Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN2 from the PCB
Remove the electrical connector from the gas valve

Measurement:

Test 1.
Measure the resistance between the brown pin on
connector CN2 to pin 4 on the gas valve connector.
Test 2.
Measure the resistance between the brown pin on
connector CN2 to pin 2 on the gas valve connector.
Test 3.
Measure the resistance between the blue pin on
connector CN2 to pin 1 (blue) on the gas valve connector.
Test 4.
Measure the resistance between the blue pin on
connector CN2 to pin 5 on the gas valve connector.
Expect continuity / zero resistance on each test.
Also visually inspect the condition of the harness.