Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to AC Volts Set meter to measure AC Volts
Unplug ignition PCB 22 from main PCB 23
Attach +ve probe of multimeter via crocodile clip to pin 1
(this is the pin furthest to the left of the exposed pins where the
ignition PCB was connected) ensuring that the metal parts of the clip
do not touch any other pin
Mains Power On

Measurement:

Measure voltage across pin 1 and the neutral (blue wire)
on the 11 connector terminal block on main PCB 23.
Mains power OFF.
Replace ignition PCB 22 after test.
WARNING!
This test requires a mains voltage reading taken at exposed pins - care must be taken.