Water leaks from underneath bath tub when tub spout is connected

If I connect the tub spout to the copper piping and run the water completely thru the spout; water drips to the underneath ceiling. If I disconnect the tub spout so only the copper piping shows, and then run the water completely thru the spout; no water drips from underneath.
Does anyone know what this could be?
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Sounds like you may have a leak in the spout piping. When you install the spout there is then enough backpressure to force the water out the leaking spot. Without the spout, then isn't enough backpressure to force the leak.
Do you have any access to the back side of the tub. Like in a closet or something. You would need to cut an opening. If its in a closet, you can just make a nice panel to cover the cut out.
Darrell

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I agree about the possible leak, but also check to be sure the spout itself is not leaking. Many spouts have an adjustable sleeve in them to adjust for wall thickness and pipe stub length. That sleeve might be leaking, or maybe you just need some teflon tape on the stub pipe threads.
I'd try the teflon tape and inspect the spout, and it's sleeve. If it still leaks, obtain another spout and test that one. If you still got a leak, you probably got a pipe leak. Another thing you might try is to put a cap on the end of the pipe and turn on the water. Then listen for leaking water. If it drips, you got a leak. If not, the spout itself is bad.
If you are lucky, the rear of the tub wall is a closet, where you can make an access panel. Make it permanent. A 16" square of 1/4" plywood and 4 screws are all you need. I never understood why people put a permanent wall behind tub plumbing. Sooner or later, there will be a need to get to that piping.
Mark
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On Thu, 27 Jul 2006 11:31:55 -0500, "Darrell Dorsey"

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I had bought a new spout and applied teflon tape on the pipe threads, and when I installed the spout, it gave the same result as the old spout. One question I have is could the diverter be taking the back-pressure when the water pressure is high and only going through the spout? I did notice water dripping from the diverter handle when the water pressure was high and only going through the spout.
snipped-for-privacy@UNLISTED.com wrote:

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OK, good explanation..... I think you explained the problem. I bet you got a bad seal at the diverter handle and it's running back thru the trim around the handle. I have seen that once. Assuming there is a shower head, there could also be a leak in the shower supply pipe and the spout is causing enough back pressure to cause either the shower supply pipe or the diverter to leak. I'd suspect the diverter first. You might just replace the parts in the diverter. (I assume you have a separate handle type). There is most likely a washer of some type and an O-ring or packing around the stem. That O-ring or packing is likely bad. It's worth the couple bucks to replace those parts and see if that does it. Those parts tend to degrade faster than the faucet ones from being dry most of the time.
Mark

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Thanks to all the input. It turns out it was a worn rubber gasket where the stopper plate is screwed up against. The water backsplash was getting behind the stopper plate and the worn rubber gasket was allowing water thru.
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This sounds very similar to a problem I have keep having. Water from an upstairs bathroom is leaking through my dining room ceiling everytime we use the shower. I have a Delta shower/faucet on the tub. The tub spout has a diverter that you activate by pulling down. When water flows from the spout into the tub no problem. When you pull the diverter, the water comes showering into my dining room through the new hole in my ceiling. The pipe the spout fits over has a brass nut on the end. There is a nylon piece between the nut and the shower wall. The nylon piece moves back and forth on the pipe, but it looks like the brass nut is supposed to hold it in place. This piece has nylon threads for the spout and a rubber gasket. I held the nylon piece against the nut (so it would not turn) with my finger (about 1/2 inch from the wall), then I screwed on the spout. I stopped when it was about 1/2 inch from the wall and turned the water on and then the shower. Water came out from the back of the spout - this is clearly my leak. The water goes through the hole in the wall where the pipe comes through and falls directly down to my dining room. My question is this - if I put teflon tape on the nylon threaded piece and replace the gasket, should this solve the problem? I was also thinking of putting silicon sealer around where the pipe comes out of the wall, so that if it does leak it won't go in the wall and further ruin my ceiling. I am so frustrated with this thing.
I thought I had this problem fixed once before, so I repaired my ceiling only to have it ruined again. For everyone's info, I called Delta and they said this thing has a lifetime guarantee, so they are sending me an all new spout, but that will take another 2 weeks.
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