Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove electrical connector from right-hand side of boiler
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the wiring to the appliance isolated does the fuse still blow / RCD still trip?
Please choose one of the outcomes below:
FUSE NO LONGER BLOWS / CIRCUIT BREAKER NO LONGER TRIPS
FUSE STILL BLOWS / CIRCUIT BREAKER STILL TRIPS