Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Disconnect X7 plug for outdoor sensor
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now react to a CH demand?
BOILER NOW REACTS TO CH DEMAND
BOILER STILL DOES NOT REACT TO CH DEMAND