Re: upstairs shower
You may have a faulty shower valve.
If it's a single-handle shower, simply replace the cartridge. If after installing the new cartridge hot and cold are reversed, carefully remove the cartridge, rotate it 180 degrees, and reinstall it.
If it's a 2- or 3-handle shower*, check that the washers on the inside of the stem are not loose. If they are worn, replace them. If the handles are chrome, you may need a special puller to get them off since they are probably corroded on. Then you'll need a crescent wrench to remove the stem.
(*Some 2- and 3-handle showers use cartridges instead of compression washers on stems.)
Be sure to shut off the water first.
Never use a pipe wrench or channel-lock type pliers where a crescent wrench will do. Toothed jaws will absolutely ruin a smooth finish, every time.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.