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 4 of the gas valve.
Expect approximately 6.5 KOhms.
Test 2:
Measure the resistance between pins 4 and 5 of the gas valve.
Expect approximately 0.88 KOhms (880 ohms).
Test 3:
Measure the resistance between pins 3 & 4 of the gas valve.
Expected resistance greater than 1Mohm.