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