Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect X1 (ribbon cable) from main PCB
(this affects resistances and must be done to prevent misdiagnosis)
Gain access to back of display PCB

Measurement:

Test 1:
Set DHW temperature control to maximum.
Measure the resistance between connections 1 and 3 on the display PCB.
Resistance should be less than 10Ω.
Measure the resistance between connections 2 and 3 on the display PCB.
Resistance should be approximately 2.8kΩ.
Test 2:
Set DHW temperature control to minimum.
Measure the resistance between connections 1 and 3 on the display PCB.
Resistance should be approximately 2.8kΩ.
Measure the resistance between connections 2 and 3 on the display PCB.
Resistance should be less than 10Ω.