Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector from gas valve

Measurement:

Test 1. Measure for resistance across pins 1 and 5 of the gas valve.
Expected resistance 4.2 kOhms.
Test 2. Measure for resistance across pin 1 gas valve and Earth
(Main terminal block).
Expected resistance Open Circuit.
Test 3. Measure for resistance across pin 5 gas valve and Earth
(Main terminal block).
Expected resistance Open Circuit.