Moen tub and shower faucets use a Posi-Temp feature to reduce the chance of scalding due to extreme hot water temperatures. As the seasons change, it becomes necessary to make adjustments to the water temperature. Adjust the temperature on a Moen shower requires some disassembly of the faucet handle. The temperature is controlled with a limit stop that prevents full opening of hot water. This stop is what you adjust to change the water temperature.
Turn the Moen faucet handle to the full hot position and allow the cold water to purge from the line. Hold a thermometer under the running water, once the water is running hot. The temperature should be no more than 120 degrees Fahrenheit.
Shut off the water at the faucet and shut off the two water supply valves to the faucet. The supply valves are behind the shower fixture wall. Open the shower faucet once more to drain any residual water and place the faucet in the off position.
Remove the handle from the faucet. The Moen shower handle installs in different ways, depending upon the style. Some have a set screw underneath the handle that you can remove with an Allen wrench, and others have the screw hidden behind a decorative cap. The screw behind the decorative cap usually requires a Phillips-head screwdriver to remove. Pull the handle away from the wall.
Loosen and remove the screw securing the cartridge key stop to the top of the cartridge with a Phillips-head screwdriver. Pull the key stop away from the cartridge.
Pull the limit stop ring away and out of the cartridge sleeve just enough that the ring teeth disengage from the sleeve. Turn the ring clockwise to increase temperature, or counterclockwise to decrease temperature. You only need to rotate in small increments. Insert the ring back into the sleeve.
Install the cartridge key stop and secure with the retaining screw. Install the handle and secure it to the faucet with the retaining screw. Turn on the water supply and check the hot water temperature again. Continue making adjustments to the temperature as necessary.