Leaking shower......stumped

I noticed my shower was leaking when I saw water on the lower wall in my living room. To try and find the problem I didn't use the shower for 3 months to let it hopefully dry out.
I then did the following to attempt to find the problem.
To test the drain I ran water down it from an outside source for 10 minutes, no leaks. To test the pan I plugged the drain and filled (outside source) the bottom of the shower as high as I could, about 5 inches, without it spilling out and left it for 20 minutes and still no leak. To test the incoming water pipes I ran a hose from the showerhead pipe to my backyard and ran the hot and the cold water for 10 minutes each, individually, and at different volume, still no leaks. I am stumped. Thanks
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CP wrote:

The pipes could leaking inside the wall when you turn on the shower.
TDD
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It could take a substantial amount of time/showers before the leak is evident. The water may need to saturate a "local" area before you see the water elsewhere.
Do you have access to the pipes from inside the wall? Can you see the diverter/valve from the back?
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CP wrote:

What is above the wall between the shower and living room? Attic? Check the roof? Tile on wall in shower? Grout deteriorating?
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You pretty much did the tests I would have done.
You might consider re-doing the pan test. Mark the height of the water & leave it overnight.
Depending on how the valve set is designed you might be getting a valve stem leak that leaks into wall cavity.
Remove the valve set trim & maybe you can get a look?
Open up the ceiling / wall below the shower area to get a look?
cheers Bob
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Is it a tiled wall in the shower? A surprising amount of water can leak through cracks in the grout. Test by directing water at the wall with the shower head or a hose. --H
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wrote:

I totally concur with small gaps in the grouting being able to channel LOTS of water where you don't want it.
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Could it need your weight on the pan before it leaks? maybe a crack opens up with the weight

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Don & Lucille wrote:

Grout could have gone south and need replacement or resealing. Seal around knobs could be bad, too, and only let water in wall when it bounces off a person standing in shower. But like the other guy said, I'd try the full-pan test again with weight in there, like a person or 2-3 concrete block sitting on an old towel. Moving weight is a better test than static weight. Does the wet wall in living room directly abut shower, or is it a floor or half-floor lower down? If drywall is mushy, you will end up cutting it out to replace it eventually anyway- may as well open it up now so you can get a good look.
-- aem sends...
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CP wrote:

construction and a shower guy told me it can take some time for water to penetrate before leaking starts. As others suggest you will probably need to reveal bottom of pan.
Couple of years after pan was redone, leaking started again as walls were going. Cheap builder had not used cement board or water proof drywall. Ended up having whole shower redone properly. Been over 30 years and no leaks.
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I normally have the furnace fan ON all the time, but when we moved out it was off. We soon had all kinds of pinhole leaks in copper tubing, in and out of the wall. I guess they just corrode and get holey wherever they may be.
John

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It looks like maybe you posted the question and then never came back to read the answers.
Water could be getting on the bathroom floor when people shower and then going down through the floor around the outside of the shower.
Or, water could be getting in behind the valves and/or diverter where they come through the shower wall. They may need to be re-caulked.
Or, it could be what others said about going through cracks in the grout, being a small leak in the shower pipe behind the wall when the shower is on, etc.

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The smallest crack in grout will do it, I had it happen and had a worker find all cracks, dig them out and redo it.
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