Hello, I've got a fitting on the bottom of my tankless hot water heater that is a two piece valve assembly that screws on. Basically it's a large union that has an on/off valve, cleanout/bypass valve, and a threaded hole for the safety pressure valve. The copper solders into the bottom and the top part threads on to the tankless unit which is where the union is. The union has a rubber gasket. When I put this on, I first wrapped the threads with a few wraps of Teflon tape. Threaded on the union receiving end, soldered the copper to the other end, wrapped Teflon tape around the threads of the union and tightened up the union pieces. I added some Teflon tape to the pressure safety valve and threaded it onto the assembly as well. It's a pretty straight forward item. Got it all together, turned on the water, drip drip drip. I see water coming out of the threaded part where the union attaches to the appliance. I see water coming out of the union joint itself (through the top of the union piece rather than the union threads). And to boot, water coming out of the pressure safety joint too! Okay, so I turned the water off, pulled it apart, and did it again with pipe dope rather than tape and tightened it all up really good. Enough that I'm afraid to tighten more although I'm sure the threads are pretty strong. It still leaks, although it's much better than before.

I could probably articulate the problem better if I knew the proper terms for the pieces of the union :) I have this on hot and cold sides of the appliance, less the safety valve of course on the cold side. Same results on both.

Do I maybe have cheap Teflon tape? It's working on my dielectric couplers without any issues. Is my pipe dope crap? It's working on my natural gas lines without any leaks. Maybe I'm over tightening the union causing the rubber gasket to deform? But it leaks above the union too where it's threaded to the appliance. I'm wondering if I need a better thread sealer.

Thanks for the advice!

Did you remove the washers before you soldered the union? It is not the tape but be sure to use at least 3 full wraps of white tape, not yellow.

Yes, I pulled the washers off before soldering. I can't be sure but I thought I used more than 3 wraps of white tape.

Post a pic using "Go Advanced".

The pipe threads will take about 2.5 to 3 turns past finger tight. Yep, tight. That's why pipe wrenches were invented.
One on BOTH sides.

Gas lines require YELLOW teflon tape. The White stuff should not be used for gas.

3 wraps is just the standard minimum, an extra wrap or so does not hurt the seal. Gas pipe teflon is not to be used for water pipes. Water pipe teflon is white, its yellow for gas. What pipe dope did you use?

Thanks BB. Changed my answer to Yellow. See:

Threadmaster Teflon and PTFE Threadseal Tape

Hey KISS, I didn't notice your error, just trying to insure lay3 knoiws there is a difference and used the right stuff. We're good.

Thanks, all. This is water so I used white tape. The dope is teflon pipe dope... t plus 2 or something like that.

Sounds like you used the right stuff but I'm a bit confused, did you dope and the tape the same joint? Overkill if you did that. The dope will let the tape slip and then the tape can actually wipe off some dope. Pickone and try again, use two wrenches like KISS reminds us.

I probably didn't word that correctly. I tried tape first. When it leaked I pulled the tape off. If I missed any it would have been a small thread that was left. After pulling the tape off I used the dope. Does that help?

OK, I understand. Its hard to use words to explain how tight to turn a pipe. Once in a blue moon I have over tightened a connection and actually crack a fitting, bad me. For the sake of time and money I'd pull off the old stuff and solder new fitting.

Trying to put a photo in here. I should have used a nicer camera though because they aren't that clear. But this should help illustrate the point. You see the color band around the top that indicates the hot and cold? Water is coming from there as well as the joint above where it threads on. Plus the safety valve connection point. It's brand new, brass, never used :(

My comments:

You have WAY too much stuff going on in that small space, I'd use 4 unions total so that mess is servicable.

The teflon tape looks like it's bunching up. It should not look that way. It looks as if you didn't put the tape on in the direction of the threads.

I'll bet, if you use 4 unions, things will go a lot smoother.

The pipe has to be tight. A good 2 to 3 turns past finger tight.

Check for any burrs on the sealing surface. When there is a gasket use some plumber's silicone grease on the gasket.

KISS: this is a WATTS or equivalent installation kit designed specifically for Rinnai tankless hot water heaters.

Lay3: you may have deformed the union. Also there may be some debris on inside of the union. The union halves can be hand tight and won't leak. These kits install very easily with no effort at all. We installed tons of them and this is the first time I am hearing about this kind of problems. Maybe you were little rough with it ? Remove the union and inspect it for perfect roundness.

KISS: I think Milo nailed it, it's a fixed assembly recommended by Rinnai. So it's actually a clean setup compared to others I've seen. Also, there is no tape on it. If you look back on the thread you'll read that I removed the tape. You're seeing pipe dope.

Milo: That's about what I was thinking too. While I'm not sure I have the heft to deform that assembly I'm wondering if I tightened the union to the point that the gasket is deformed under the pressure. I'll tear it apart again, clean all the threads, and redo it with a soft hand on the union. I did NOT grease the gasket though and that's a great suggestion.

Post 11, get rid of that union and start fresh, its jacked.

Milo:

Just because it's an installation kit, doesn't make it right for all circumstances. For the amount of time th OP futzed with this project, an extra union would have made his life considerably easier.

When I put in a commercial mixing valve in the house I used 3 unions. Hot, cold and out, so if I want to remove the entire assembly to flush it or to get something out of it, or use gravity and or shaking or take an air nozzle to it, I can. I'll bet if I put it in, I won't have to use it. The extra $ spent is the insurance premium.

Same as, if I want the plumbing movable because of a different water heater and flex connections would be more difficult, I can add a couple more elbows, so I can take any separation distance and I'll have to change one pipe.

Some of the difficulties are: pipe runs against cinderblock wall and other obstructions. Now suppose I had to add a recirculator in the present design. It would require a lot more surgery. If when it was installed, one had the envision of a circulator at a later time, making the pipe longer would be a big help.

One more thing: I found it difficult to apply appropriate pressure on to the union with my wrench since the Rinnai heater mounting seems to be flimsy and appears to be giving away. There is really not enough room to use contra-wrench to compensate for the reverse twist.

In any case, I have to disagree with KISS. It was quite hard to hook up Rinnais before they came up with the installation kit. The kit is exactly what you need to hook it up while maintaining the area clean and compact. It includes shut off valves and drain valves. I think Lay3 did very good by spending extra $100.00 on the kit.

There is definitely a communicatons problem. Let me try again.

The kit is fine and I agree it makes sense to use it. I'm suggesting to add one more union on each line, so the kit can be removed as ONE SERVICEABLE UNIT.

I can see how if you had to replace the unit, or take it off the wall for service this design is nice... with each connection having that union right there. I'd have not considered adding a union to the union in case I had to service the first union. Food for thought although I think that may be a bit over engineered. I think it's roughly 83.4% user error ;)