What is the problem when my bathroom ceiling leaks only when the shower is on? It does not leak if the tub water runs.

It is possible that you have a joint that has gone bad and is spraying water above you if your in a single story situation. Your pipes should come from under the floor. But the pipe to the spray nozzle goes up higher.

You may have to open the wall somewhere to find out.

If you have a shower head on a hose, hang it down in tub and turn it on. If you get a leak in ceiling then there is a break in pipe feeding shower.

If not then there is a leak in the caulking and/or grout for the ceramic tile.

If a break in pipe you will have to open wall to repair.

If not check corners to see if grout is cracked. Also check where tub and wall come together. Clean out old grout and redo with tub seal.

Chuck

Purchase a 1/2" PVC pipe cap. Remove shower head, screw on pipe cap. Turn on shower. If you get water in the ceiling below you have a leaking joint where the shower arm screw into the drop ell.

To correct, unscrew shower arm, coat threads with generous amount of pipe thread sealer. To avoid scaring up the shower arm use either a strap wrench or stick a long screwdriver up the shower arm. While holding the shower arm at the wall with one hand, rotate the screwdriver in a circular fashion. A 10" extension from a 3/8 drive socket set works great.