on.

Is this highlighting a fault with the timer PCB??
Does the timer PcB control signals to switch the 2 position mototised valve over to provide hot water for heating??

We do have the buzz buzz from time to time from the unit.

Kev

Kind regards

Update:

Since the other mornings failure for heating to start up, I left timer in TOP position (ON) and its controlled the heating okay for a while but then decided to stop heating up.

The only way that I can get the heat to my radiators is by having the 2 way position valve switched into manual position for the boiler to ignite and stay ignited.

Think the heating pump, under this 2 way valve was staying on overnight so think that this is turning into PCB delay timer fault?

Any thoughts or aggreance guys?

Kev