Ecodan Thermistor Specifications


I want to install a therminstor in my Ecodan connecting it to CN20 connector.

I have been looking for the technical specs of such thermistor but I didn’t find anything.

Any idea about the tech specs for the thermistor (TH1)? NTC or PTC? Resistence?

I tried a NTC 10k Ohm but I got a measurement of 5C instead 21C.


Replying to myself…I found the below info in a manual:

Thermistor R0 = 15kΩ ± 3%
B constant = 3480 ± 2%

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Can you share a link of such generic cheap thermistor?

Sorry for the delay, just saw the message today.

In case you are still interested, I found a customized thermistor in Aliexpress but I´m still waiting for it.

On the other hand, I ended up making a “fake thermistor” with a digital potentiometer (DS3502).

My Home Assistant server is monitoring several thermometers I have distributed around the house. I created a select input that allows me to select one of those thermometer and an automation sends via MQTT the temperature of such thermometer.

A ESP8266 board gets that temperature and configure the DS3502’s wiper to adjust the variable resistor to a value that is equivalent to a thermistor 15K and B=3480.

That allows me to fool the Ecodan with the temperature it’s seeing via CN20 connector.


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@Eduardo_G.D this last piece of info is awesome. I will try to fool Ecodan between my boiler and hot tub. Can you share the code for the ESP of how exactly it gets the temperature and sets the DS3502’s

Also can you please share the link to the DS3502. Thanks

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Please check the following link for DS3502

ESP gets the temperature by subscribing to a MQTT topic, how are you getting the temperature?