Baffled - 1/2" NPT connection leaking at back of frost-free faucet

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Old 05-17-13, 03:09 PM
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Baffled - 1/2" NPT connection leaking at back of frost-free faucet

We developed a leak at our frost-free faucet, inside the house where the faucet connects to the water system. The faucet seems to have a standard male 1/2 inch pipe thread.

The connection that failed was a poly-B 1/2" pipe fitting, and inside it was a tapered rubber gasket sealing between the poly-B tube (about 12mm diam inside the fitting) and the inside of the faucet's 1/2" NPT.

The plumber came out and replaced the poly-B with PEX, and put in a new connection which is a copper or brass female 1/2" NPT. The metal fitting was soldered and crimped to 1/2" PEX. So now the seal is on the outside of the faucet's pipe connection instead of the inside. The plumber told me that he put on a generous amount of Teflon-loaded goop.

The problem is that the new connection leaks slightly, producing at most a drop every few minutes. We notified the plumber and he came out and torqued the fitting about a half turn. That should fix it, I thought.

But no, the connection is still leaking, and at about the same rate as before. I can't believe it. How is the water getting out?

I would rather not call the plumber out a third time for this. Maybe I can solve this myself. But before I start cutting and crimping, I wanted to see if any of you have ideas.

- Should I use an O-ring inside the male 1/2" pipe fitting?

- Should I remove the goop and use teflon tape instead?

- Should I revert to a tapered gasket mating to the inside of the 1/2" fitting?

- Should I inspect the pipe thread for faults?

- Would another 1/2 turn do it?

- Is there something else I'm overlooking?

Any help appreciated.
 
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Old 05-17-13, 08:42 PM
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Picture

Picture attached -- might help clarify the situation.

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Old 05-17-13, 08:58 PM
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I would rather not call the plumber out a third time for this
You paid for the work..... it should be done to your satisfaction.
More goop doesn't give the fitting more leak resistance.

Pipe threads are tapered and normally seal with a minimum of teflon tape or compound.

In your case I'm wondering if that crimped on fitting is too short and not allowing the faucet to screw in far enough for the tapered threads to work.

In looking further at your picture I think your frost free hose bib is cracked or is leaking where I drew the red arrow.

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Old 05-17-13, 09:36 PM
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Thanks, PJmax.

That is very observant of you to notice that mark on the hose bib. But I don't think it is a crack. It is the very bottom of the bib and the moisture that is leaking out collects there and leaves that mark. I cleaned it up a bit with steel wool... see pic. I think it is OK.

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But maybe there is a defect in one of the threads of the 1/2" pipe connection. I guess the only way to know is to remove it and inspect it closely.

I was thinking that putting a rubber washer or O-ring in there when reassembling might help.

IMHO the plumber did what he could. There must be some preexisting condition that is not their fault causing the slow leak. On the third trip they may come to that conclusion... then they would probably have the inclination to do something drastic to fix it once and for all, and charge me for that extra work.

The reason I mentioned the plumber bragging about his Teflon goop is that the comment seemed unnecessary. As you say, tapered joints shouldn't need that... so why did he mention the goop? Maybe he noticed something that he thought extra goop would fix.
 
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Old 05-17-13, 10:13 PM
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There is no seat inside that fitting so a gasket or O ring won't do anything for sealing.
 
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Old 05-24-13, 09:02 AM
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OK, I removed the old fitting and replaced it with a rubber-lined brass fitting secured by a plastic part that is hand-tightened. This fitting is apparently designed for attaching to frost-free faucets. See picture. Worked great. No more leak.

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I examined the old parts. They were fine... except that the female 1/2" pipe fitting was a bit shallow. This might have been making it hard to tighten, and allowing water to get past the threads -- as suspected previously by PJmax.

This also suggests the plumbers did not do a good job. But I bet if I had asked them to come out a third time, they would have wanted to replace the frost-free faucet, and it would have cost me $300.

Doing it myself cost $3 for the new fitting, plus a couple dollars gas to get it.
 
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Old 05-24-13, 10:01 AM
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To solve the mystery, the female threaded couplings are notorious for having little burrs in the treads that prevent you from tightening them enough. The copper is also relatively soft so defects in the treads occur or it gets bumped during shipping. I usually sit Indian style on the floor with the box full of fittings both male and female and do combinations until I find pairs that marry together nicely. So I too learned the hard frustrating way.
 
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