You must be specific... Do any lights come on? Is there power to the boiler? What size micro-combi is it?
Could be a billion things, most likely:
+ Stuck Fan
+ Dead PCB
+ No Power
+ OverHeat Tripped
+ Stuck APS
Please contact a registered gas fitter if you cannot be more specific with your appliance... Us gas fitters are not mind-readers.
ccMods, July 2006