Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove the mains supply to the appliance from outgoing side of
the terminal strip (TO PCB) and make safe (left 3 terminals)
Replace mains fuse
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Does the mains power supply to the system establish or does the mains fuse blow again?