Set Appliance State:

CH Demand
Isolate Mains Power to appliance as per TOPs P4
CH temperature selector at maximum
Disconnect plug connector ST5 from the PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Appliance On/Off control set to ON position.
Reset lockout as necessary.
With a CH demand does the ignition sequence commence and the burner ignite?