Set Appliance State:
Gas On; Pilot On
Set Multimeter to Resistance 
Turn Hot Water Tap On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow appliance to heat DHW to approximately 60°C.
Turn OFF Domestic Hot Water.
Disconnect Red wire from connection 7 on the connector block
(Ensure other end of disconnected wire is connected to the DHW sensor).
Measure resistance between disconnected Red wire and connection 8 (Red wire) on the R/H connector block.
Note: Resistance measured will vary according to the boiler temperature, the cooler the boiler the higher the resistance. The resistance depends on temperature and should conform to the table below:
Turn OFF Domestic Hot Water.
| Isolate Mains Power to appliance as per TOP's P4 |
(Ensure other end of disconnected wire is connected to the DHW sensor).
Measure resistance between disconnected Red wire and connection 8 (Red wire) on the R/H connector block.
Note: Resistance measured will vary according to the boiler temperature, the cooler the boiler the higher the resistance. The resistance depends on temperature and should conform to the table below:
| Temperature °C | Resistance in kOhms |
| 20 - 30 | 12.4 - 7.9 |
| 30 - 40 | 7.9 - 5.2 |
| 40 - 50 | 5.2 - 3.5 |
| 50 - 60 | 3.5 - 2.4 |
| 60 - 70 | 2.4 - 1.7 |
| 70 - 80 | 1.7 - 1.2 |
Isolate as per TOPs P4
and refit as necessary