baxi combi 105e boiler,no heating or hot water?

woke up the other morning with no heating or hot water from my 5 or 6 year old baxi 105e combi.i have,within the last 2 months, replaced the central heating temp sensor,and currently have the usual(and sounds like very common)slow drip from the pushrod on the DHW pressure diff valve(cup under the boiler is catching the very occasional drips).the micro switches on the diverter manifold seem to be clicking ok and starting up the fan. though i have noticed that when the boiler is set to hot water only, and i turn the hot water tap on,the push rod for the central heating diff valve raises too,switching the micro switch.not sure if this is supposed to happen or not? the pressure switch connected to the outlet elbow seems to be clicking when i give the tubes a little blow/suck.. the fault lights flashing are the 'flame failure'(30deg) and the 'fault on fan/flue'(50deg).is there anything else i can check before calling in an unknown plummer? i,ve ran out of ideas now.. also got a sparky friend with a meter coming around later today,any advice as to where he should check for me?