So what this does is move the hot water through the pipes constantly, not just when you need it? Seems like an energy suck. Is it?

If you run this all the time you will likely increase your water heating costs significantly as you are turning your pipes into a big radiant heater. You can use the built in timer to only have it come on at set periods, but this will only work if you have a very fixed schedule. I attacked this another way. I plugged the unit into a TP-Link HS110 Smart plug that is Alexa controlled. I can just say turn on hot water pump or turn off hot water pump when I want to control it. But that was not good enough for me. I found that if this pump ran for four minutes it would give me hot water at the distant shower that I wanted, so I did the following. I wrote a routine to turn on the pump, wait four minutes and then turn it off. While I can run this by voice, I bought the new Amazon Alexa Button, they are about $14 for a two pack. The button is battery operated and communicates to another Alexa device. Just before I take a shower I push the button and within four minutes the water will be hot without having to run water.

If the pump is on, and the water is hot, the sensor valve closes, right? Isn't the pump trying to push water against a totally closed line?

The pump just stirs water in the pump housing. It's not a positive displacement pump, so it has no problem doing that. But most of the time the control valve allows a trickle of hot water to flow, just enough to keep the faucet temperature at a constant 100°.

can i used without the sensor valve

The control valve keeps the water temperature at the faucet at 100° by slowing the flow to a trickle. If you don't use the control valve, be prepared for the hot water to circulate at full speed and the temperature at the faucet to go up to whatever your water heater is set for.

Does this shut down the flow completely once temperature is reached or will it continue to trickle water into the cold water line?

The valve allows a slow flow of water back through the cold water line, enough to maintain the temperature at the faucet at about 100°F. If you let the hot water run, the temperature at the faucet goes over 100°F, and the valve shuts off the back flow through the cold water line. After the faucet is shut off, the water in the valve will cool to below 100°F, and the valve will crack open and allow some flow to keep the water warm. The valve does not bang open and shut. It opens more or less, as needed to keep the water warm at the faucet. It doesn't depend on the temperature set at the water heater, except that if the water is very hot, obviously it takes less to keep the water warm at the faucet. The valve accomplishes this automatically.

Brand	Watts Premier
Colour	Blue
Material	Aluminium
Style	Pump
Product Dimensions	15.7L x 15.2W x 12.7H Centimeters
Power Source	Corded Plug
Item Weight	6.4 Pounds
Maximum Flow Rate	6 Liters Per Minute
Voltage	120 Volts
Global Trade Identification Number	00098268254761
Manufacturer	Watts
UPC	737946470047 733353301905 798813036773 752913142826 735090278151 098268433470 098268253764
Item model number	Instant
ASIN	B000E78XHG

Watts Hot Water Recirculation System with Programmable Timer for Tank Water Heaters, Instant Hot Water, 120V Pump, 10 ft Cord, 2 Adapters, Sensor Valve, Mounting Screws, 2 Supply Lines (0955800)

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