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Thread: Hot Water in the cold water pipes

  1. #1
    DIY Junior Member dvandruff31's Avatar
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    Default Hot Water in the cold water pipes

    When I use the hose or sprinklers outside, the faucets (double handle) Shower (single handle) and toilets start getting only hot water going through them. Nothing in the system has been changed, this problem just kind of came up. Can anyone give me some in site into why this has occurred and what I can do about it?
    Thanks so much
    David

  2. #2
    DIY Senior Member Smooky's Avatar
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    Sounds like you have a cross flow somewhere. Do you have a washing machine Y mixer hose? Is there hot and cold water at the outside hose bibb? Turning on both hot and cold at the spigot and having a nozzle turned off at the end of the hose can cause a cross flow. Sometimes shower valves can malfunction. Do you have a hot water recirculation pump?

    http://www.toolboxsupply.com/y-water...-hose-3-8.html

  3. #3
    DIY Junior Member dvandruff31's Avatar
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    The hose bibb is only cold and the washing machine to my knowledge has no "Y" mixer hose. Unless the Y is inside the machine and you're unable to see it on exterior. No recirculation system, just the regular old 45 year old standard plumbing. The shower valve is 6 or so years old. Could it be the problem even when it's not running and turned off? It's very frustrating as this only started to happen 6 or so months ago. I really do appreciate your assistance.
    David

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    DIY Junior Member John28's Avatar
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    Is the hot water just for awhile, then turns cold after running a bit? If so, it's possible water lines somewhere could be absorbing heat from a source when sitting stationary. Or if lines are exposed or within a cavity where the sun shinnes directly on them can heat it up some like a greenhouse effect?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Some single handle valves can allow a cross-over between the hot and cold when off (not all). If it allows it, try turning the handle to full cold and see if you still have the problem...if so, you've identified the problem child.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Junior Member dvandruff31's Avatar
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    I don't believe it's absorbing heat, it's under a raised floor and the water is hot, not just warm. Honestly, if the spigot outside is on and the faucet inside is already hot I can't get cold water out until I turn the spigot outside off. My biggest concern is that the toilet is going to crack.

  7. #7
    DIY Senior Member Smooky's Avatar
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    Do you have access to the water lines to the shower valve? With no water running anywhere in the house all water pipes should cool down to room temperature. But when you run a cold faucet such as the outdoor spigot it will suck the hot into the cold if there is a cross flow. If the cross flow is a the shower valve the hot will flow into the cold at that location and then both water pipes at that location will become hot. If you turn off the cold spigot and go run a hot water faucet somewhere else in the house the shower valve should start to turn cold because the hot water has less pressure and the cold water will began to cross into the hot water . If you can hold on to the pipes before they go into the valve you will be able to feel if the pipes are getting hot on the cold side or cold on the hot side. The shower should not be on during this test.

  8. #8

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    could be a broken dip tube in cold supply to water heater. turn the outside hose on and see if the cold feed into the tank gets hot, if so it is pulling hot water directly through the tank and not a cross connection further down...if the lines are accessible so you can trace them it is easy to find your problem.... run a cold tap with hot water coming out of it (your problem scenario) then follow the cold supply from that point backwards along the cold supply and see where it turns from cold to hot and that will tell you where the problem is occuring

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Broken dip tube would NOT cause that problem. If anything it limits the amount of hot water you get.
    Licensed residential and commercial plumber

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