The Taco 5201-4 Heat-Gard Operator is a thermostatic control component designed for hydronic heating systems to regulate room temperature. It works by sensing changes in surrounding air temperature and adjusting the connected valve to control the flow of hot water or steam through the heating equipment. Compatible with Taco Heat-Gard thermostatic valves used in baseboard heaters, radi... https://www.partshnc.com/5201-4-taco-heat-gard-operator