Shower mixing valves are installed behind the wall to balance the water temperature on the house's main water valve. This keeps you from getting scalded in the shower when someone runs another faucet in the house. Two common problems with shower mixer valves include leaks and water that is too hot or cold.
However, these valves are permanently attached to plumbing and you need to access the valve through a panel for repairs. Here are some tips on fixing a shower mixing valve.
Gain Access to the Valve
Shut off the main water supply to the house and open the faucet to relieve water pressure. Cover the drain so you won't lose any parts. Remove the shower faucet handle and the escutcheon plate with a screwdriver. Look for an access panel around the shower wall, in a nearby closet, or basement. If you can't find an access panel, cut an 18 inch by 18 inch hole in the wall at the rear of the shower using a drywall knife starting from the center at the facet height.
Adjust the Screw on the Valve Stem
If the water is too hot too cold, the screw on the valve stem needs adjusting. Look for a screw on the valve stem and rotate it right a time or two. Run the water with full pressure to check the temperature and reattach everything once you get the right temperature. Some shower mixer valves have preset temperatures for safety reasons, but the temperature can be raised by pressing the safety button on the mixer valve handle.
Replace the Washers
Sometimes, the cause of leaks are bad washers. The knob or handle on the valve has to be removed to expose the two washers. Look for a screw on the end of the knob or one hidden by a cover. Pry off the cover with a Phillips screwdriver and take off the screw to expose the washer.
Remove the washer with needle-nose pliers or tweezers and find a replacement. Take off the valve at the cylindrical tip with your pliers turning gently. Remove the valve from the socket to access the second washer and remove it with pliers or tweezers.
Insert the new washer pushing it in place with the tweezers or pliers. Set the valve down in the socket and insert the second washer. Reinsert all covers and test the shower.
These tips should help you fix the two main problems with shower mixer valves. If your repairs fail or you have a tiled wall, you will need the services of a plumber to find the cause of the problem.