How to Adjust a Thermostatic Mixing Valve in a Bathtub

A thermostatic mixing valve in a bathtub fixture allows you to limit the flow of hot water through the plumbing to prevent injury. Depending on your faucet brand, this safety feature may also be referred to as an anti-scald setting or rotational limit stop. The thermostatic adjustment control is underneath the knob or handle on the bathtub fixture. Adjusting the setting takes only a few minutes using basic tools.

Thermometer
Screwdriver or Allen wrench
Needle-nose pliers

Instructions

- 1
  Turn the knob on the valve for the hot water into the bathtub to the maximum setting, and wait until the water flows as hot as possible.
- 2
  Hold the thermometer into the flowing water to take a reading. If the water temperature is higher than 120 degrees Fahrenheit, it has the potential to produce scalding injuries, especially to children and elderly individuals using the bathtub. Turn off the water.
- 3
  Take out a slotted or Phillips-head screw in the faucet handle using the appropriate screwdriver. If your model has a hollow set screw in the side of the handle, use an Allen wrench to loosen it. Pull off the knob or handle.
- 4
  Grip the metal cover plate with needle-nose pliers, and pull it forward to the unlocked position. The thermostatic adjustment wheel is behind the cover plate and has a row of gear teeth around the perimeter.
- 5
  Pull the thermostatic wheel outward and adjust it counterclockwise to lower the maximum water temperature the mixing valve can produce. Each adjustment by one gear tooth lowers the temperature 4 to 16 degrees Fahrenheit.
- 6
  Push the adjustment wheel back into the valve stem. Press the metal cover plate to lock the new temperature setting.
- 7
  Slide on the handle or knob, and secure it with the screwdriver or Allen wrench, depending on the hardware for your faucet.

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