Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Disconnect the ignition / rectification lead from the back of the PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance lockout as necessary, allow the fan
to run and the ignition sequence to commence.
Is there a strong consistent spark seen at the PCB
from where the lead has been removed?
Note:
The appliance may lockout during this test reset as necessary to complete.