Leaking brass npt fittings on new Grohe shower install

[cdnhx]

Hi,
I'm building a new bathroom. I ran PEX for supply. The shower uses a Grohe thermostatic valve that is external to the wall (on the finished side of tile) and it uses brass fittings that screw in to a FNPT fitting that will be inside the wall.

So I have to go from 3/4 PEX->1/2 FNPT->Special Grohe fitting. I can't go directly from 3/4 PEX to 1/2 fnpt so there's an extra fitting in between.

The way I have things connected now is:
Fitting 1: 3/4 PEX to 3/4 FNPT
Fitting 2: 3/4 NPT to 1/2 FNPT
Fitting 3: Grohe Fitting into 1/2 FNPT above
Fitting 4: 1/2 NPT plug for testing

I'm trying to ensure no leaks from the threads of NPT fittings prior to closing up the walls. I've got my cold working just fine. I've turned on the water and left it for a couple hours without any leaks. My hot water is a problem. I've got a very slow drip leak.

I am using teflon tape on the threads (wrapped 3-4 times around). I've tried redoing it a couple of times. Each time it starts leaking after some time. I've got them quite tight using 2 wrenches (about as I can without moving to longer handles. The threads are not bottomed out though. There's maybe 3 threads still exposed.

I've read that with brass fittings you can actually over-tighten. Given lack of experience with these types of fittings I'm not sure at what point that would occur.

I'm thinking of getting a new plug to test that. maybe this one is just too far out of tolerance from manufacturing.

Any advice? Should I get some bigger wrenches and tighten until bottomed out? Am I not wrapping with enough tape? Should I combine with some liquid sealant? How long should I leave water one to be confident I won't have leaks at some point in the future?


Thanks.

 

[WorthFlorida]

Once in a while a little pipe dope is needed. Sometimes too much tape is not good. With brass it's a matter of feel and experience to know when it is tight enough. With all the fittings I think you know when to stop. Brass is soft and too tight and you can distort the threads.

https://www.homedepot.com/p/RectorSeal-T-Plus-2-1-75-oz-Non-Stick-Thread-Sealant-23710/100116773

 

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[Reach4]

I am using teflon tape on the threads (wrapped 3-4 times around). I've tried redoing it a couple of times. Each time it starts leaking after some time. I've got them quite tight using 2 wrenches (about as I can without moving to longer handles.

Get longer wrenches, or put a pipe over the wrenches as an extension.

If you want to take the joint apart, use PTFE tape and pipe dope when you put the fitting back..

 

[Jadnashua]

Tighter will probably work, but tape and pipe dope (or pipe dope itself) will seal it. Sometimes, the threads on fittings coming in from China are crappy - incorrect depth, dull cutter so that they are not smooth. It’s also possible that there is a microscopic hole in the fitting, but that’s rarer. More common in a cast fitting, but still not common.

 

[Fitter30]

Any brand of anaerobic pipe dope is my go to.

 

[Terry]

Is the valve you have similar to these Grohe valves?
I'm normally three wraps with tape and pipe dope over that.