I have a Grundfos hot water circulator. After turning off the main to the house and the hot water circulator the other day to change out a valve for our dishwasher, the hot water circulator hasn't been working properly (making horrible noises, not sending out water properly).

From what I've read it seems that the hot water circulator has seized. We've unplugged and replugged, and tried to turn the bolt on it, but it won't move. Again, from what I've read, this indicates we probably need to replace with a new unit.

My belief was that we would still have hot water (as we would if we didn't have a circulator), however we are not getting sustained hot water in our showers both upstairs and downstairs (after about 5 minutes the water is warm, but then turns cold). What would cause that? I am hoping to figure out how to have hot water access until we can get the unit replaced.

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2 Answers 2


Pressure from the cold side is higher than from the hot side, so cold water is backfeeding through the circulator and on to the hot side to the faucets in use. Close the shutoffs you have for the circulator and the problem should go away.

  • Do I need to close both or should one cover it? The one UNDER the pump is not turning at all. Mar 3, 2016 at 18:52
  • I assume the pump in question is the red one in the picture? One valve of the two in series should be all you need to close to stop the backflow.
    – Jeff Meden
    Mar 3, 2016 at 19:16
  • Perfect! It worked like a champ. Thanks so much! Mar 3, 2016 at 20:23
  • When you replace the pump you should use a cord grip on the cord. The wire entering the pump can rub and short circuit or worse cause a fire.
    – ArchonOSX
    Mar 3, 2016 at 21:31
  • Also, there is what appears to be a backflow preventer that is probably not working (hence this problem), it's that little globe looking fitting below the lower shutoff. You might look into fixing that while you are at it. Good luck!
    – Jeff Meden
    Mar 3, 2016 at 22:02

Everything is very aged. Down the road you will need a new system. Get some quotes from smaller established companies. If you want it to be right, which would include gas work (get rid of the flex line). In my area flex gas lines need to be grounded because of lightning.

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