Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Boiler On/Off switch Off
Pull forward one side of the electrode lead connector
from the control box as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Boiler On/Off switch On.
Reset lockout if necessary.
Allow fan to start, after approximately 10 - 15 seconds does a strong and consistent spark occur between the spark generator and the lead?
Note.
Sparking will last for approximately 5 seconds, then repeats after approximately 15 - 30 seconds, if lockout occurs reset until test is complete.