Abstract: In a hot and cold water distribution system wherein the hot water is delivered from a water heater to a distant hot water tap adjacent to a cold water tap, a hot water recirculation pump assembly purges the hot water line of any cooled-down water in order to assure instant hot water delivery when the hot water tap is opened. The volume of water drawn from the hot water line is, in a first embodiment of the invention, cooled down through a radiator before being recirculated through the cold water line faucet. In a second embodiment, the volume of cooled down water is flushed back through the hot water line by admission of an equal volume of cold water in that line. That volume of cold water is immediately pumped back into the cold water line, and automatically replaced by hot water drawn from the water heater. Each embodiments prevent any drawing of lukewarm water from the cold water tap. The pump assembly includes a pressure-sensitive check-valve in the pressure region of each pump.