Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the AC voltage between the Brown and bottom Blue connector at the gas valve during the sparking stage of the ignition cycle.
Expect mains voltage.