Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Disconnect lead from spark generator and position above the generator as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to begin ignition sequence.
Shortly after the fan runs can sparking be seen for approx. 7
seconds between the spark generator and the lead?
Note:
Boiler will attempt ignition 3 times before going to lockout,
with approximately 15 seconds between attempts.
Turn power off & back on to retest as required.