Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect gas valve electrical connector plug (held by one centre screw) from gas valve

Measurement:

Test 1.
Measure resistance across the two upper pins on the gas valve.
Expected resistance approximately 1.3 KOhms.
Test 2.
Measure resistance across the two lower pins on the gas valve.
Expected resistance approximately 2.8 KOhms.
Reconnect gas valve electrical connector plug after test.