Set Appliance State:

Mains Power Off
Gas On; Pilot On
CH Demand
Rotary Switch in CH and DHW position
CH Operative Thermostat adjusted to Maximum
Keep Boiler Case Switch depressed
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Operate the boiler in its CH mode.
Does the CH flow pipe heat up correctly and do the radiators become warm?