Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Gain access to PCB

Observation:

With the DHW thermostat set to MIN (fully anti clockwise) the small triangular cutout on the potentiometer should be in the 4-5 o’clock position.
With the DHW thermostat set to MAX (fully clockwise) the small triangular cutout on the potentiometer should be in the 7-8 o’clock position.
Does the control knob turn the potentiometer to the correct positions?