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)
Using a crocodile clip attach the ignition lead so the end is just above the spark generator terminal as shown
(no greater than 4mm away)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance lockout as necessary, allow fan purge to complete (2 minutes), allow the fan to run and the ignition sequence to commence.
Is there a strong consistent spark between the spark generators terminal and the end of the ignition lead?
Notes:
1. The ignition lead may differ in appearance but the test is carried out in the same way.
2. The appliance may lockout during this test reset as necessary to complete the test.