Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector from gas valve

Measurement:

Test 1.
Measure for resistance across the outer terminals of the gas valve.
Expected resistance approximately 4.1 Kohms.
Test 2.
Measure for resistance across one of the outer terminals to the center terminal of the gas valve.
Expected resistance greater than 1 Mohm.
Note.
Ensure a good connection is made or misdiagnosis will occur.