New bathtub diverter spout drains back into wall

Question

I replaced my old diverter spout with a new one (both Delta), and I've found that the new one will leak water back through the hole in the wall if the diverter is switched off while the shower is running.

If I first turn off the water pressure and then push in the diverter, no problem. So, seems to me that the issue has something to do with the onrush of water when the diverter is switched off while under pressure. I'll just mention that our water pressure is typical (wimpy) for Southern California.

The new spout has a copper piece that screws onto to the water supply from the wall:

...and then the spout screws onto that until it's flush with the wall (there is no set screw).

If I block the spout with my hand and try to blow air through it from the back (with the diverter off), I'd expect flow to be blocked. Instead, I can feel air escaping out of the holes in the back.

What puzzled me when I was installing this (there were no instructions) is that it doesn't seem to be designed to seal against the wall or prevent water from getting into the outer body of the spout.

Anyone know what I'm doing wrong? Any advice?

I need to finish this up so I can repair the drywall in the downstairs ceiling.

Cheers!

Answer 1

How do you know water it leaking back into the wall. I can't quite see from your pictures, did you uses plumbers tape between the copper threads and the new brass piece (three times around, in the direction of the threads)?

I've installed some of these spouts. They never have a set screw. Once the rubber seal is well inside the spout water shouldn't get back there, unless there is a leak between the copper and brass.

The diverter isn't air tight. When water hits the diverter it gets pushed tight making a water tight seal, your breathe can't push it enough to make that seal.

Answer 2

I know of no tub spout that is, or is designed to be, watertight. It is the hole in the wall from which the spout supply pipe emerges that needs to be sealed. This can usually be accomplished with caulking around the pipe, but pointlessly large holes such as shown in poster's photos make that extra hard. Better tile supply vendors sell "rubber" gaskets that grip the spout pipe snugly, but that is something that must be installed prior to the finish surface.

Answer 3

Something is very strange with this design. If water gets between the threads with the PTFE tape and the O-ring, how would it get out? The only way this design can work is if the O-ring makes a complete seal and water never gets past it.

It may be that the front flat of the threaded area is supposed to be tight against the plastic. The strands of PTFE are interfering with that.

Take the PTFE tape off the threads, put silicone grease on the O-ring and thread the spout on firm. The threads are not designed to hold back water so no sealant is needed on them. Those threads are designed to hold two other sealing surfaces together and the PTFE is interfering with tightening the spout as it should be.

Look inside the spout to see if PTFE tape has gotten into the O-ring sealing area and if so remove it. It would interfere with the O-ring sealing.

EDIT

The brass fitting screws into a fitting which is soldered (sweated) onto the copper pipe. The threaded joint must be sealed with pipe dope and/or PTFE tape. I personally prefer pipe dope. This joint might be poorly sealed and leaking. If you think it might be leaking, unscrew this joint, clean it out and apply good quality pipe dope or PTFE tape, then reassemble.