Our shower no longer has any hot water pressure. We have cold water and when we turn the cold water on, it completely takes over and its like we have no hot water at all. We have changed the washer a few times. The faucets are at least 20 years old. There is a hot and cold faucet, a component to turn the shower on and its own spout. We have changed the shower head to a hand held because oh my disability. When you turn the hot water faucet on, the faucet seems to come out approx. a half inch.

Does your faucet have two handles that turn the water on and one handle that makes the water switch from the tub faucet up to the shower head?
You mentioned that the hot side of the faucet only comes out 1/2 inch, what do you mean by that? If that is what it does it is possible that you need to disassemble the faucet and clean it, maybe put some heat proof grease on the threads of whatever operates in the faucet.

No there are 2 separate faucets and another to turn the shower on by turning it. We have taken the hot water faucet off, replaced the o-rings, cleaned it, used a compressor to blow the lines out in case debris was blocking it, turned the water back on with the faucet on to get rid of debris by water pressure, we do have good pressure with the faucet off. We got a bit of debris out when we turned the water on. The spout is fixed to the wall and when we tried to turn it, even with a wrench, it just felt like it would break off, so we stopped wrenching on it. Could there be a filter somewhere between the faucet and the spout water line that is filled with debris? We have had problems in the past with scale build up in our copper lines, is there something we can do to stop this? We have a 50ish year old house, hoy water heat in the floors and the hot water heater was changed about 15 years ago.

If you could tell me what kind of faucet you have or maybe take a picture, even with your phone and post it I might be able to tell you more.

Would this look like your faucet? (see image). Tom