Halstead ace 24 HE combi boiler keeps blowing fuse in PCB?

Every time I try and turn on the boiler the fuse in the PCB blows, the fan runs and on the old occasion and the boiler will fire up for a couple of second and then blow the fuse again. What could be the reason for this?
Pete chalk, April 2014
leak inside boiler getting onto boiler electrics

Q, April 2014
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