I have an old shower in my tub/shower set up. The middle control that turns to direct the water to either the shower or tub has stopped working. Usually the middle control has to be turned a half turn to direct the water to either head. Now, the middle control knob turns and turns, as many times as you want to turn it,in either direction. The water is running out the tub and I cannot get the water to come out of the shower head. I tried to make sure the handle was on properly, and the screw that holds the handle is doing the job. I tried to get the housing off around the inner control and I could not get it off.
I am not sure what I need to do to check on this before I call a plumber. I am mechanically inclined but I do not have a vision or directions of what to do. I hope you can help me and tell me the steps I should take to check this out and find out how to solve this problem.