Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance as necessary.
Allow the fan to run and ignition sequence to commence.
During the sparking stage of the ignition cycle measure the AC voltage between pins 22 and 23 at connector M7 on the PCB.
Expect mains voltage.
Is the voltage measured as expected?
Note:
Appliance may go to lockout during this test, reset as necessary to confirm result.