Recirculating Pump With Aquastat: What It Does and How It Works

Recirculating Pump With Aquastat: What It Does and How It Works

Recirculating pumps are becoming increasingly common in homes around the world. They’re an effective way to ensure that hot water is available on-demand immediately when you turn on the hot water side of your faucet. Aquastats are commonly included with recirculating pumps as a way of making sure that the on-demand water stays at the appropriate temperature. 

Just as a thermostat is used in your home to regulate the temperature of the air, an aquastat is used with your recirculating pump to regulate the temperature of your water. Without an aquastat, your recirculating pump won’t know how hot the water that it’s circulating is. It also won’t know when it should be heating water up or allowing it to cool. 

In this article, we’ll take a deeper dive into how aquastats and recirculating pumps work together. We’ll also look at everything you need to know about your aquastat and how to adjust it if necessary.  

What is the purpose of the pump aquastat?

The purpose of an aquastat is to control the water temperature of your boiler or recirculating pump. Traditionally, aquastats were paired with boilers to make sure the water controlling the temperature of your home doesn’t get too hot or cold. The concept of an aquastat with a recirculating pump is very similar. 

The aquastats’ job is to make sure that on-demand water present at your faucets stays at a consistent temperature. If your aquastat doesn’t kick in and tell your water heater that the water it’s producing is hot enough, the water generated by your recirculating pump will be dangerously scalding. If, however, your aquastat doesn’t tell your recirculating pump that more hot water is necessary, the pump is essentially useless and unable to do its job. 

How does an aquastat work?

An aquastat works in conjunction with your water heater and your recirculating pump. It tells your water heater if hot water is needed at a certain point. Your recirculating pump is responsible for taking hot water created by your water heater to predetermined points in your plumbing system. The result is on-demand hot water at select faucets and lavatories where the typical wait time for hot water is five seconds to a minute. 

All aquastats are equipped with two switches: the high limit switch and the low limit switch. The low-temperature limit or switch is designed to keep water from getting too cold within the system. On the other end of the spectrum, the high limit is meant to keep it from getting boiling hot and possibly damaging your plumbing system or burning someone when they turn the water on. 

While the job of an aquastat sounds somewhat complicated, the device itself is actually very simple in design. Aquastats consist of a limit switch, a temperature-sensing bulb, and a tube that connects the two. Both the tube and the bulb are filled with a liquid substance known as fill. 

The bulb end is inserted into the water and rests there to sense changes in water temperature. As the water heats up in temperature, the fill inside the bulb expands and stretches into the tube. Once it expands enough the fill will apply pressure to switch of the aquastat. This pressure is enough to turn the switch off and signal the water heater and recirculating pump to stop creating hot water. 

As the water cools down, the fill recedes in its size and eventually removes pressure from the aquastat switch. When this happens, the water heater and recirculating pump start creating and transferring hot water to the correct places, and the process repeats as long as the water heater and recirculating pump are turned on. 

Another important thing to note is that the aquastat tells the recirculating pump when it’s ok to send water down the system. Rather than constantly sending cool or lukewarm water through the recirculating pump water loop, aquastat doesn’t allow the valves in the recirculating pumps system to open up until the water is hot enough. 

Your water heater will continue to create hot water no matter what. This water won’t be allowed into the recirculating pump system, however, until the aquastat detects that it’s hot enough. The floodgates will then open and hot water will flow through your recirculating pump to the appointed areas in your plumbing system. 

How do you adjust an aquastat?

If you want to adjust your aquastat, the process is quite simple. Your aquastat should have a cover on the outside of it to protect the internal components. To adjust the temperature, you’ll have to remove the cover, which should slide up and off the top. Once removed, you’ll see the two switches typical of all aquastats, the high limit switch, and the low limit switch. 

The high limit switch makes it so that your water heater, boiler, or recirculating pump turns off before water exceeds the set temperature. The low limit keeps water from getting too cool within your system. To adjust either of these settings, simply turn the knob up or down. However, you should always make sure to keep around a 20-degree temperature difference between the high limit and low limit settings. 

Taco Aquastat

Taco is one of the leading brands in recirculating pump and aquastat technology. They have a number of great plumbing products, and the Taco aquastat is among them. Taco aquastats are compatible with most recirculating pumps and plumbing systems, but you should check with a qualified plumber before purchasing one for your system. 


Is an aquastat normally open or closed?

Whether or not your aquastat is normally open or closed depends on what your temperature setting is. The higher you have your aquastat set, the more likely it is that your aquastat will be open. However, aquastats at a lower temperature are easier to satisfy and will close sooner and more often. 

What should water heater temp be set at?

The safest water heater temperature setting is around 120 to 130 degrees Fahrenheit. However, it’s fairly common for residential water heaters to be set at 140 degrees. Anything less than 120 degrees presents the risk of bacteria infecting your water. 

Final Thoughts

As you can see, aquastats are an extremely important component of water heaters and recirculating pumps. It’s important, however, that you know how they work and how to adjust them when necessary. It’s also important that you realize how essential an aquastat is to your hot water system to ensure maximum efficiency and convenience. 

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