Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Remove plastic cover from the ignition control PCB attached to the gas valve
Move the leads that run to the ignition board
so that the four gas valve terminals are visible
(Do not disconnect any leads)
Selector switch to OFF position
CH temperature selector to minimum
DHW temperature selector to maximum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Selector switch to hot water position.
Allow ignition sequence to commence.
Measure voltage across the live connection of EV2, (the terminal at the top of the four terminals made visible by moving the leads), and connection 2 neutral (blue wire) on the ignition PCB.
Note:
Connections are numbered from the top (1) to the bottom (12).