Set Appliance State:

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

Measurement:

Test 1:
Measure the resistance between the pins of the gas valve.
Expect approximately 85 ohms.
Test 2:
Measure the resistance from the top pin of the gas valve to earth.
Expect Open Circuit.
Test 3:
Measure the resistance from the bottom pin of the gas valve to earth.
Expect Open Circuit.