Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Selector switch set to CH/DHW position
Boiler DHW thermostat set to MAX
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Observe the burner through the sight glass.
Does the burner ignite and establish correctly?