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Thread: Hot water from cold faucets

  1. #1

    Default Hot water from cold faucets

    I moved to this two story house 5 years ago. Ever since, I get hot water from the cold faucets for few minutes until the water gets cold again.

    I removed the plug from the pump but the problem did not go away

    I closed the hot water return valve to stop the circulation but the problem did not go away.

    My installation uses a Grundfos UP 15-42 SF pump and it has a hot water return pipe. It seems to be professionally done at the time the house was built in 1991.

    Please help.

  2. #2
    Plumber krow's Avatar
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    It is possible that you may have a cross connection in a faucet somewhere. I don't know why that would be in a residential application . It usually happens on commercial installations where they choose to leave the faucets in the on position and the check valves fail.

  3. #3
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    If you have a hot water recirc pump it could be pumping so fast that you're actually heating the water in your cold water pipes. When you draw fresh cold water it purges that hot water and it gets replaced by cool fresh water coming in to the house.

    Jason

  4. #4

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    I tried with the pump off and even with hot water return valve off and got the same problem.

  5. #5

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    krow,

    I am sure hot water is going in the cold water supply but I still cannot figure out how would that happen.

    What is a cross connection? Do you mean Hot water connected to the cold side and cold water on the hot side of a faucet? Why would that cause a problem in the whole line as opposed to only on that faucet I would get cold from hot and hot from cold? I am asking and being specific because I do have one such connection in my outdoor faucet, but before I make the change, I want to understand how would that cause a problem.

    Thanks.

  6. #6
    Plumber krow's Avatar
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    Quote Originally Posted by jackstephan2000 View Post
    krow,

    I am sure hot water is going in the cold water supply but I still cannot figure out how would that happen.

    What is a cross connection? Do you mean Hot water connected to the cold side and cold water on the hot side of a faucet? Why would that cause a problem in the whole line as opposed to only on that faucet I would get cold from hot and hot from cold? I am asking and being specific because I do have one such connection in my outdoor faucet, but before I make the change, I want to understand how would that cause a problem.

    Thanks.
    A cross connection is when a faucet allows the hot water to circulate into the cold side just by gravity. As I said earlier, it usually happens when faucet check valves fail. Your indicating that you may have a connection of hot an cold together and if you don't have check valves or shut off the hot side for your outdoor faucet, that could cause the circulating by gravity.

    Depending on the proximity from your faucet to the possible cross conection or in a direction of flow or even from your hot water source (stranger things have happened)

  7. #7
    Plumber Cass's Avatar
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    Questions.

    Does the water get hot or just warm?

    Does it last a few min. or less than a min.? Have you timed it?

  8. #8
    Plumber jimbo's Avatar
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    The pump is the issue. With the pump off and the return isolated, does the problem persist even after you have run enough cold water to clear out the line....does the hot return the next time you run the cold tap?

  9. #9

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    Quote Originally Posted by Cass View Post
    Questions.

    Does the water get hot or just warm?

    Does it last a few min. or less than a min.? Have you timed it?
    The water runs hot not just warm. It lasts few minutes then I start getting cold. I shut down, wait five minutes, then the same thing happens. I never timed because there are so many variants that can affect the duration.

  10. #10

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    Quote Originally Posted by jimbo View Post
    The pump is the issue. With the pump off and the return isolated, does the problem persist even after you have run enough cold water to clear out the line....does the hot return the next time you run the cold tap?
    I doubt it's the pump, but to answer your questions, yes even after I empty the pipes, I shutdown the faucet for five minutes and open it back again and I get the same behavior.

  11. #11

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    Quote Originally Posted by krow View Post
    A cross connection is when a faucet allows the hot water to circulate into the cold side just by gravity. As I said earlier, it usually happens when faucet check valves fail. Your indicating that you may have a connection of hot an cold together and if you don't have check valves or shut off the hot side for your outdoor faucet, that could cause the circulating by gravity.

    Depending on the proximity from your faucet to the possible cross conection or in a direction of flow or even from your hot water source (stranger things have happened)
    I think you are right about the cross connection. What I am saying about the outside sink is that the hot water pipe is connected to the cold faucet and vice versa, I doubt that's the cause. Now some history. Before I moved to the house I did some repairs and installed a shower with a thermostatic valve, I think that's where the problem is because my wife says the problem is worse in her sink which is the closest to that shower. Another thing I noticed is when the pump is on, I get cold water for less than a minute followed by hot water for few minutes then cold. With the pump off, hot water starts immediately for few minutes then cold. This behavior I noticed in my sink near that shower. I think when the pump is on, it moves the hot water from the problem area continuosly and that is why I get cold then hot then cold. I think I should turn the pump off and see at which faucet I would get the worst behavior and that would be the nearest point to the problem.
    Another reason I think it's the thermostatic valve is that recently the situation is worse and the shower does not get as hot as before even on the highest setting. Am I on the right track?

  12. #12
    Master Plumber Redwood's Avatar
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    Can you feel supply pipes to individual fixtures? I.E. pipes in the basement.
    If so look for the hot cold line.

  13. #13
    Plumber krow's Avatar
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    Quote Originally Posted by jackstephan2000 View Post
    Am I on the right track?
    You are on the right track . I suspect that valve may have a cross over. It doesn't happen often, but it does happen . Being a thermostatic valve, you may have stops or valves built into the shower valve, see if you can isolate that valve off and see if it makes any difference.

    At this point , it will be trial and error to track down the cause of your problem

  14. #14

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    Quote Originally Posted by krow View Post
    You are on the right track . I suspect that valve may have a cross over. It doesn't happen often, but it does happen . Being a thermostatic valve, you may have stops or valves built into the shower valve, see if you can isolate that valve off and see if it makes any difference.

    At this point , it will be trial and error to track down the cause of your problem
    We got it!!

    Why it's happening is strange but this is the story and the short term solution:

    It turns out that the problem does not happen if we leave the thermostatic shower valve in the coldest postion, which we never do. We always kept the dial on the comfort showering temperature which we never got because of this problem.

    So now, if I keep it on cold when not in use, the cold water is normal in the whole house. We just need to turn the dial to hottest just before we take a shower and turn it to coldest right after we finish a shower.

    When I remove the decorative cover, I can see the valve. It has one little control screw on each side (hot and cold). They are both set to the maximum (out) position. Do you know what those control screws do and if they can be adjusted to fix this problem?

  15. #15
    Plumber krow's Avatar
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    Quote Originally Posted by jackstephan2000 View Post
    Do you know what those control screws do and if they can be adjusted to fix this problem?
    They are stops or shut off valves for your unit. They are for shutting off your unit to make repairs on the faucet.

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