Shower head leaks when tub faucet is open

[Brad Borch]

When we built our home about 10 years ago we used a standard Moen combo tub/shower controller, but didn't include a shower for the tub. When I went to tile the tub, I also decided to add a shower. So I ripped out the backer board and then discovered the plumbers had sweated a plug into the top of the controller where the shower pipe would go.

No problem, I thought, I'll just tee off the bottom pipe that goes to the tub faucet, run a pipe up to the shower head, and the shower will work when the tub faucet diverter is pulled (which is how I understand the system works). Now, however, water still drips out of the shower head even though the tub faucet diverter isn't engaged. The pipe going to the faucet is 1/2". Do I need a larger size? Is there something going on with the controller that I'm not aware of?

 

[Terry]

Did you use PEX to the tub spout? That would force water to the shower head.

No PEX or CPVC to tub spout, or Sharkbites.

 

[Sponsor]

 

[Brad Borch]

No, it was orginally was plumbed with 1/2" copper, I added a sharkbite union and the rest is 1/2" PVC. But the PVC to the shower has to go through a tee and two elbows, so I figured the pressure would be greater getting to the shower than to the faucet.

 

[Terry]

The Sharkbite is a restriction, and so is the CPVC.

Copper to the tub spout. All the way.

 

[Brad Borch]

But it's a restriction before the tee to the shower leg.

 

[Brad Borch]

If I pull out the cartridge can I unsweat the plug without damaging the valve?

 

[Brad Borch]

Also, I used a shower head elbow to make the tub faucet more stable, was that a bad idea?

 

[Terry]

Any restriction on the way to the tub spout will push water upwards.
That's why they say 1/2" copper or full size pipe.
CPVC is not full sized, nor is PEX. And any fittings that use PEX are even worse.

If you pull the cartridge, you may be able to unsolder the plug. You will still need unrestricted piping to the spout.

 

[hj]

You CANNOT "tee off the drop to the spout" and expect the shower to work properly. You either need a "twin ell" at the spout or connect the shower to the top of the valve where it belongs.

 

[Reach4]

Brad, could your tub spout has more backpressure than most? Do you have a make and model?

Is your spout easy to pull off and inspect? Maybe try running the water with the spout off, as a test.

 

[Brad Borch]

Thanks for all your help. I pulled off the tub spout and there's still too much back pressure.

Stupidly I tiled everything before testing... the good news there's a shower on the other side of the wall, and I was planning to tile that, so I just pulled off the cheap paneling and unscrewed the cement board, and now I have access and will do it right.

There are PEX supply lines, do I need to disconnect them from the mixer to unsolder the plug at the top?

 

[Reach4]

I suggest a photo.

I don't know about the PEX removal.

 

[Brad Borch]

The second image shows my attempted fix, with a sharkbite coupling going into the 1/2" CPVC, to a tee which goes down to the tub spout, and loops up to the shower head. There was too much back pressure, which drove water up the shower head even when the tub spout diverter wasn't set.

So I need to remove the plug at the top that was sweated in (first pic) and run the lines as designed. My question is, when I unsweat the plug at the top, will the PEX supply lines get damaged?

 

[Reach4]

Informative photo.


If you re-do it with the stuff shown in brown with copper, and the stuff in yellow as anything, I think the problem would go away.

 

[Terry]

I doubt that you can unsweat the threaded plug at the top. You would like a new valve anyway, right?

 

[Jadnashua]

Take HJ's suggestion and pick up a twin-el. The larger port goes to the tub spout (no restrictions can exist to it), and the smaller outlet is then run to the showerhead. But, if you do want to try to remove the plug, definitely remove the pex first (and cpvc).

Many valves can be restored to like new condition with just a new cartridge and pretty trim, but a really old one may not have the required safety anti-scald functionality, which, if the remodel was inspected, would be required.

Using pex or cpvc as supply lines to the tub will slow the fill rate verses using copper. Using a pex connector with a crimp verses the expansion type restricts things even more.

 

[Brad Borch]

Thanks, I think I'll do the twin-el solution, the valve is only ten years old, and I recognize un-sweating the plug at the top is not likely to go well.

 

[hj]

correction about the twin ell openings. The "large" opening is for the spout. The front 1/2" opening connects to the valve and the rear one goes up to the shower.

 

[Brad Borch]

So I went back to my basic physics -- pressure is inversely proportional to surface area (in a gas, and dynamic liquids are similar). So I just sweated on a 1/2" to 3/4" adapter, added a 3/4" x 3/4" x 1/2" reducing tee, fed the tub spout with the 3/4" and fed the shower with the 1/2", and voila, no more shower dripping, even though the tub spout with diverter open only has about a 1/2" output area.

Thanks everybody for your input!