Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Disconnect the ignition lead from the PCB and with the aid of a crocodile clip position the ignition lead just off the terminal on the PCB (see images)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required.
(Press reset button once then release)
Allow fan to run and ignition sequence to commence.
As the appliance goes through repeated ignition attempts can a strong consistent spark be observed between the ignition lead and the spark generator terminal on the PCB ?
Note.
Appliance may enter lockout during test, reset as necessary until test complete.