Set Appliance State:

Mains Power Off
CH Demand
Central Heating Thermostat to Maximum Position
DHW Thermostat to Minimum Position
Ensure Primary Heat Exchanger is cool (40°C or cooler)
Boiler On/Off Switch Off
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Boiler On/Off switch On.
Reset lockout if necessary.
Allow fan to run and ignition sequence to commence.
Does the boiler fire for central Heating?
Note:
If the appliance is too hot and requires cooling down to 40°C or below for the test, run the hot tap with the mains power on to the appliance and the gas turned off.