Plumbing – How to fix a bathtub faucet that leaks only when the shower runs

bathroombathtubplumbingshower

I just moved into an apartment and the faucet in the tub is fine when all of the water is off. It leaks when I turn on the water and switch it to the shower head. What could be the problem?
It's a rental so I don't want to take the switching mechanism off to investigate. I suspect it's some sort of rubber seal in the switch.

UPDATE

The control is a twist knob between the cold and hot twist knobs.

Best Answer

Sounds like the washers/gaskets on the valve have gone bad, you'll have to either replace the washer or the entire valve (if you can find a replacement).

Here is what the valve may have looked like when it was new (just to give you an idea of what you're dealing with).

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Removal

  • Turn off the water to the shower faucet using either a local shutoff valve or the main water valve for the house.

  • Turn the shower’s hot and cold water all the way on, to drain leftover water from the pipes.

  • Pry the cap out of the center of the diverter’s handle.

  • Remove the screw in the middle of the handle, and then pull the handle off the faucet.

  • Unscrew the metal sleeve that sits over the valve stem.

  • Insert a Shower Valve Socket Wrench over the valve stem and turn the dirervter anti-clockwise to remove it.

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Installation

Installation is the reverse of removal.

  • Insert a Shower Valve Socket Wrench over the valve stem and turn the dirervter clockwise to install it.
  • Screw on the metal sleeve that sits over the valve stem.
  • Push the handle on the faucet, then replace the screw in the middle of the handle.
  • Push the cap into of the center of the diverter’s handle.
  • Turn the shower’s hot and cold water all the way off.
  • Turn on the water to the shower faucet using either a local shutoff valve or the main water valve for the house.
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