Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove inner casing cover
Selector switch in DHW position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan to run.
Can sparking be observed between the two spark electrodes situated at the front L/H side of the burner?
Note:
Sparking will only be present for approximately 10 seconds, with no burner ignition lockout should occur. This can be reset by switching the mains power supply to the appliance OFF and ON again.