Set Appliance State:
On/Off Switch OFF
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove the wires from the DHW sensor
Remove the wires from the DHW sensor
Measurement:
Measure the resistance across the terminals of the DHW sensor.
The resistance measured will depend upon the boiler temperature, the higher the temperature the lower the resistance.
The resistance should conform to the table below.
Reconnect wires after test.
The resistance measured will depend upon the boiler temperature, the higher the temperature the lower the resistance.
The resistance should conform to the table below.
| Temperature °C | Resistance in kOhms |
| 15-20 | 15.6-14.9 |
| 20-30 | 14.9-10.8 |
| 30-40 | 10.8-6.0 |
| 40-50 | 6.0-4.4 |
| 50-60 | 4.4-3.0 |
| 60-70 | 3.0-2.4 |
| 70-80 | 2.4-1.6 |
Reconnect wires after test.
Isolate as per TOPs P4
and refit as necessary