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 attach the ignition lead to the PCB cover (see image)
(Ignition lead positioned just off the terminal on the PCB)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Cancel purge cycle.
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 ?