Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
DHW Demand
DHW temperature set to MAX
Remove the HT lead from the spark electrode and place close to the top of the heat exchanger as illustrated
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow appliance to go through it's ignition sequence.
Approximately 7 seconds after fan has started is sparking observed at the end of the ignition lead?
Note.
1. Stand well clear of the appliance during the ignition sequence.
2. Appliance may enter lockout during this test, reset as
required until test is complete.