Lot’s of people have a shower that has a single lever to manage the mixture of cold and hot water. The Problem: Shower only got warm even though the water in the sink was hot. Solution: Replace the faucet cartridge
Turn off water to shower or house.
Turn off hot water if heater is on same floor as shower. Isolate Hot Water Heater.
Tools: Phillips and flat screw driver, maybe a strap wrench.
Cover drain hole in shower base (prevent lost parts)
Remove cap on shower control handle. Might need flat screw driver to pry off..
Next remove Phillips screw in center of faucet. If your shower faucet had independent heat selector – Remove now.
Remove outer chrome sleeve
Unscrew the collar nut, should be finger tight.
Cartridge should be extracted easily.
Don’t loose little rubber plugs that may pop out after cartridge is removed.
Take cartridge to local hardware or plumbing supply store and get a new one to match.
Reinstall cartridge using reverse steps
turn on water, check shower for leaks and heat
Last step? Do your happy dance because you just fixed that darn shower!