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?

  • You're using iron pipes to plumb a shower to a water heater? That strikes me as a bit odd ... – brhans May 20 '19 at 20:18
  • Good clarification, thanks. Just the fittings coming out of the water heater are iron pipe so I'm adapting that to 1/2 inch pex. The shower manifold is actually brass, but threaded so I also have adapters from pex there. – Joe B May 20 '19 at 20:25
  • They are both tapered fittings? – Solar Mike May 20 '19 at 20:45
  • @SolarMike The water heater has NPT fittings. the manifold IPS. – Joe B May 20 '19 at 20:55
  • Just asking - fixed several "leaks" due to some over-eager DIY nut not noticing... – Solar Mike May 20 '19 at 20:57

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.

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    I'll try this and let you know how it goes. The fittings are lead-free and I just read that they are sometimes less precisely machined than regular fittings. The same post mentioned that using both solved his leaks. – Joe B May 20 '19 at 22:06

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.

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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?

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