Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
Remove the black sheathed, grey spark ignition lead from near the top of the ignition PCB
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the appliance to commence its ignition sequence.
WARNING! - STAY CLEAR OF THE IGNITION
UNIT DURING THIS TEST

Does sparking occur across the ignition PCB at the spark connections?
Refit the Spark lead to the PCB connection.