Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Refit case if it was removed previously
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the burner ignite and establish?
Note:
Burner will take approximately 30 seconds to ignite after fan starts and will attempt ignition 5 times before going to lockout.