Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure AC voltage across brown and blue terminals on the 7 way
connector on the left of the Ignition board at positions 4 & 5.
Expect mains voltage.
Note:
Voltage will only be present during the sparking phase of the ignition sequence.