Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Thermostat turned to Max
Refit combustion box door
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Ensure that the Fan is running.
Observing through the combustion door window, does Pilot Ignite?