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Thread: Problem sweating second joint on a fitting

  1. #1

    Default Problem sweating second joint on a fitting

    It's been a while since I've sweated copper pipe, and I'm running into a new (for me, anyway) problem...

    I assembled the whole thing, cleaned and fluxed, and started sweating the joints. I noticed that the first joint on a fitting typically went very well, but the second one often didn't. The solder just wouldn't flow right.

    I think what was happening was that the flux in the second joint of the fitting was just getting oxidized out while I was sweating the first joint.

    How does one avoid that, especially on smaller joints such as couplers?

    And a second question...how likely is it that a joint that passes muster when first put under pressure will fail sometime later? Can I be fairly certain that a joint passing the initial pressure test will remain good?

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


    Practice...is the tubing open to the air some where so that your not trying to solder a closed system...?

    You are most likely getting the fitting to hot....try heating the whole fitting at the same time..

  3. #3
    Master plumber Jay Mpls's Avatar
    Join Date
    Sep 2008


    It is always my luck after the house has drained down I have to outlast or outwit water from something.Kind of sounds as though you *may* hae been fighting water.
    Every now and again I have expansion from the water heater to contend with.
    On a short closed system you may have been fighting pressure from your own heat.
    Beyond that, it's all in the preperation!

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default solder

    Do not stop after each joint. Do one, usually the largest, then the next, and so on. For a vertical line do the lower joints first and then work upward.

  5. #5


    Thanks all for your help.

    It turns out the issue was flux. I originally bought a "kit" containing some solder, some flux, and a flux brush, and the flux was obviously not very good. I ran out, went to the store to get some more, and the guy there said "don't use that junk..try this!". And "this" worked wonders. Every joint I sweated after that worked perfectly (and I don't think my technique had miraculously improved, either!).


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