Set Appliance State:

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

Measurement:

Test 1:
Measure the resistance between the Blue and Black wires at the connector.
Expect approximately 4.1 KOhms
Test 2:
Measure the Resistance between the Blue wire on the disconnected connector and Earth.
Expected resistance greater than 1 MOhm.
Test 3:
Measure the Resistance between the Black wire on the disconnected connector and Earth.
Expected resistance greater than 1 MOhm.
Note.
A reading of O.L on tests 2 and 3 is acceptable as this is greater than 1 MOhm.