Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Disconnect spark leads from spark generator on PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required (rotate selector switch to
'O' position, then rotate back to DHW/CH position).
Allow self-check to complete and ignition sequence to commence.
Approximately 10 seconds after the fan starts to run can
sparking be seen at the spark generator on the PCB?
Note:
If air flow fault code (70 deg flashing) shows during test click HERE.