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Thread: warm water from cold water line

  1. #1

    Default warm water from cold water line

    The cold water line downstream from the water heater is siphoning water from the water heater causing the cold water to be warm when it come out of the faucet. What do I do?

  2. #2
    Master Plumber Redwood's Avatar
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    You look for and eliminate the cross over!
    Usually a faucet that the hot and cold can be turned on and the outlet plugged, a recirculation system problem, or, a defective single handle faucet valve.

  3. #3

    Default warm water from cold water line

    There is a "T" that feeds the water heater and then keeps going to a few outlets. If I turn off the valve to the heater I get cold water downstream. Is there such a thing as a one way valve going to the water heater to prevent this siphon?

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by truckeebirdie View Post
    There is a "T" that feeds the water heater and then keeps going to a few outlets. If I turn off the valve to the heater I get cold water downstream. Is there such a thing as a one way valve going to the water heater to prevent this siphon?
    It's not siphoning, I guarantee it!
    What you decribe is a normal cold distribution system...
    There is another problem!

  5. #5

    Default warm water from cold water line

    I'm very confused. When I turn off the hot water supply valves at the downstream faucets I still have warm water. It's not just one downstream outlet that has this problem, it's everyone.

  6. #6

    Default warm water from cold water line

    Also if I turn on a hot water faucet upstream to the heater I get cold water at the downstream faucets.

  7. #7
    Master Plumber Redwood's Avatar
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    What have you got for single handle mixing valves on tubs, showers, faucets?
    Have you got any Mixet or Moen?

  8. #8

    Default warm water from cold water line

    One is a Moen, one is a Danze and two of them don't have mixing valves (two handle systems). They ALL have the same problem. And, as I stated before if I turn on a hot water faucet upstream to the heater I get cold water at the downstream faucets/outlets. I don't see how the problem isn't from siphoning from the water heater.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    One or more of the faucets has a cross-over and is letting hot water flow as well as the cold. Assuming the faucets have shutoffs (like at the vanity or kitchen sinks), shut them off one-by-one and see if the problem goes away. If it does, that will be the one you need to repair. You probably don't have shutoffs for the tub/shower. So, if shutting off all the others doesn't resolve it, then it's probably the shower.

    It's possible it could be the washing machine, too. Shut the supplies off from it in the test.

    If you shut off the supply to the WH, and you get cold, the only place it could be coming from when opening a hot faucet somewhere is if there's a crossover. How hot or cold things are when there's a crossover will depend on the relative restrictions in the two supplies.

    While not common, a tempering valve could also produce this...there might be one on the outlet of the WH or maybe to a toilet (if it was condensing, they may have mixed hot to prevent that with a tempering valve).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default hot water

    You would see it if you knew how a siphon worked. If your Moen faucet is mixing hot water into the cold line, it WILL STOP doing it when you turn off the valve to the water heater. You may be confusing your causes and effects.

  11. #11
    DIY Junior Member McHub532's Avatar
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    I recently moved to Arizona and had a similar problem.
    1. When I turned up the water heater high enough so that my dish washer would become effective.. we started to get very hot water even on the cold faucets and in the showers.
    2. I found these "T"s under each sink. Hot water into the left and up on the left, Cold water on the right and up on the right.. then lines went up to the faucets.
    3. Taking them apart and looking at them.. it ends up if the water got "too hot" it would release pressure and hot water into the cold water side of the T.
    4. This was not only causing the cold water lines in the faucets to become HOT, but it was backfeeding into the entire cold water line so even the showers were crazy hot.
    5. I removed all the "T"s and now we have no problems. We have cold on the cold side, and hot on the hot side.

    I have recently moved to Arizona so I don't know if this is a State Code issue or what.. but it was utterly stupid. A built in cross connection at every sink; rather than a pressure relief at the water heater.
    It has a relief at the water heater also.
    Guys at work say that most water lines here in Arizona go up the walls, through the attic and then down to the sinks/showers, etc. I suppose the problem of going through the attic is that it gets nearly boiling (even cold water side) before it gets to the sinks in the house.. thus a 'relief' for heat is needed at every sink in the house.. makes since.. but I disabled them (rental house) and will put them back together whenever we leave.

    For now... we have hot enough water to wash the dishes and clothes.. and still retain cold water on the cold water side.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    What you seem to be describing is a "retro circualtion system bypass". It is NOT a high temperature relief valve, it is a thermal valve to allow cool water to flow into the cold line, but shuts off when the hot water arrives at the "tee". When they fail, after a few years, then you get hot water in the cold lines until the "tee" is replaced. You probably have a pump in the hot outlet from the water heater, and what you did made the pump useless because it can no longer operate properly.

  13. #13

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    Quote Originally Posted by hj View Post
    What you seem to be describing is a "retro circualtion system bypass".

    In plain-speak those "T"s (cross-overs) are part of an "instant-on" hot water system.

    Quote Originally Posted by McHub532 View Post
    2. I found these "T"s under each sink. Hot water into the left and up on the left, Cold water on the right and up on the right.. then lines went up to the faucets.
    3. Taking them apart and looking at them.. it ends up if the water got "too hot" it would release pressure and hot water into the cold water side of the T.
    Actually, it's just the opposite - they contain a thermal valve that opens when the hot water side drops below a certain temperature (typically around 95). As you observed, this allows water to flow into the cold water circuit, and ultimately back to the water heater, which in turn brings hot water back into the hot water circuit. When the hot-side valve sees 95, it's supposed to close. But sometimes these valves fail in the open position (hard water deposits), and you see hot water on both the hot and cold side until you run a cold faucet long enough to flush the hot water out of the cold circuit (bad thing if you hop in the shower and the valves are supplying Hot and Hot! damhik )
    Last edited by jeffeverde; 08-10-2010 at 02:05 PM.

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