The shower and hot water heater are far apart. So every time we want to use the shower at least 3 gallons of water go down. To save water I put a hot water circulation pump in with an eye towards it being energy efficient. The normal way they are used is they get installed on the hot water heater, a timer runs the pump potentially several hours a day. Well I don't like that. I want to keep hours off the pump so it lasts longer and I don't want to keep circulating hot water when it's not going to get used. So I installed the circulation pump near the bath room in an adjacent laundry room. Ran it on a timer and temperature switch. The timer runs the pump until the temp switch shuts it off, then the timer times out before the water in the line cools off. First problem, when the hot water is on it sucks cold water back through the pump and cools off the water. Not good. Fixed that by adding a flapper check valve. Second problem, when I open up the garden hose spigot it sucks hot water through the hot water line through the pump and check valve. Thats not very energy efficient. I ordered a big 120v 3/4'' solenoid valve. That should eliminate the unwanted hot and cold water mixing problem. Should save well over a thousand gallons of water per year and send semi warmed water back to the hot water heater instead of running it open loop and putting 3 gallons of cool ground water in the hot water heater.