I have a new washing machine. The hot water hose CONNECTION to the hot water faucet and shut off connection is corroded and I am unable to unscrew the hose connection to the hot water faucet/shut off valve. Will I have to replace the whole box containing both hot & cold water faucets and replace? Which would involve removing dry wall and new box with hot & cold connections. Is is possible or feasible to remove the corroded connection with hose? From the faucet threads. Thanks.

It can require a lot of work, as you note. However, I would first soak the faucet end / fitting with WD40 or similar, wait a while, heat the fitting with a hair dryer and try to unscrew. Another possible solution, IF the hose is in good shape, would be to use the old HW hose and connect it to the washer stub out.

You should be able to remove the hose, even when the metal end is corroded. Grab it with large channel locks and turn hard.

The hose metal threaded connection is softer metal then threaded end of the valve. You could even break it off without damaging the valve threads. Be patient with it.

Once the hose is removed, take wire brush and brush off all rust. I would put lubricant on the threads on the valve to prevent ( or delay ) the process of corrossion

It is a good habit to deal with corroded connections as they are discovered. Don't let it go too far. Fix it, repair it, or replace it right away

Hope that helps

Milo