Hydrolevel Hydrostat 3250-Plus Aquastat Universal replacement for common aquastat models, Provides cold start and thankless coil operation,easy to set, dial type limit settings,Industry standard wiring designations Easy to Install no outdoor sensor required, Works with virtually any boiler Protects boilers from damaging low water conditions Lowers the boiler temperature to save fuel without sacrificing comfort Easy to set just dial in the number of heating zones