[red86yota]

this is weird.

a few weeks ago, i tapped into my hot/cold water lines to add a feed to a new bathroom. there was one connection in a real tight spot, but i thought i had it soldered up well enough. there were no leaks when i turned the supply on. now three weeks later, it starts dripping like crazy.

so today i cut out the furnace vent tube that was obstructing me before, and made sure to get a nice soldered joint where the leak was.

is it unusual for a leak-free joint to start leaking after a short time? seems weird to me. no one was down there to bang/pull/beat on the piping.

 

[al's sewer]

this is weird.

a few weeks ago, i tapped into my hot/cold water lines to add a feed to a new bathroom. there was one connection in a real tight spot, but i thought i had it soldered up well enough. there were no leaks when i turned the supply on. now three weeks later, it starts dripping like crazy.

so today i cut out the furnace vent tube that was obstructing me before, and made sure to get a nice soldered joint where the leak was.

is it unusual for a leak-free joint to start leaking after a short time? seems weird to me. no one was down there to bang/pull/beat on the piping.

There are several reasons why a solder joint could start leaking after a while it is possible you had some bad flux or you cold soldered (not enough heat) water in the line, soldering on a close system (pressure builds up from the heat and blows the solder out) didn't clean the pipe good enough. as far as it being 3 weeks to start leaking. well strange things can happen with copper fittings. I went into a house one time that was about 20 yrs old and all of a sudden the 90 above the water heater started leaking so I got my tools out and was getting ready to cut the pipe out and it fell apart. the joint had never been soldered and it held for twenty years(go figure). I usually take my chanel locks after I get done with a job and tap on the fittings lightly just in case i missed something.

 

[Ultrarunner2017]

Sure, a cold solder joint may take years to break down, especially if the pipe doesn't get disturbed, and you don't have water hammers, etc.
In electronics, cold solder joints are responsible for at least 90% of component failure in the field.

I'm astonished that an un-soldered copper joint could hold for 20 years without leaking. Was it under normal pressure, or on a line that was kept shut off most of the time?

I'm a little obsessive when it comes to copper sweat. I always double-check that I got everything soldered, and always err on the over-soldered side, which usually leaves blobs of solder around the joints, but I don't want to miss one tiny spot in a tight space, then have to drain and re-solder the pipe later.

I am not a professiona, and only doing my own house, so I don't care that the joints look a bit messy. I have never had a solder joint leak on me. I have had old threaded pipes drip a few times though.

I don't know if you can overheat a joint, but I suppose it can happen, although not as easily as with electronic soldering where there is not the huge copper heat sink that you have with plumbing.

FW