Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Gain access inner combustion chamber
Fit APS test kit to left hand connection on APS (tube that runs to venturi)
Ensure pressure reads zero before turning power on
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Once fan has started to run increase the pressure via
the APS testing kit to approximately 2mbar.
Can sparking now be seen at the electrode?
Note:
Syringe will only need to be pushed in slightly to
reach 2mb, take care not to overpressurise.