I have a bathtub upstairs, if I let the water drip everything is fine. If I shut it off real tight then a drip comes through in the roomdownstairs through the ceiling. Is it pressure in the line? Why would it leak when closed? As long as the hot or cold is dripping everything is fine.

You have a leak in a fitting or pipe. When you turn the valves closed, water pressure builds up and it leaks. When the valves are opened, the pressure drops and it doesn't leak. Look for an access panel behind the tub valves or open a hole in the wall behind the valves. You should see where the water is coming from. Hopefully you have access. Otherwise, you will have to rip out the tile wall to repair the leak. It's better to fix the leak because continued dripping can cause mold and structural damage. If the valves are on an outside wall, hopefully not, you may have had a frozen pipe that developed a small crack.

Hi Robinsol...

Start by removing the handle and the trim plate from the front of the shower and then use a flashlight to see what you can determine.

The issue could be at the handle/stem packing nut.

The issue could be at the diverter spindle (if integral to the valve body).

The issue could even be from up at the shower arm of the shower head... would show up as dripping onto the valve from above (when viewed from inside the wall). If nothing is revealed from this approach then go around back ad disconnect the access panel (if present) and see what you can determine from there... could be shutoffs as Brian suggested, for sure.

Otherwise, you may need to cut an access panel on your own.

Let us know what you discover as you go, OK?

Mark