Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach pressure gauge to inlet pressure test point
Ensure NO other gas appliances are in operation
NO demands present
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance (if appliance will not reset select that option below).
Allow the appliance to complete its self-check and the burner to ignite and establish and run for CH.
Observe the pressure gauge and remove CH demand to extinguish the flame
(turn CH temperature control to 0 position).
The gauge should return to standing pressure immediately as soon as the demand ceases.