Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Remove ignition electrode and earth lead from combustion chamber and attach to lower L/H side of case

Observation:

Test 1:
Check the ignition electrode gap at the tips of the electrode.
Gap between the electrode tips should be 3mm +2mm/-0mm.
Test 2:
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On
Stand clear of electrode.
Boiler on/off switch ON and allow fan to run and ignition sequence to commence.
After approx. 15 seconds can sparking be seen at the electrode?