Shower valves live in the walls behind shower faucet handles, and they turn the shower on and off and adjust the shower temperature and pressure. One of the most traditional kinds is a mixing valve. It mixes the hot and cold lines to get the proper temperatures. Moen manufactures and sells these kinds of valves, and adjusting the hot and cold water is easy.
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Types of Shower Valves
There are several different kinds of shower valves, and each of them serves a different purpose. The mixing valve is an older style that has two separate valves that you can adjust on their own by twisting them. It draws water from the hot and cold taps to the showerhead, and it may have a central knob (for bathtubs) or a single knob (for showers). Newer-style temperature regulating valves, somewhat predictably, regulate the temperature of the water, and pressure-balancing valves use the alternative method of balancing pressure for the purpose of maintaining temperatures.
Thermostatic valves maintain temperature and pressure and often use internal cartridges. These valves are a high-end choice and allow you to preset water temperatures before you even turn on the water so that you won't have to wait. Finally, diverter and transfer valves control the water flow from one faucet to another faucet or showerhead or to multiple other outlets.
Moen Temperature Adjustment
If your Moen mixing valve is acting up, you can try to adjust shower temperatures yourself. There are plenty of video tutorials that explain how to adjust the setting to make the water hotter. Turn off the water first and use an Allen wrench to remove the setscrew from the bottom of the handle and pull it off. Take a Phillips screwdriver, unscrew the setscrew and remove the black plastic fitting.
Pull out the escutcheon tube and pull off the top part. Look at its white spine; you can adjust the temperature setting here. Move the two parts to meet at the top position if you want access to the water's high-limit temperature. Return the valve parts to the fixture and then the handle. You can now turn the handle to the left and right. Be careful, though, because the water can be scalding if you aren't careful enough.
Moen Mixing Valve Adjustment
To adjust the Moen temperature on a mixing valve, take a flathead screwdriver and pry off the handle's cap. Then, hold the handle still and turn its mounting screw to the left with a Phillips screwdriver. Take it off and put it aside. You'll see a trim ring on the flow valve; take this off, and you'll see the stem and knob. Turn the stem to the left, which will divert the water flow to your showerhead. Give it about three minutes, measure the temperature with a thermometer and turn off the valve.
Remove the knob from the stem. If the water temperature feels too hot or is over 120 degrees Fahrenheit, give the knob a quarter turn to the left to adjust the shower temperatures. Did the water feel too cold? Just turn the knob a quarter turn to the right. Now, you can put the knob back onto the stem and return the trim ring to the flow valve.
Reinstall the shower handle, tighten it and press the cap back into its hole. That's all there is to this quick DIY fix. If the fix didn't work and you need to replace your Moen mixing valve, these can range from $42 to $138 in price.