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 if required (rotate selector switch to
'O' position, then rotate back to DHW/CH position).
Allow self-check to complete and boiler to commence its ignition sequence.
At the sparking stage of the ignition sequence measure for
mains voltage across the brown and blue leads of connector X17.
Note.
Appliance may enter lockout during this test, reset as required until test is complete.