Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Ensure the boiler is cool so that there is demand for preheat
Set DHW temperature selector to ECO
Remove both leads from the outlet side of the spark generator
Place the earth lead of the spark generator output close to the spark lead terminal of the generator.
WARNING!!
Keep clear of the lead and generator during this test
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

During the ignition sequence observe the earth lead/ generator terminal.
Is the spark strong and consistent?