Grundfos 595656 Aquastat Control, Black

An Aqua-stat turns a hot water heater's recirculating pump ON when it's needed & then OFF a few minutes later when the Aqua-stat senses that the pipe that it's clipped onto has gotten warm enough. I've had them on my houses over the years.For best results, it needs to be clipped onto to copper tube that comes out of the wall to bring water down to the recirculation pump with the Aqua-stat hanging down so that its temp sensor is touching the tube where there's always water inside and never air bubbles.That temperature range that it operates within are stated in the part's description. They're easy to install yourself as long as you're comfortable doing a really little bit of wiring.It can be easily used with any brand of recirculation pump, and you can ignore the installation instructions that come in the kit and the 2 extra little pieces that are just for mounting it to the Grundfos (I think) (see those in photo).All you do is slit the existing power cord (UNPLUG IT FIRST!) in-between the 2 wires out near the recirculation pump and then cut & strip just 1 side of the recirculation pump's power cord about 3/8" on each wire. Leave the other side alone.Then, use the 2 tiny wire nuts that came in the kit to connect the Aqua-stat into that wire. It can be wired either way but I was told to connect the white Aqua-stat lead onto the power cord and the black Aqua-stat lead onto the recirculating pump.There's only 2 sizes of these Aqua-stat kits and this smaller one is for most modern homes. The 1/2" in the description is the ID of the copper tubing that it clamps onto, so don't let that confuse you. The OD is about 5/8".Mine must have an internal electric or mechanical issue that's keeping it from working properly so I'm returning it but I'll get another one. 👍

Although maybe this is obvious, it was not to me, so I thought I would explain to make it clearer.For this exercise let's assume your hot water heater is set to 140 degrees.If your hot water recirculation line has a Grundfos pump and NO thermostat (timer or no timer), your pump will run 100% of the time it is set to be on. It will be circulating 140 degree water through your recirculation line. When your hot water is turned on it will be instantly 140 degrees.The Benefit: Instant 140 degree hot water.The Negative: Wear and tear on your pump & pipes. Danger of users scorching themselves with instant 140 degree water.If your hot water recirculation line has a Grundfos pump and this thermostat (timer or no timer), your pump will run a fraction of the time of the time it is set to be on (only when the water temp is between 105 -110 degrees) . It will be circulating 105 - 110 degree water through your recirculation line. When your hot water is turned on it will be somewhere between 105 -110 and will quickly heat up to 140.The Benefit: This will SAVE wear and tear on your pump & pipes. Users of hot water are less like likely to get scorched by water that is too hot. ENERGY (electricity to run the pump and electricity/gas to heat the water).The Negative: Only that your water will not be instantly 140 degrees. This thermostat is set PERMANENTLY at 105 - 110 degrees and cannot be changed.There is another version of this thermostat that is set PERMANENTLY at 85 - 105 degrees. I tried this version first and although it does save more energy and the pump almost never ran, the water was NOT hot enough for me.The 105 - 110 model is the perfect temperature for me.

Worked great up until 1 month ago & I noticed an unusually high power bill. After troubleshooting I found it had failed in the closed position making my pump run 24/7. At the price point of these they should last much longer than this one did. It didn't quite last a year.

Hard wire in series with your neutral wire on the plug for the recirculating pump. Will take full AC power. Kills the power to the pump when it hits the listed temp then kicks back on at the lower temp. Works great.

Fits psi just fine. The temperature is set and unadjustable. Customers want hotter water than 85 degrees

Simple to install with a basic hot water recirculating pump. Works great and it's a lot cheaper(and more convenient) than a pump with an integrated timer.

I installed this with a dedicated return line and recirculation pump to keep water warm at the farthest points of the house.The water heater keeps water at 120F (verified with thermometer). The Aquastat I purchased is the 105-115F model. It never shut off the pump.I raised the water heater to 125F (verified with thermometer at faucet directly in hot water flow.). Still didn't turn off.I raised the water heater to 130F (verified). This time it started to cycle the pump. However the cycle time was 5 minutes on, five minutes off.I covered the section of pipe (1/2 copper tube) and aquastat with insulation. Cycle time changed to 5 minutes on, 10 minutes off.The aquastat doesn't do an adequate job of controlling by temperature. 130F is too warm to enable use of a 115F control. (burns are possible).Seller was fast and the price is fair. I just don't think it's a good idea and/or design.My idea was wrong: the pump really needs to run constantly or you have widely varying water temperature at faucets/showers. Turn it on and it may be at the low-end temp of the cycle to have it creep up on you. If at 130F at the tank this could result in scalds.Set the tank where it should be, and run the pump using a smart outlet (wifi) you control on a schedule or command via smart speaker. You can even set it to run 5 on/10 off but then have varying water temps. I think it's better just to run it and insulate pipes if you have access.If you can't insulate the pipes you really need to consider whether you want to do this at the expense of wasting heat into the walls summer and winter.