Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance

Measurement:

Test 1:
Remove the plug from the gas valve and measure the resistance of the gas valve solenoid between pins 1 and 5.
Resistance should be approx. 4.2Kohm.
Test 2:
Measure the resistance between pin 1 and earth.
Expect a resistance greater than 1 MOhm.