I have a 3/4" copper Nibco union that has an extremely tiny leak on the side of the nut closest to the threads. I saw a miniscule bead of water on the joint but it must have taken hours to form since I cannot get it to bead again. However, putting a small swab of toilet paper to it I get a tiny hint of moisture.

I made the connection 2 months ago. I put dope on the mating surface and threads before doing so and tightened it with a 12" crecent wrench and a 12" slip joint plier. Its in a very tight spot where two pipe wrenches are hard for me to maneuver.

Anyway... my question:

Am I asking for trouble completely loosening the nut and trying to retorque? Are you able to remake a union in this fashion or is replacement needed?

Or should I try to tighten without redoing it?, (I doubt I can get it to budge further, it wasn't moving when I finished making it up originally). If I do this, should I do with water on or off and system drained?



Im really frustrated and would really like some overnight calcification of that joint to stop this tiny leaker!!!



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you could try a few wraps of teflon tape. apply it to the side that the big nut is on. wrap it around the tapered male end of the union. sorta form a thin teflon gasket between the two mating surfaces.

If this union is a soldered in model, Nibco had some defective ones, that had bad mating surfaces(I had 4 of them that leaked) and no amount of tightening would make them stop leaking. The ones I had leaked a lot, but I would replace the one you have.

Take the union apart and clean all the gunk from the mating surfaces. The machined surfaces are designed not to use anything between them and you may be causing a minuscule gap.

thanks for the tips, I knew those were my options though.

I waited overnight and there is no visual sign of moisture on the joint.. no bead, no drip nothing. However, if you put a small piece of toilet paper to the joint, it picks up a pinhole size circle of moisture.

What do you guys do when they are this tiny? Do I suck it up and risk disrupting the rest of the joints close by reefing down on it again? Its the kind of thing where if a plumber caused this leak upon installation he would never it on the job and it wouldn't be detected until he was home. warm and snug in his bed.

I do remember when installing I had 2 unions. I inadvertently used the nut and female portion of one of the unions with the male end of the other union... Is swapping them like this causing my leak perhaps?



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i would still try a few wraps of teflon tape on the male end. wrap it around the end and have it overlap the end slightly so it forms a thin gasket.
remember, there are many, many places in plumbing that rely on a gasket squashed between 2 mating surfaces.
faucet and toilet connectors are the most common. water meters have union ends with rubber washers in them. they seal and last for decades.
you are not re-inventing the wheel, you are improving on it.

A 12" Crescent wrench and Channlock pliers are NOT enough to tighten a 3/4" union. You need bigger wrenches, ( I would use a 14" and an 18" pipe wrench to do it), and just retorque it without taking it apart.

i think somewhere he states that he has limited access and is using the biggest wrenches he can fit into the space.
hj, an 18" wrench on a 3/4 " copper union??

I got to thinking the same thing. THis morning I was able to manage a 14" pipe wrench and gave it a tug with the water still on. The leak got worse for a second and then has seems to have stopped.(knock on wood)

Being a novice I was thinking since I couldn't go further with a 10" adjustable (yes 10 not 12) and 12" channel locks that I wouldn't be able to go more with a pipe wrench. I think I could even go tighter with the larger wrenches if needed.

Thanks again (and as usual).

p.s.- I do have my now deceased granddads 18" ridgid if I need to go further.

pps- Do you think that tiny leaker was there from day 1 or developed over a period of 2 months?



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unless there was an external event such a vibration which could make a union leak, the leak would have been there since day one..

I only have one 14" one.

It would have to be SERIOUS vibration to loosen a union which was properly tightened.

It has always been there.

you have to define'properly' tightened.
if you tighten a 3/4 " copper union with 18" wrenches, it would take magnitude 4.9 tsunami to loosen it.

In that case it is "proper" if it loosened, it would be "improper".