Alpha Thermistors
The thermistor works by decreasing current resistance in a manner that is inversely proportional to the temperature of the thermistor. The printed circuit board sends a current to the thermistor and can tell whether a decrease or increase in temperature is needed by the relative resistance provided by the thermistor.
Alpha 1.028395 DHW Negative Temperature Coefficient Probe - Intec/Eco
Part No: 1258727 / MPN: 1.028395