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Thread: Losing water pressure = leak?

  1. #1
    DIY Junior Member jptemp's Avatar
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    Default Losing water pressure = leak?

    I am stumped. I have an apartment where the bath and kitchen fixture and water heater are all fed by one 1/2" line with a ball valve. Shut off the ball valve and no water goes to any fixture.

    I shut the valve off, and the next day I turn on a faucet and there is almost no pressure. Shouldn't the lines stay pressurized over night? There are no water leaks that I can see. None of the fixtures drip. the pressure relief valve on the water heater does not drip.

    It seems impossible.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    I would not expect to find much in the way of residual pressure. A few drips in the toilet tank and you would never notice. If you want to get serious about your "testing" you could put a pressure gauge in the line and see what happens.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Anyone flush the toilet? Since the pipes don't really stretch at the pressures in a normal home, that leaves maybe the rubber/plastic hoses to the faucets that can act like a bladder to help hold the pressure. All it takes is a VERY small amount of water coming out somewhere to relieve the pressure. That could happen just by the water cooling off, especially if you turned the WH off, since the cooler water is more dense (i.e., takes up less space). Do you have an ice maker on the frig?
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member jptemp's Avatar
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    Quote Originally Posted by jadnashua View Post
    Anyone flush the toilet?
    No, the toilet was out do redo the floor.

    Since the pipes don't really stretch at the pressures in a normal home, that leaves maybe the rubber/plastic hoses to the faucets that can act like a bladder to help hold the pressure.
    About half of it is type A pex and half copper. Would that do it?

    All it takes is a VERY small amount of water coming out somewhere to relieve the pressure. That could happen just by the water cooling off, especially if you turned the WH off, since the cooler water is more dense (i.e., takes up less space). Do you have an ice maker on the frig?
    Water heater was on and no ice maker.

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    DIY Junior Member jptemp's Avatar
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    Quote Originally Posted by cacher_chick View Post
    I would not expect to find much in the way of residual pressure. A few drips in the toilet tank and you would never notice. If you want to get serious about your "testing" you could put a pressure gauge in the line and see what happens.
    The toilet was out at the time. I could put a pressure gauge on the kitchen sink, all I would need is an adapter to a male garden hose thread. I suspect the pressure will drop from 50 to around 10.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Why are you worried about it? Unless the pipes are not all visible, you obviously do not have a leak. The pressure could drop for any number of reasons, but unless it were ZERO, a leak could not be one of them.
    Licensed residential and commercial plumber

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    DIY Junior Member jptemp's Avatar
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    Quote Originally Posted by hj View Post
    Why are you worried about it? Unless the pipes are not all visible, you obviously do not have a leak. The pressure could drop for any number of reasons, but unless it were ZERO, a leak could not be one of them.
    I'm worried about it because the pipes are not all visible and it might be leaking somewhere inside the walls, creating mold, wood rot, etc.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Just the simple act of the house dropping in temp might would make the pressure change. Colder water shrinks until it gets to about 34-degrees, then starts to expand again (the reason ice floats).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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