The Utica-Dunkirk 240008226 Return Water Temperature Sensor is a 12K Ohm NTC thermistor with a 3% tolerance and 22mm mounting bracket, designed to monitor return-water temperature in compatible Utica-Dunkirk heating boilers. The sensor changes electrical resistance as water temperature changes, allowing the boiler control system to accurately track water temperature and regulate heati... https://www.partshnc.com/utica-dunkirk-240008226-return-water-temperature-sensor-w-22mm-bracket-12k-ohm-ntc-3