Set Appliance State:

Gas Off
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Disconnect the middle wire from the ignition electrodes
Remove cover from the PCB housing
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Shortly after the fan begins to run sparking should be observed on the underside of the ignition PCB near the top of connector CN1.
Is sparking present?
Note:
After 5 attempts the boiler will go to lockout. To reset the boiler switch the boiler On/Off switch Off then back On.
Sparking present
Sparking absent