The following is a hot water recirculation line diagram, which shows how a recirculation line is a separate water pipe that runs off the hot-water line from the farthest plumbing fixture back to the water heater. A pump at the water heater moves hot water through the recirculation line. As illustrated here, we have a master point-of-distribution mixing valve that does not have 100% close-off on its inlet ports (most thermostatic mixing valves) can cause creep or droop if not properly piped. We also have a tank water heater or tankless water heater connected to bathrooms, laundry, and kitchen. We can use EdrawMax to create such great-looking line diagrams.