First the Faucet that controls a tub shower wouldn't turn on. After some struggle I was able to free it, but then I couldn't shut it off. So I shut off the shut off valves behind the wall. Then when I removed the faucet guts, the water started runnig again leaving me to conclude that the hot water shut off valve would not shut off though the cold water does. So is it possible to disassemble the shut off valve and replace a part inside, like a washer, or will the entire shut off valve have to be replaced?