Set Appliance State:

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

Measurement:

Test 1.
Measure resistance across the two upper pins on the gas valve. Expected resistance approximately 17 Ohms.
Test 2.
Measure resistance across the two lower pins on the gas valve. Expected resistance approximately 33 Ohms.
Refit connector after test