The cold line is "upfeeding" hot. Both of the pipes running out of the hot water heaters(dual system) are hot. When we run the hot, it gets cold again. The cold feed pipe is hot until it reaches the T where it first splits from the main feed. Have had 2 plumbing companies out and nothing. All singke handle faucets and showers are off.

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    Hello, and welcome to Home Improvement. This is a bit confusing; a bit more explanation, and perhaps a diagram, would really help us help you. – Daniel Griscom Dec 6 '18 at 13:28
  • Are you saying that the cold water feed pipe to a hot water heater feels warm to the touch? And it starts to get cold when you turn on one of the hot water taps in the house? – mike65535 Dec 6 '18 at 13:50
  • Yes it is very confusing. We have two hot water heaters. They are cross connected. The cold feed gets very hot and is hot all the way to the first T joint from the main. The hot side somtimes goes cold but most of the time we have two hot pipes for some reason. – Mike Dec 6 '18 at 13:51
  • Mike65535 yes that is the case – Mike Dec 6 '18 at 13:52
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    Are you sure it's backfeeding and not just conducting heat? – isherwood Dec 6 '18 at 14:09

It is possible that the 1 water heater is pressurizing the line and using the other water heater like an expansion tank. I have seen homes that did not have check valves or pressure regulators have this problem when the water heater heated it pushed the excess pressure back so the inlet would get warm. I believe there was also a post where this cost the home owner because the water meter doesent count back flow but with the water heater heating and cooling and no other water usage the post said it increased there water bill until a regulator or check valve was installed.

  • We have a check valve installed but it seems to not be working. But a regulator you say? First time we've heard that. – Mike Dec 6 '18 at 15:25
  • By using a regulator to drop the pressure feeding the tank when it pressurizes it won't be enough to back feed the water meter. I have not had that problem but one poster said it made a huge difference in there water bill. – Ed Beal Dec 6 '18 at 15:32
  • Excellent suggestion, something I'd never have thought of. – Gary Bak Dec 6 '18 at 23:18

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