Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove inner casing cover
CH potentiometer set to minimum
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if it is in lockout.
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 and will make 5 attempts at ignition before lockout will occur. This can be reset by pressing and holding the reset button (flashing) for a few seconds.