Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Lift one spark electrode lead approx. 5mm away from the spade connection as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Shortly after the fan begins to run
can sparking be observed at the PCB?