Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Appliance On/Off control set to Off position
Remove one of the wires from the DHW sensor
Appliance On/Off control set to Off position
Remove one of 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 the 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 the test.
Isolate as per TOPs P4
and refit as necessary