Set Appliance State:

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:

Allow fan purge to complete (2 minutes).
Allow fan to run and ignition sequence to commence.
Measure the AC voltage between connector X12 and a suitable earth during the ignition sequence.
During the ignition cycle the voltage will drop from 210 vac to approximately 190 vac or below as sparking takes place, it should then increase again as soon as the burner ignites to approximately 199 - 203 vac.
Does the voltage behave as described above?
Note:
This test may need to be repeated several times to confirm the result, if the appliance locks out reset as necessary.