My hot water heater started leaking today, so I turned off water to my house at the curb. After the tank was drained, I disconnected the cold line and turned off the valve right above the hot water heater.

When I turned water back on at the curb, water started coming in to the tank from the hot line, eventually reaching ~0.5gal/min coming out the drain.

There were no faucets on in the house. What can cause this behavior? My hypothesis is that it could be the shower mixing valve but I'd like to confirm it's just that and not something more... sinister. (lots of lousy DIY work in this house from the previous owners).

  • 1
    could be the shower mixer (or any other mixer) but only if you turn it on. do you have a temperature limiting valve on the hot side of the heater?
    – Jasen
    Commented Jan 19, 2020 at 5:26
  • Hmm.. all faucets, showers included, were off. There is no valve between the hot side of the heater and the wall.
    – Philip
    Commented Jan 19, 2020 at 5:28
  • 1
    you may have to fox-hunt the source of the flow by ear.
    – Jasen
    Commented Jan 19, 2020 at 5:32

1 Answer 1


Mixing valves could be the problem and depending on the year built or later faucet replacements the kitchen faucet and bathroom faucets are also possible causes. By turning the shutoff valves the guilty valv should be able to be identified.

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