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Our upstairs bathtub has a small leak inside the wall that over time softened the ceiling sheetrock below. After removing the sheetrock we tested the shower, and it's weird -- it leaks about 1/4 cup ONLY when someone is IN the shower, and ONLY when the shower is turned off. If we run the shower with no one in it, it doesn't leak no matter what. While the water is running, it's fine. Only leaks with someone in it and only at the moment it's turned off.

I've removed and re-caulked the tub spout/diverter and the valve decorative flange.

It's a 20 year old Moen single valve.

Any ideas?

  • Is there a possibility that the shower/tub enclosure is not fully supported by the building structure and that flex is placing a stress on the incoming plumbing? It could be that some of the pressure fittings only leak when stressed. – Michael Karas Apr 27 '15 at 11:58
  • Possible, but it's a very well built custom home. Certainly worth exploring... – Arnie Apr 28 '15 at 13:39
  • Can you tell whether leak is coming from the drain or the supply pipes? – feetwet May 3 '15 at 3:32
  • Finally cut the wall open and found it was coming from the overflow. When someone is standing in the tub and turns off the faucet, the diverter released a flow of water that traveled under the spout and down into the overflow. The weight of the person was deforming the tub side slightly, as Michael suggested, creating a gap due to an old stiff gasket. Replaced the gasket, all is well. Thanks for your thoughts! – Arnie May 4 '15 at 6:20

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