How can I fix my Baxi Solo 3 PFL 40?

Baxi Solo 3 PFL 40 connected to Boilermate 2000 system.No hot water or heating,no hot water stored in Boilermate but lights on & appears to be working - checked fuses, sensors & no obvious burns on pcb so would appear it's not being supplied by the Baxi.Baxi has no lights on, checked power supply, fuses & pcb (which was replaced few months ago).Potentiometer also seems to be working. However, when checking wiring, discovered that system works when wire from switch live connected to permanent live! Have put separate connection between the two & got hot water & heating but still not sure what the fault is, how to sort it properly & if temporary repair a safe one!Can anyone help?