Riello 40 GXB boiler wont fire up?

we have a Riello burner ,which has been recently serviced,new nozzle,new capacitor,typically breaks xmas day in -10 ,we pressed the reset button last time this happened the fan/blower kicked in this time it wont,so my friend took the burner out of the casing and couldnt find anything loose but said the fan seemed quite hard to turn by hand ?? could it be this ?if not what else ??,thanxx