Baxi 105HE Need help please?

Intermittent problem with H/W & C/H. The boiler doesn't fire up when asked 99.9% of the time. Appears the programmers (Digital timer in kitchen and timer on boiler) are working fine. Then it will fire up during a programme period, appearing to be working fine. So we have hot water rarely and central heating rarely.

The fan is working, pressure is at 2bar everything looks correct (I have no experience so would need idiot form information to fix).

thanks