K-2976 Showerhead water flow vastly lower after remodel adds twin ell

[Xander Fulton]

Searching around on Google for this topic keeps bringing me to threads on this forum, although in reviewing them none seem to be exactly what I'm experiencing. So, time to create an account and ask, I guess!

In a tearing-the-bathroom-down-to-the-studs remodel, we went with a Kohler K-2976-KS-NA (IE., 3/4") Thermostatic Mixing Valve for the shower and tub.

The plumber installed it like so:

For anyone familiar with this (not us! ...at least, not at the time!) This is clearly...wrong. But we didn't realize it until everything was built back out, tiled-in, bathroom, 'finished' and fixtures installed, and we go to use it. And even then, no problem is noticed right away, because mostly we shower, and the shower pressure was *fantastic*. Even swapped out the 1.7gpm shower head with a 2.5gpm we had from before, and the noticeably significant increase in water flow was wonderful.

Then we tried to use the tub diverter. Wow, that...that did NOT work well. It was almost stuck, but by REALLLLLY pulling, we could get it on, and water was just coming out of it full-tilt. Control valve on or off, didn't matter - well, obvious from the above picture. The valve only controls the top port from the K-2976, the bottom port is ALWAYS open, so the only thing keeping the tub faucet from always running was the diverter stop it had. It was always under pressure, though, so an enormous pain to pull open or closed.

Calling Kohler to ask about this, and they point to the spot in the manual for the K-2976 that says only ONE port* should be used in this installation type, and a Twin Ell installed on the tub faucet, with the shower run off of that. Okay, so we give that information to the plumber, they come back, have to tear out the wall from the other side to work on it given the tile, and swap parts around. We did grab this photo while they were working on it...

Sooo...the Twin Ell is in by the tub spout. Which is...good. But the plumbers connected it into the *bottom* port of the K-2976 valve, not the top port as the manual calls for.

For reference - product spec with installation notes (this which note the Twin Ell requirement, and, once we read the doc, noticed that it called for it to be the 'top port' used):
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/K-2976-KS_spec_US-CA_Kohler_en.pdf

...and full product guide:
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/1145568_5.pdf

How big an issue will that be? FWIW, I'm measuring flow of 6gpm out of the tub faucet, which while it feels lower than before (sadly I didn't think to measure flow before, as I had no idea this would require so much back-and-forth trial-and-error when hiring out the work to a long-lived and licensed company in the area) is certainly still in what I understand is acceptable range (particularly for a second floor bathroom). Out of the shower, though (and this with head removed to eliminate any flow control possibility - measuring directly out the spout) is about 0.9gpm, which is...pretty awful, and much less than it was before.

What are my options, here, besides having them tear the entire side of the house apart again? (And if we have to do that AGAIN, what should I tell them is the thing they are doing wrong, because they sure don't seem to be able to figure it out on their own...?)

 

[Terry]

I feel for the plumbers involved and for you. We normally use the bottom port for a tub spout with a diverter. I had no idea that there was a valve that worked the other way around and used the top port for the spout and shower head with a twin el. Yikes!
I can see that even if the plumber read that before he started, he would have assumed he was correct in using the bottom one.

Maybe this will help someone else in the future.

Okay, still reading up on this

This does look way different than most valves. This one looks like you need to slow down and read the manual.

 

[Sponsor]

 

[Terry]

I'm getting even more confused.

You have a two handle tub shower valve where one works as a diverter. Now you run it off of one port and used a diverter spout. So what is the extra handle for?

14.9 gallons a minute through the top port
17.2 gallons a minute through the bottom port.

Looks like what the plumber did the first time.
The more I read up on this, the more confused I'm getting.

Hey engineers, this is a perfect post to comment on. It's 96 degrees in the Seattle area and here I am getting confused by this high volume 3/4" valve from Kohler.

 

[Xander Fulton]

I feel for the plumbers involved and for you. We normally use the bottom port for a tub spout with a diverter. I had no idea that there was a valve that worked the other way around and used the top port for the spout and shower head with a twin el. Yikes!
I can see that even if the plumber read that before he started, he would have assumed he was correct in using the bottom one.

Maybe this will help someone else in the future.

Okay, still reading up on this

This does look way different than most valves. This one looks like you need to slow down and read the manual.

In talking with the folks at Kohler, they've given us some things to try - check the stops for blockage (which did have a lot of junk on the filters), replace the control valve (part 1045321), verify the temperature control, etc. None of which made any difference. It's definitely been an interesting piece of hardware to review and read up on, but I don't know that the issue feels like it is with the valve at all?

I mean, I'm not sure how it's "working", really - with the only connection coming out of the bottom port (which, prior to the last work they did, was always-on, all the time), how is the upper control valve now working, when previously (when it was incorrectly connected directly out the top and bottom) it ONLY controlled the flow to the shower head?

 

[Xander Fulton]

I'm getting even more confused.


You have a two handle tub shower valve where one works as a diverter. Now you run it off of one port and used a diverter spout. So what is the extra handle for?

Ah, no - the top control is the output (on/off flow regulator) only. The bottom control is the hot/cold balance - not a diverter, it's strictly the thermostatic control. So the diverter spout with a Twin Ell is still required to redirect pressure back to the shower head.

I mean, yeah...I have not the foggiest idea why they made a two-outlet system that apparently matters which outlet you connect to, when only one is controlled by the top "volume control valve". How would it have worked otherwise, at all? As initially installed, if there was ANOTHER volume control (only) between the bottom port and the tub faucet? Sure, that'd have solved it - but Kohler doesn't sell such a part!

The guy we had out initially WAS pretty frustrated with it, and now reading through the manuals myself - I get why. But when they came back the last time to work from the outside, we had two guys here and both seemed pretty confident this was how it was supposed to work and put everything back together.

Just...actually using it, it's really pretty far from where we started, and looking at what pics we grabbed along the way, and talking to the Kohler reps (which we've been having 50/50 luck on whether they even recognize the parts we are talking about when giving them the SKUs), it seems something is still kinda off about the whole thing.

 

[Helper Dave]

The "Notes" pic you posted in your first post explain it pretty well, but it is way confusing for something that looks like other shower valves we use every day, but works completely differently.

Either, you install it like they originally did, with a non-diverting spout, and a separate volume control in between, OR you use that double ell out the TOP with a diverter spout.

Silly, but it was wrong the first time, and it's still wrong now (unless they flipped it upside down?).

 

[Jeff H Young]

Follow kohler directions exactly and see if it works. 18 gallons a minute I doubt on 1/2 inch pex depending on a whole bunch of factors but Im thinking your undersize running 1/2 " to the valve
sorry too for all involved , I could understand how a good outfit coulda got caught in not following instructions.
End product should be good , I am disgusted by performance of most tub and shower valves. Kohler usualy are good!

 

[Xander Fulton]

The thing that is throwing me about this is the performance being so low.

Theoretically, without the Twin Ell and showerhead - IE., used as ONLY a tub faucet - this installation is mostly correct. When used ONLY as a tub faucet, the instructions call for the bottom port to be used, and top capped. IE., exactly as it is currently configured.

I assume the reason for the top port being used, rather than the bottom, for a shower installation, is simply to manage the pressure on the diverter better? The Kohler product guide suggests 17.2 gpm (gallons per minute) flow rate through bottom port, and 14.9 gpm flow rate through top port.

But I'm not getting anywhere near that, even out of the tub faucet alone. I mean, if the flow rate was tripled from what I have (measured 6pm out of the tub faucet to the nearly-18 suggested possible), and then the showerhead as well (0.9 to 2.7? Which of course the head then limits, but whatever - that's fine)...

So while the connection is clearly wrong by their instructions for a system with a diverter + Twin Ell + showerhead...it feels like it's wrong in the opposite direction. Given the flow difference out of the two ports from the valve, I'd have expected pressure from the bottom to be *higher* than it should be...

 

[Reach4]

So you have checked that the built-in supply stops are full open. Could there be another set of stop valves before?

I would put a garden hose thread pressure gauge on the drain for the WH. What is the pressure? Run the tub on full-hot. What does the pressure gauge say then? Record the gauge with your phone camera if you don't have an assistant and don't want to run back and forth.

 

[Jeff H Young]

Truth is I never worked out these numbers but 1/2" sounds small for 17 gpm and the valve has 3/4" ports for a reason. If the 1/2' lines are coming directly off a 3/4 or bigger line nearby it might be ok though

 

[Jadnashua]

If that PEX is 1/2" (well, probably even if it is 3/4") there's no way you'd get anywhere near the maximum volume the 3/4" valve is capable of.

 

[Terry]

1/2" PEX to the valve limits what it can do. The valve was designed for 3/4" to the hot and cold inputs.
Even 1/2" copper would have been better than the smaller ID of the PEX. The ratings on the valve were for 3/4" copper.

 

[Xander Fulton]

So you have checked that the built-in supply stops are full open. Could there be another set of stop valves before?.

So I found a hose I could use to run off the stops, directly (removing the stop, essentially, although leaving its filter screen in place).

I find 4.75 GPM coming out of the hot water line at that stop, and 5.5 GPM coming out of the cold water line. Feels like I should be getting more than the 6gpm out of the tub faucet, given from those stops in the valve it's only the thermostatic control and flow control through 3/4" pipe to the tub.

Still, the real problem is the shower, and I'm coming to the conclusion that the main issue is the 1/2" PEX between the twin ell and the showerhead, rather than anything with the valve.

As to why they used 1/2" PEX to the valve in the first place, when this model was specifically intended for 3/4" (and Kohler has a distinctly different model for 1/2")...