Yes, Themo is compatible with most existing NTC (negative temperature coefficient) temperature sensors. Natively Themo supports the following NTC sensors:

NTC 6,8 kOhm 

NTC 10 kOhm

NTC 12 kOhm 

NTC 15 kOhm 

NTC 33 kOhm

NTC 47 kOhm

When using existing temperature sensor, make sure that the correct sensor is configured when setting up Themo in web interface. Which temperature sensor do I choose?