Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Disconnect the White wire and the Black wire on the Gas Valve Main Solenoid and measure the resistance across the Solenoid Terminals.
The solenoid resistance should be approximately 5.2 KOhms.
Replace leads after test.
The solenoid resistance should be approximately 5.2 KOhms.
Replace leads after test.
Isolate as per TOPs P4
and refit as necessary