Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance

Measurement:

Remove plug from GV2 this is held in position by a central screw.
To enable ease of access to the screw, remove the solenoid coil from the gas valve, it is held by two screws securing it to the gas valve body.
Measure resistance across the solenoid coil terminals.
Resistance should be approximately 4 k ohms.