Big Leak from tub water source to shower

[Zoe]

I need help on the best way to proceed with a leak problem. We have a all-one piece shower/tub combo that has a leak going on in the wall when the tub spout is pulled to divert the water up to the shower. We have replaced and tightened the spout and shower arm but it is still leaking through and coming into the kitchen ceiling. It does not leak when only the tub is used, just when showering. I am sure the unit was put in before framing was completed becuase there is no way to get the tub out without cutting it apart. Any suggestions on what the problem might be? Is the stop-check valve likely to leak only when showering?? Because of the small fiberglass opening it is very hard to see back there. Thanks

[hj]

Normally that problem is caused by a cracked thread in the shower arm, but if so it usually breaks off when you try to unscrew it. You may have a bad connection at either end of the shower riser pipe.

[Norcal]

When you pull up on the diverter it creates pressue in the pipe, whereas when the tub is just filling from the spout there is very little pressure in the pipe.

Sounds like the leak is in the pipe between the back of the spout and the female threads (drop ear fitting) that accept the shower arm...likely spots are the elbow behind the spout that leads up to the shower valve, the fitting the connects the spout supply pipe to the shower valve, and the pipe that rises out of the shower valve toward the shower arm.

In any case, it appears that you will have to open up the wall to repair the problem. Always easier from the back side of the shower wall, as you probably observed.

If this tub is on the first floor and you have a crawlspace, you may be able to see the leak from the crawlspace area, looking up into the hole in the floor that allows access to the tub drain/plumbing.

Good luck.