My Potterton Netaheat boiler won't work?

The time controller in the kitchen will work when electric is switch on, both HW and HTG are put to the on position.

I attempt to turn the boiler on and the fuse blow in the plug for the time controller. ?

Have disconnected the fan, done the same as above but the fuse does not blow this time. Taken the fan off, connected it to the mains and its works ok ?