Set Appliance State:

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

Measurement:

Remove the Black spaded wire and the White spaded wire from the Main Solenoid on the Gas Valve.
Measure the resistance across the Solenoid.
The Resistance across the Solenoid should be approximately 2.1kOhms.