My hot water circulating system was installed in 2006. It has a dedicated return line from all faucets. I've been having trouble lately with the hot water, it turns cold at the faucet when the pump is not on. I just replaced the back flow valve thinking that was causing my problem but I was wrong. Does anyone have any idea what might be the problem? The water goes cold after turning off the pump. It stays running cold until the pump is turned on or the circulating system is isolated from the rest of the plumbing. This occurs at all faucets. They are all single lever faucets. The water never gets hot again until I turn on the pump or isolate the circulating system. I do not know how it is hooked-up. What you say makes more sence. I think that the back flow valve may have been installed backwards. That would explain hot water turning cold when pump is off.

  • Does the hot water stay cold even if a faucet is left on for awhile, like 60 seconds?
    – wallyk
    Oct 25, 2013 at 15:33
  • yes, it may start out hot but becomes cold after a few seconds.
    – Steve
    Oct 25, 2013 at 16:53
  • Yes, but what happens after a minute or two? Does it stay cold or warm up again?
    – wallyk
    Oct 25, 2013 at 18:04
  • @steve, now that you've registered your account, see merging accounts so you have access to edit, comment, and accept answers on your own question.
    – BMitch
    Oct 26, 2013 at 2:11
  • Does this happen at one faucet or all? Is it a single lever style?
    – bcworkz
    Oct 26, 2013 at 16:13

1 Answer 1


Here's a diagram of a hot water recirculating system

enter image description here

As I understand it, the idea here is that the recirculating system runs hot water around the pipework to keep the temperature hot near the faucets/taps. This allows for instant hot water at faucets/taps far from the water heater.

Even when no taps are running the pump should be actively maintaining the circulation as needed. It needs to do this as any unlagged pipes will cool the water in them if no faucets/taps are drawing hot water.

When the water near the faucets/taps is sufficiently hot, the "Aquastat" will turn the pump off.

Your power feed to the recirculating system should be via a timer, or other device, that lets the pump run whenever the "Aquastat" feels necessary. This should be "on" during any times of the day when you are likely to use the faucets/taps.

Some ideas:

  • your timer isn't on or you are not allowing time for the pump to raise pipe temp.
  • your "aquastat" is faulty.
  • your "aquastat" is not near the faucet/tap you tried.
  • your configuration needs additional "aquastats" or the "aquastat" relocated.

You should be able to test this with a thermometer and a voltmeter if you can locate the "aquastat"

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