Viessmann Thermistors
The thermistor decreases the circuit resistance as the temperature increases. The electronic control board sends a current to the thermistor and can tell whether an increase or decrease in heat is needed by the resistance provided by the thermistor.
Viessmann 7819967 Boiler Sensor - 3 Wb1/Wb2 - Combi/System/System ERP
Part No: 2320068 / MPN: 7819967