Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Measurement:
Remove both the 4 way plug from the PCB and the plug from the gas valve.
Measure the resistance of the red and black wires.
Also check the condition of the harness visually.
Expect continuity / zero resistance on each test.
Are the resistances as expected and is the harness in good condition?
Measure the resistance of the red and black wires.
Also check the condition of the harness visually.
Expect continuity / zero resistance on each test.
Are the resistances as expected and is the harness in good condition?
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Isolate as per TOPs P4
and refit as necessary