Hot water recirculation pump sends warm water to cold line.

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Bob Heist

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We had a hot water recirculation loop installed during a remodel. Sometimes we get warm water from the cold line at kitchen sinks when no water has been used for awhile. When replacing the Grundfos pump, I looked at the installation. The pump is in the return of the loop and is "T"ed into the cold water inlet. The cold line has a swing check valve installed before the T. When the pump is running and no water being used, the cold water line is hot back to where it enters the wall. Not being a plumber, I am not surprised about the results. It seems to me that the pressure on both sides of the swing valve would be very close together and when the valve is in my hand the gate is slightly opened by gravity. Any suggestions? Would a spring valve work better? The swing valve is mounted horizontally. I wondered if installing it verticaly with the hot water on the top might allow gravity of the gate to seal better and restrict the leaching of hot water into the cold inlet. All of this plumbing is on top of the water heater, close to the ceiling. In a previous house our pump was mounted close to the drain outlet on the HWH and used that as a return to the tank. Would that be a good idea and according to code? BTW, there is also a swing check close to where the return loop enters the pump and the Grundfos has what looks like a plastic ball actuated check valve in the fitting. As I said, not being a plumber, I hope my language is understandable to one who plumbs.
 

Silversaver

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A picture worth thousand words.

How does recirculation going through cold inline? The pump automatic stop once it sense hot water in loop. Here is my setup just like your old house where pump install at drain.

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Silversaver

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I guess there were people install the recirculating pump at water inline. Some houses do not have the "runback pipe" so it uses the existing cold water line to return hot water to the water heater. There is the Comfort Series by Grundfos. I thought you have the new runback pipe installed.

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Jadnashua

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How far the hot water goes into your cold supply depends on a few things:
- where does the control sense the hot water?
- what temperature does the cross-over open up?
- how well does the check valve work?

Ideally, there would be a dedicated return line, but many retrofit situations rely on the cold water line for the return path, so that will get at least warm. With a dedicated return line, your cold supply would not be used, and should be either ambient or supply temp or somewhere in between.

My system senses the temperature immediately after the cross-over, and actually shuts the pump off verses just closing a cross-over valve. Some leave the pump running constantly and open/close the cr0ss-over as needed to ensure there's at least warm water at the hot supply. In my case, it's adjustable, and I have it set to be warm where it is sensing (the tub is closer to the supply, and is hot), so there is very little warm water pushed into the cold supply line (flushing the toilet generally clears it)
 
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