I have 3 faucets in my tub/shower. Faucets for Hot and Cold water and the middle faucet for turning on and turning off the shower. This morning when trying to turn off the shower with the handle it became loose in my grip. The handle just turns loosely around and around. I turned of the hot and cold water faucets to stop the shower. I am wondering if the threads in the handle have been stripped? or maybe the stem? Any ideas? How to repair?