Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Gain access to PCB (use Insulation Mat as required)

Measurement:

Note the initial position of the CH temperature potentiometer
on the control PCB.
Rotate the potentiometer fully clockwise to maximum
and then to fully anticlockwise to minimum.
Turn the potentiometer to approximately 2/3rds
of the potentiometers movement
from minimum to maximum.
Is the position now different
to its initial setting?
Potentiometer position not changed
Potentiometer now in different position - Retest Appliance