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Grundfos dhw recirc problem

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I've just installed a Grundfos dhw recirc system and I'm not getting flow. This is between the indirect in the basement and the upstairs bathroom sink. I've purged air out of the lines and I'm getting both hot and cold water flow at the upstairs sink but there does not seem to be flow through the Grundfos bypass connection that is installed under the sink. I've confirmed that the circulator is running and and that the bypass valve is installed correctly. Anyone have any experience with this and / or suggestions? Originally thought that maybe we were getting bypass somewhere else, but no return of hot water via the cold water line even after 30 minutes of the pump running.

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  • Larry Weingarten
    Larry Weingarten Member Posts: 3,335
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    Hello, To start, is the pump overheating? I'm wondering if there is actually flow through the pump. If it's not overheating, than there must be flow and we need to figure out where that flow is.

    Yours, Larry
  • EtnaChris
    EtnaChris Member Posts: 4
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    thanks, Larry, no, the pump doesn't seem to be getting hot. I think the pump is deadheading or we'd see hot water coming back to the indirect via the cold water line, right?
  • Alan (California Radiant) Forbes
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    As long as the pump is working, water should flow to and from the fixture until the thermostatic bypass at the fixture senses 100°F water when the valve inside the bypass closes. The pump will continue to run, but since the bypass valve is closed, there won't be any water movement until the temperature drops and the bypass valve opens.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    EtnaChris
  • Ironman
    Ironman Member Posts: 7,379
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    EtnaChris said:

    thanks, Larry, no, the pump doesn't seem to be getting hot. I think the pump is deadheading or we'd see hot water coming back to the indirect via the cold water line, right?

    Not correct. The manifold valve closes as soon as hot water reaches it. There's only a small amount of hot water the goes into the cold side.

    How about posting some pics of the manifold and pump?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Zman
  • Zman
    Zman Member Posts: 7,573
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    Is there hot water at the faucet when you turn it on?
    As mentioned above, the water should never return to the indirect hot.
    I had one of these installed in my house and removed it. It did a great job of giving me immediate hot water to the taps. I got tired of having to wait to get a cold drink of water. The cold side was always luke warm.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EtnaChris
    EtnaChris Member Posts: 4
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    aha! That is the problem (my understanding of how the bypass valve works. I thought there was always flow through the valve, I didn't realize that it closed once it sees 100 degree water. So, when I turned on the hot water tap to purge air out of the line and to confirm that I was getting sufficient hot water flow, I caused the valve to close and that's why i don't see any flow. Got it. Thanks very much, I knew this crew would get me straightened out in a hurry!
  • EtnaChris
    EtnaChris Member Posts: 4
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    Oh, geez, now I've got a different problem. I actually WANT flow back to the indirect. This set up is being controlled by a thermostat not a timer. The idea is to cause water to flow through the hot and cold water lines leading to this upstairs bathroom because the lines go up through an outside corner chase that gets cold enough to freeze the pipes a few times a winter. It is a brick building and the inside side of the chase is lath and plaster so getting in there to insulate it properly is a major undertaking and not in the cards for now. My thought was a thermostat set at 35F controlling the pump would keep the water moving and even dump a little heat into the chase. With this thermostatic valve that won't happen as I understand it. Could I just drill out the thermostatic element, or would I then pull hot water through when the cold tap is turned on and vice versa? Any other solutions that anyone is aware of? As I understand it earlier versions of this bypass valve DID cause flow back to the indirect, is that correct? If so, are they still available? Thanks in advance for any insights.
  • Ironman
    Ironman Member Posts: 7,379
    edited October 2020
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    The only way you could get flow back to the indirect is if you had 3 pipes (Hot, Cold & recirculate).

    No, don't try and modify the valve; that will only cause a major cross connection problem.

    Just turn the pump timer switch to "ON" when you're having extremely cold weather and there should be sufficient heat and circulation (not guaranteed).
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    EtnaChris
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,335
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    Hello @EtnaChris , I imagine you could plumb a bypass with a valve in it around the Grundfos bypass. Then, when it gets cold, open it and turn on the pump as @Ironman suggested. You may have no cold water, but no frozen pipes either. :#

    Yours, Larry
    EtnaChris
  • Zman
    Zman Member Posts: 7,573
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    I would think it prevent freezing as is. Those valves need to let a trickle go through in order to get an accurate reading of water temp. You only need a trickle to prevent freezing.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EtnaChris
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,050
    edited October 2020
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    I've only installed one of these Grundfos recirc. systems and my customer was not happy with it. Only 100°F and you still have to wait for the high temperature water.

    I'd check with Grundfos to see what kind of flow there is when the valve is closed. Depending on the length of the pipe run and the outdoor temperature, it could still freeze.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    EtnaChris