Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Expose PCB by removing plastic control box cover.
Remove connector plug D19 / D24 from PCB.

Measurement:

Measure resistance across connections D19 (Orange wire) and D20 (Orange wire) with lockout reset button held in.
Resistance should be short circuit.
Measure resistance across connections D19 (Orange wire) and D20 (Orange wire) with lockout reset button released.
Resistance measured should be open circuit.
Note:
Measurement taken at disconnected plug NOT PCB.