The Lochinvar & A.O. Smith 100110950 Thermostat Lower Probe is a replacement temperature-sensing component designed for compatible commercial gas water heaters. It works by monitoring the water temperature in the lower section of the tank and sending temperature readings to the thermostat control system, helping regulate heating cycles. Commonly used in Lochinvar and A.O. Smith commer... https://www.partshnc.com/100110950-lochinvar-ao-smith-thermostat-lower-probe