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 pins 1 and 3 of the gas valve.
Expect approximately 6.5 KOhms.
Test 2:
Measure the resistance from pin 1 of the gas valve to pin E (Earth).
Expect resistance of 1 MOhm or greater.
Test 3:
Measure the resistance from pin E (Earth) of the gas valve to the pin 3.
Expect resistance of 1 MOhm or greater.
Test 4:
Measure the resistance between pins 3 and 4 of the gas valve.
Expect approximately 0.88 KOhms.