Hot Water Circulator:

Hollis Sewer and Drain Cleaning Instant Hot Water Re-circulating System is a pump and valve combination that delivers hot water in an instant to any faucet or bath in your home.  It uses the pump at the water heater along with the patented under-sink sensor valve installed furthest away from the water heater.
This combination creates a pressure differential that allows the cold and cool water in the hot water supply line to "bypass" (at a low volume) into the cold water supply line through the thermostatically controlled sensor valve, keeping the water in the hot water supply line at a "no-wait" temperature throughout the home.  The timer on the pump makes it more efficient during downtime.
A re-circulating pump brings instant hot water to any room in the house. There are two types of re-circulating systems, closed systems and open ones. Recirculation decreases the amount of cold water that enters the system, and that results in much less condensation and less thermal stress on the tank.