Review on Highly Efficient 110V NPT3/4'' Domestic Water Circulation Pump With 3-Speeds For Hot Water Recirculation And Solar Heater/Faucet Applications (RS15/6G) by Jay Chenier

I purchased this pump for an under-sink on-demand pump to get hot water without wasting a lot down the drain. It replaces a cheaper pump I had that started leaking. I have it running from the hot water supply to the cold below my bathroom sink. The good - the pump is extremely quiet. Almost can't hear it. The disappointing: 1) It doesn't prevent flow through when not in operation. So without a check valve, the hot and cold water will mix through the pump, warming the cold water and cooling the hot water. I installed a spring loaded check valve, that closes on the hot water side, thinking that it would seal the hot water when I am running cold from the tap, the spring holding it shut against siphoning. That works to a point. When I have the hot water line fully open (at the under-sink shutoff), there is apparently enough hot pressure that the cold line siphons some in thru the check valve when I run the cold at the tap, making it warm. If I partially close the hot shutoff valve, that allows the cold tap to run true and not siphon in any hot. However, that reduces the hot flow at the tap, and restricts the flow the pump is pulling when on, lengthening the time it takes to get the hot water there. So not a perfect solution for my use.