I just purchased an older home(late 70's) and the shower isn't working correctly. I have a 3 handle shower(hot, cold, and faucet that turns on shower). When I turn the center knob so the water will come out of the shower head the water will still come out of faucet below as well as the shower head. The pressure coming out of head is still very strong. I am not sure what to do. Can anyone give me any suggestions??PLEASE HELP