Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4

Observation:

Check CH control knob is fitted correctly, the control knob should move fully between minimum and maximum however it should not be possible to spin the control knob right around.
Note:
If in doubt or fault has appeared since knob or display board has been replaced then check alignment of the spindle at the potentiometer as it is possible to fit the knob upside down.