Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove PCB Cover
Move the link directly below connector X6 from middle and right pins (Clock) to the left and middle pins (No Clock)
Selector Switch in Heating & Hot Water Position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the appliance now respond to a demand for CH?
Note:
Return link to its original position after test is complete.