Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove plug from the operating solenoid. 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.

Measurement:

Test 1:
Measure the resistance across the solenoid coil terminals.
Resistance should be approximately 4 k ohms.
Test 2:
Measure the resistance across either of the
solenoid coil terminals to earth (rear pin).
Resistance should be greater than 1M Ohm.