Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary.
Observe through boiler sight glass as the boiler
goes through its ignition sequence.
Can the burner be seen to fully crosslight?
Note:
Boiler will attempt to light 3 times before going to ignition lockout (flashing LED).