Set Appliance State:
Mains Power Off
Set Multimeter to AC Voltage 
CH/HW switch in HW position
Ensure that the boiler is cold and ready for Pre-heat
Boiler On/Off switch ON
Ensure that the boiler is cold and ready for Pre-heat
Boiler On/Off switch ON
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure mains voltage across gas valve 2
(main gas valve solenoid) white (Live) wire
and blue (Neutral) wire.
(main gas valve solenoid) white (Live) wire
and blue (Neutral) wire.
Isolate as per TOPs P4
and refit as necessary