Have problem with the bathtub hot water, The cold water comes out of all the faucets in the house OK,
The hot water comes out of all the faucets OK also but the bathtub. It comes out in a crawl. Really slow almost none. But the cold comes you great.

What is the problem? Is it the pipe the that part of the house or the faucet unit?

:( :(

It is most likely the valve or cartridge on the hot side of your faucet. Shut off the main, remove the hasndle and the bezel. You should see where a wrench can unscrew the valve/cartridge. Clean it, flush it ir replace it. You should be good to go.