My water heater has a shutoff valve at the cold inlet. The shutoff valve was closed and cold water line was disconnected from the water heater. I wanted to restore water to the house while I work on the water heater. When I opened the main water shutoff valve, cold water entered the water heater through the hot outlet and overflowed out of the cold inlet.

Is this normal? How did cold water enter the hot line? Also what is the device with the knob at the top in the pic below?

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Thanks for help.

3 Answers 3


Single handle faucets can allow water to flow from the hot side to the cold if turned on at all. Not sure if some of them will allow the flow when turned full off. Fix would be to turn off the hot water shutoff valve under your sinks. If the flow is coming thru a bathtub or shower valve, that would be more difficult. Might be easiest to simply remove the flex pipe on the hot side where it connects to the galvanized pipe and cap it off for the duration of your project. You'll probably have to replace the flex pipe as the gaskets tend not to be very reusable.

  • I have had the same thing happen. Had to run to town to get some parts and the home owner used the water causing a small flood. She did not understand why I said not to use the hot but cold was ok.
    – Ed Beal
    Commented Mar 22, 2021 at 14:01
  • Any idea what that device with the knob at the top is?
    – davidvu90
    Commented Mar 23, 2021 at 2:24

The valve may have failed internally ; the handle still turns but does not close the valve. I had one fail in that manner last month.

  • I disconnected the cold water line from the WH cold inlet. Water was not coming out of the disconnected cold water line.
    – davidvu90
    Commented Mar 22, 2021 at 16:17

Get a 3/4 x 6 brass nipple and then after shutting water off at water heater disconnect the copper flexes at hot and cold side at the water heater and install and tighten the brass nipple between the flexes to make a loop(bypass)

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