My home was built in the 70's. My guest bath has a shower tub combination. There is a hot water handle, cold water handle and you pull up a diverter on the spout to the tub to send the water to the shower. When I turn on the hot water (knob on the left) water comes out of the spout and water shoots out from the knob as well. If I close the knob and turn on the cold water (knob on the right) water comes out of the knob on the left as well as the spout. Do I have a serious problem? The plumber that replaced my water heater said they would have to come in from the wall in the hall (behind the tub) and replace everything. I am concerned as water could be going into the wall as well as out the knob, and the grand kids are coming soon and they need to take baths. We have very hard water (lots of calcium) in Arizona so not sure I can do this myself if I need to take the stem and valve out. Thanks

Replacing everything can get expensive plus the wall repair. Try shutting off the main, remove the knob. There should be a hex collar that can be unscrewed allowing you to pull the stem. Replace the seat and the washer since they are in your hand but inspect the stem fro an "O" ring or packing that can be replaced. Make sure you tighten the hex collar when done. This should fix your issue but if you run into the unexpected just come back her.

OK But my fear is this. The chrome sleeve is so calcified that I can not get it to turn. Do both sleeve and the stem loosen counter clockwise? Or is one treaded the other way? I may take the sleeve of with the stem still stuck to it.

Through CLR on it or some vinegar. Don't try acid or drain cleaner. I don't know exactly what your collar looks like but most everything unscrews counterclockwise. Don't forget to shut off your main and open the faucet to insure your watre is completely off.