Elusive Shower Leak

[fsrph]

Hi,

I have a problem with a leak in the shower. This problem is elusive and driving me crazy trying to fix it.

The history -- Older house, 2nd floor bathroom with tub shower combo. Separate knobs for hot and cold water. This is not a gushing leak but more a seeping into the beams above the lower level kitchen. I know this is happening because four kitchen ceiling blocks have been removed about 9 months ago. This was done by a plumber to install a new bathtub drain and trap. He came back and checked his work and said it was not the cause of the seepage. I believe him because you still can see all of his work thru the removed ceiling blocks, and it isn't leaking.

The leak -- only occurs when using the shower. I tried caulking/grout and using silicone sealant but the leak is still there. The leak shows itself (on the beams below it) as being roughly below the cold water knob. Today I noticed the best clue yet but I don't know how to proceed. Here is what I noticed. I have no idea how to explain it. Turn on the cold water only (filling the tub) and there is a slight dripping from the HOT water knob (the drip is cold water). But when I leave the cold water on and turn on the shower here's what happens .... the drip from the HOT water knob gets noticeably faster and there is a slow drip from the cold water knob too. Note the hot water was never turned on, just the cold.

Any ideas are appreciated. I guess I could call the plumber again, but I was hoping to be able to fix this myself. I'm tired of looking at the missing tiles in the kitchen but I can't fix them till the leak is fixed.

Francis

[LLigetfa]

The stem seals are bad. With the valves closed, there is no water pressure against the seals. With either valve open, because of the crossover blending, pressure exhibits at the seals. If the shower diverter is pulled, there is additional pressure against the stem seals because of the weight of the water up to the shower.

[Terry]

The two handle valve stems may have leaking stems.
Pull the handles off, and the trim that surrounds the stems and see if that's the case.
You can either repair the leaking stems, or pull them, take them to a hardware store and get replacements.
At the same time, you can replace the valve seats.

[fsrph]

Thanks for the advice. That explains a lot. But, can leaking stems/seats cause the leak I am experiencing. The leak seems to begin behind the cold water knob. Looking behind the shower, thru the access panel, I don't see any water dripping nor is the area wet. All I see is the plumbing to the knobs and the drain. The wall looks like plaster with wire in it. I think the leak is on the other side of the plaster and makes it's way to the beams below. Thanks for your advice.

Francis

[Terry]

Then one more place to look, is the galvanized pipe between the brass valve and the shower head.

When galvanized pipe comes in contact with brass, the galvanized pipe loses.
Sooner or later, they all fail at that point.