Glow worm 40ff?

The boiler will not light - when the timer is turned on the mains fuse blows. With the fuse off the timer does light up.
I understand that for the boiler to ignite the timer must be requesting hot water/heating. I did have a water leak in the airing cupboard and water could have sprayed over the mid position acuator (stains on the wall). Could this be the cause of the problem and if so could the problem be the circuit board. To rule this out where can I get a replacement circuit board?