Abstract: A thermal check valve for use in a gravity flow hot water recirculating system. The hot water system has a hot water heating tank, a water faucet, manifold piping from the hot water heating tank to the faucet, return piping from the faucet to the hot water heating tank, and a thermal check valve interposed in the return piping and adjacent a return inlet into the tank. The check valve has a valve body, an inlet chamber formed within the valve body, an inlet port in communication with the inlet chamber, an outlet chamber formed within the valve body, and an outlet port in communication with the outlet chamber, the outlet port being below the inlet port.