Hot water knob HARD TO TURN

Just moved in w/my friend. She don't use hot water to bath because when she turns the knob, it only turns about an inch. Trickle of water comes out, but only for a couple of seconds. ALL the hot & cold water in the house works, except for this hot shower knob. We don't know the brand name. What could be the problem? She used to have hot water, but little by little, she said it started taking a while for the hot water to come out. Eventually, she rarely used it. Now you could barely turn it, nor much hot water come out.

If you could post a pic of the shower valve, we could probably tell you what it is.

In general, your cartridge is stuck and you may also have stuck balancing spool. These parts are generally easy to replace. You do have to bet exactly the right parts.

valve

The stem's threads have probably gotten mineral accumulations because of disuse. Remove the stem, take it to a hardware store, have them identify it, and then install the new stem.