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.

This is a brilliant idea, and for that it earns a star. As for execution, not so much. I have a 1/2" copper pipe in my dedicated recirculation system that heats up to 122.3F; clearly above the stated "105F +/- 5F" window for device cut-out. It does not cut out. Consequently, my pump would continuously run until the timer shut it off. This is not acceptable, as you can imagine.I have returned this one as defective, and I've ordered the 3/4" device with the same stated temp range of 105F +/- 5F, thinking the additional surface area on a nearby 3/4" copper pipe may help. I also ordered thermal transmission grease used on CPU heatsinks, and I intend to clean the pipe with steel wool before applying the grease and the unit. We will see. Those comments will appear under the 3/4" unit after I test.If that doesn't work, I'll probably try a Honeywell adjustable aquastat and somehow modify it to be in direct contact with the pipe.

This is a great companion to go with your timer on a water circulating pump. Water temperature hits the setpoint (not adjustable, sadly) and the pump shuts off, even if the timer hadn't reached it's shut off point yet. I'd buy this again.

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

I tried the high temp switch and had to return it for this low temp version. I would say it come on about once an hour for about 2 minutes per use. Works perfectly!