Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect lead from gas valve
Measurement:
Check for continuity (zero resistance) on each of the wires between the gas valve and the PCB:
Grey to Grey,
Black to Black,
Red to Red,
Violet to Violet
Also carry out a visual inspection of the harness between the gas valve and the PCB.
Grey to Grey,
Black to Black,
Red to Red,
Violet to Violet
Also carry out a visual inspection of the harness between the gas valve and the PCB.
Isolate as per TOPs P4
and refit as necessary