Things You'll Need
A Moen shower valve contains a mixing valve that sets the water's high-temperature limit. A home's hot and cold water pipes feed a Moen shower valve. The shower valve's mixing valve, sometimes called the temperature valve, combines the hot and cold water and diverts the resulting mixture toward the shower head. The mixing valve's control knob limits the amount of hot water flowing through the valve. Adjusting the mixing valve's control knob changes the ratio of hot-to-cold water exiting the Moen shower valve.
Pry the cap off the Moen shower valve's handle, using a slotted screwdriver for leverage. The cap slips into a slot on the end of the shower valve handle and covers the handle's mounting screw.
Hold the shower valve handle still with one hand and turn the handle's mounting screw counterclockwise with a Phillips screwdriver. Pull the handle off the shower valve's flow valve. The handle slips over the end of the flow valve's stem.
Slide the trim ring off the flow valve, exposing the flow valve's stem and the mixing valve's knob.
Turn the flow valve's stem counterclockwise, turning on the water flow through the shower head. Wait for the water coming out of the shower head to reach its maximum temperature, usually about two to three minutes. Measure the water temperature with a thermometer. Turn the flow valve's stem clockwise, turning off the water flow.
Pull the mixing valve's knob, the plastic knob surrounding the flow valve's base, off the flow valve's stem. If the thermometer's reading exceeded 120 degrees Fahrenheit or the water temperature feels too hot, turn the mixing valve's knob counterclockwise one-quarter turn. Turning the knob counterclockwise lowers the water's high-limit temperature. Turn the mixing valve's knob clockwise a quarter-turn to raise the water's high-limit temperature. Slide the valve knob onto the flow valve's stem.
Slip the Moen flow valve's trim ring onto the flow valve. Slide the shower handle onto the end of the flow valve stem and tighten the handle's mounting screw with the Phillips screwdriver. Press the cap into its hole in the end of the Moen shower valve handle.