Causes: Worn out valves, seats and gaskets are common culprits. "Turning faucets on and off over the years wears these parts out," Hogan says. A faucet valve cartridge can also be to blame.

You should have some experience working with plumbing (P-traps and/or faucets) and basic carpentry tools. If you replace the shower valve and have copper supply lines, you'll need soldering skills.