RESISTANCE RETURN THERMISTOR

Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4

Set Multimeter to Resistance

Remove the two spade connectors from the return thermistor
This test is easier if access is available on the right side of
the boiler but if needed can be done from inside the appliance

Measurement:

Measure the resistance between the two terminals of the return thermistor.

Resistances vary with temperature and should conform approximately to the table below:

Temperature Range (°C)	Resistance Range
0°C to 10°C	19.0kΩ - 30.0kΩ
10°C to 20°C	12.0kΩ - 19.0kΩ
20°C to 30°C	8.2kΩ - 12.0kΩ
30°C to 40°C	5.6kΩ - 8.2kΩ
40°C to 50°C	3.9kΩ - 5.6kΩ
50°C to 60°C	2.8kΩ - 3.9kΩ
60°C to 70°C	2.0kΩ - 2.8kΩ
70°C to 80°C	1.5kΩ - 2.0kΩ
80°C to 90°C	1.2kΩ - 1.5kΩ
90°C to 100°C	900Ω - 1.2kΩ

Note: Clicking on the resistance table will switch between table and graph view.