Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Mode selector switch to Off/Reset position
CH Demand
Central heating temperature control set to maximum
Connect a U-gauge to the burner pressure test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Mode selector switch to CH position.
With a CH demand does the burner ignite on low flame?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.