Every hot water faucet in my house produces scalding hot water. EXCEPT the upstairs tub/shower. From that faucet we only get lukewarm water. Why? What should be replaced?

bradsmithmm

Hard to say w/out knowing which shower valve you have and how old it is.

Look for a high limit device under the handle that limits the distance the handle can turn. Do not remove this, it is there for your protection. Simply adjust it to suit you.