The Williams Furnace P322016 Millivolt Wall Thermostat is a replacement thermostat designed for compatible millivolt heating systems and Williams furnace models. It senses room temperature and controls the furnace by opening or closing the millivolt circuit to maintain the selected temperature. This replacement thermostat is suitable for replacing a worn or faulty original unit. Its d... https://www.hnkparts.com/p322016-williams-furnace-millivolt-wall-thermostat-only