Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove control box cover
Disconnect plug marked DHW sensor
(6 way connector with 3 blue leads, 1 white lead and 1 black lead).
Remove control box cover
Disconnect plug marked DHW sensor
(6 way connector with 3 blue leads, 1 white lead and 1 black lead).
Measurement:
Test 1:
With DHW temperature selector set to MAX, measure the resistance across
the blue wire (connection 1) and the black wire (connection 2).
Resistance measured should be approximately 9.5 kOhms.
Turn DHW temperature selector to MIN.
Resistance should reduce to less than 100 Ohms.
Test 2:
With DHW temperature selector set at MIN, measure the resistance across
the white wire (connection 3) and the black wire (connection 2).
Resistance measured should be approximately 9.5 kOhms.
Turn DHW temperature selector to MAX.
Resistance should reduce to less than 100 Ohms.
With DHW temperature selector set to MAX, measure the resistance across
the blue wire (connection 1) and the black wire (connection 2).
Resistance measured should be approximately 9.5 kOhms.
Turn DHW temperature selector to MIN.
Resistance should reduce to less than 100 Ohms.
Test 2:
With DHW temperature selector set at MIN, measure the resistance across
the white wire (connection 3) and the black wire (connection 2).
Resistance measured should be approximately 9.5 kOhms.
Turn DHW temperature selector to MAX.
Resistance should reduce to less than 100 Ohms.
Isolate as per TOPs P4
and refit as necessary