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Thread: Hot Water Coming from Cold Water Supply

  1. #1

    Default Hot Water Coming from Cold Water Supply

    I have a contractor remodeling a bathroom in my house. Yesterday he completed the plumbing and put the dent shield around the shower area, nailed the floor down and the wall board is up. He had to relocate the pipes for the sink and the shower.

    After he left yesterday I noticed several things:

    1) When I took a shower in another bathroom last night I had to take the shower with the hot water only and it would usually be scalding, but it was just luke warm and almost cold.

    2) Every time I turn on a cold water faucet, anywhere in the house, within a couple of seconds I am getting warm water, almost instantly. It used to take 30 seconds or so before I would start to get warm water from a hot water faucet. The warm water will run from the cold faucet for about 30 seconds or so and then it turns cold.

    3) When I wash dishes in the kitchen sink I had to turn the hot water all the way on and use no cold water and the water was only luke warm. It is usually scalding.

    I checked the thermostat on the water heater and it is set properly and the water from the water heater is scalding right from the tank.

    They are ready to start tiling in the bathroom today and I think they may have somehow crossed water lines in the bathroom. The toilet supply line is capped, the sink supply lines are capped the shower mixer valve is installed, but the shower head has not been installed. If they crossed a line and it has to be fixed, they will have to tear up the mortar bed in the shower to get at the water lines. They aren't going to be too happy about that.

    Is it possible the shower mixer valve is on and the hot and cold are mixing there? The shower head is capped off and hasn't been installed yet. There should be no water flow through there.
    Last edited by slomo; 12-12-2008 at 03:23 AM. Reason: grammar

  2. #2
    Plumber Cass's Avatar
    Join Date
    Nov 2005


    You have a cross connection somewhere and if you didn't have this before then I would guess it is in the new shower valve...do not allow any tiling to start until this is corrected...if you do you can be 99% sure that part of the shower will have to be torn out...

  3. #3
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007


    If this is what your contractor left installed you need to have him come back right away and install either the cartridge, or, stop valves for the mixer. It is the source of your cross connection. If hot water runs into your toilet when flushed it may crack.

  4. #4


    Okay, that is exactly what it was, the cartridge was no in the valve. When he came back to put the tile down he knew what it was immediately and installed the cartridge and the problem was solved. Thanks for your help.

  5. #5
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default Delta

    There was a small plug with the valve that would have prevented the problem if he had taken the time to install it.


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