Single-lever faucets in showers, tubs and sinks operate by mixing the cold and hot water together to achieve a temperature. Turning the lever 45 degrees to the right allows cold water flow only. At 135-degrees rotation the hot water starts mixing with the cold. At the full turn of the lever at 270 degrees only hot water is flowing. If the water temperature never gets hot enough at the full open mark, you can make adjustments inside the faucet to increase the temperature. Consequently, adjustments are available to add more cold water to the mix also.
Newer-Style Single-Lever Faucets
Remove the lever from the faucet. Some models of single-lever faucets have a plastic or metal on the front of the lever. Pry this off with a small flat screwdriver to remove the lever. Other models have a small screw underneath the faucet. Insert a small Phillips screwdriver and turn counterclockwise to remove the screw.
Locate the one or two-piece plastic collar inside the faucet with a small plastic protruding nub. The one-piece collar has the nub on it and the two-piece collar has a separate plastic protruding nub. Push the nub clockwise to obtain a cooler maximum water temperature from the faucet. Push the nub counterclockwise to obtain a warmer maximum water temperature.
Place the lever back on the faucet and test the water to provide the adjustment necessary for hotter or colder maximum water temperature. Make nub adjustments in small increments and let the water warm up for a minute or two to test the adjustments.
Older-Style Single-Lever Faucets
Remove the faucet lever in the same manner as a newer-style single-lever faucet. Set the lever aside.
Locate the two adjustments screws in the faucet. The screw on the left side is the hot water adjustment screw and the right-side screw is the cold water adjustment screw. To increase hot water turn the left screw counterclockwise with a Phillips screwdriver for more hot water flow. The cold water may also adjust by turning the screw clockwise to add more hot water by decreasing the cold water.
Adjust the temperature to a cooler setting by turning the left hot water screw clockwise or turning the cold water right screw counterclockwise. Make small incremental adjustments, replace the lever and test the temperature.