Hidden loop in water supply line

Discussion in 'Remodel Forum & Blog' started by Nathan Davis, Feb 22, 2018.

  1. Nathan Davis

    Nathan Davis Member

    Feb 22, 2018
    Springfield, Missouri
    I’m totally stumped with a plumbing problem.

    Where my main water line enters my basement, it splits into two lines, line A and line B. Line A feeds water to all the internal house fixtures (initially going through the whole house filter and the water softener), and line B supposedly feeds unfiltered and hard water to all the exterior spigots.

    Yesterday, I shut off the water to Line A to replace the whole house filter on Line A. With Line A shut off, I suddenly heard a toilet cycling on. So I checked it and all the other house fixtures, and lo-and-behold I found that water was still feeding to all the house fixtures. So apparently Line B is somehow back-feeding the house fixtures and bypassing the house filter and water softener. For some time now, it appears that hard, unfiltered water has been flowing throughout the house.

    So, I proceeded to shut off Line B, in addition to Line A. That immediately shut off the exterior spigots, and also all the interior house fixtures. Yet, when I turned Line A on, with Line B in the off position, all the interior fixtures received water but all the exterior fixtures were turned off-- just like expected. My paradox is that when I turn line B on, everything gets water, including all the interior fixtures and the exterior spigots. So it appears that the back-feeding occurs in only one direction, with Line B turned on and Line A off. However, back-feeding fails to happen with Line A on and Line B off.

    I spent 6 hours today tracing the plumbing lines to try to see where they might be crossed, but to no avail. At this point in time, I have turned off Line B (the exterior spigots) and turned on Line A (the interior fixtures). At least this will ensure that all the interior fixtures are fed through the water filter and water softener. But with Spring just around the corner, I know that I’ll eventually want to turn the exterior spigots on, and I don’t want the hard, unfiltered water to flow throughout the house.

    Any ideas how this can happen?
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Sometimes there is a bypass near the softener.
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  4. Nathan Davis

    Nathan Davis Member

    Feb 22, 2018
    Springfield, Missouri
    Right. I checked and that bypass is closed.
  5. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    Turn off the valve to the water heater. Do you still get the crossover?

    How about opening an outside spigot with B off. You, and your best-hearing assistant, go around to the various faucets and listen for flow. Maybe put your ear to the faucet. Maybe just listen from beneath. Maybe feel pipes.

    In particular, check the kitchen sink for the possible crossover.
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