What to try next when pipe joints leak with both thread sealant and with teflon tape?

Question

I am plumbing a couple fixtures (a water heater and a shower) with pex and a few threaded fittings (at the heater and shower fixtures only). At first I used teflon tape (3-5 turns in direction of thread), but all the threaded joints were leaking. So I removed all the tape and replaced it with some T2 thread sealant I had laying around. Again, all the joints leaked and some worse than before.

I've also played with different levels of tightness to no luck. Am I missing an essential step in my joins?

What other solutions exist to seal threaded iron pipe or brass joins?

Answer 1

Try a hint of pipe dope in the thread valleys with 3-5 layers of PTFE and tighten in stages over the course of 30+ minutes.

Relevant backstory:

I just installed a new water softener and had to use a 1" NPT female to 3/4" pex barb connection between the house plumbing and the resin tank's yoke connection. I tried PTFE tape first and it leaked so I tried pipe dope and it leaked worse. I cleaned it all up and tried PTFE again (though there was some pipe dope residue which might've helped). I went a turn past hand tight and it leaked so I tightened it up. I repeated this 5 or 6 times until I tightened it just enough to stop the leaks. Don't go too tight, because in my experience if you go too tight you can leak. There seems to be a sweet spot. Three days later it's still not leaking.

Answer 2

Never put pipe dope on the threads of the female fitting. It will allow pipe dope which is not water soluble to clog aerators and put contaminants into the water. If the threads on both male and female fittings are threaded correctly and with sharp dies the threads should hand fit up to 2-1/2 threads. Pipe dope and tape can be applied in excess. 4 wraps of tape on the male threads with a quality Teflon tape is sufficient, wrapped over itself clockwise looking from the narrow end of the threads. Or paste pipe dope should be applied to the first 4-5 threads of the male threads and not gooped on. No pipe dope whether tape or paste should get inside of pipe. Not a good thing. Tighten the joint until it is snug, not until it can not be tightened any further. It is a feel or touch thing you will acquire with practice. Turn on pressure whether liquid or gas and test for leaks. If there is a leak and you didn't tighten the joint so tight you hurt yourself you can tighten it little more to stop the leak. If you tightened it so tight there is no more tightening you must untighten the joint completely and start over. PITA. Have been doing this for 48 years and has never failed if threads are good quality threads. Problem today 50% of threads are crap. Remember the fit up. If too loose or too tight get rid of bad fitting.

Answer 3

Thread sealant often has a shelf life of only a few years. Buy new thread sealant.

Wrap a few rows of teflon tape on the male threads, and then apply pipe thread sealant on top of the teflon, then also put some pipe thread sealant into the female threads and wipe the excess away, then install and tighten fittings.

This was the only way I was able to get 1" NPT fittings to stop leaking on a water softener install. Teflon or pipe thread sealant alone did not work.

Answer 4

After trying the above and reapplying, I came across a forum post recommending some blue pipe dope and that worked really well.

Here's a link to the one I used: https://www.amazon.com/Rectorseal-31631-Tru-Blu-Pipe-Thread-Sealant/dp/B0012YO0Z4

I don't know what the difference is between the two, but I'll be using this one from now on.

Answer 5

Are you using inserts into the end of the PEX pipe before putting on the compression fittings? I presume that's what you mean by 'threaded' - they have an olive between the two parts?