Set Appliance State:

Mains Power Off
On/Off Switch OFF
DHW Demand - Ensure Store is not up to Temperature
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Appliance On/Off switch On.
Reset lockout as necessary.
Allow fan to run and ignition sequence to commence.
Does the burner ignite and establish?
(Burner establishing is indicated by the "Burner Lit" neon illuminated)