Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove the combustion box door
Disconnect the spark electrode lead from electrode and position the lead such that it is held in place (wedged between the combustion cover and boiler chassis) close to the boiler chassis as illustrated.
WARNING stand clear of boiler whilst test is carried out
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Ensure fan is running.
Can sparking be seen between electrode lead end and boiler chassis ?
Reconnect electrode lead after test complete.