Can anyone help with this one? i went out to the boiler and found that it was leaking water and the pcb fuse had blown, leak was from the auto air vent. replaced the fuse and it blew again straight away. unplugged the fan and it would power up. i replaced the fan, harness and the air vent. boiler powered up normally and ran for an hour. it then blew the fuse again. any ideas? i could umderstand it being a pcb problem ,but im confused as to why it would run for so long.