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How to Install a Thermostatic Mixing Valve

Updated July 20, 2017

The water temperature in a hot water heater needs be kept at approximately 60 degrees Celsius to limit the potential of the unit becoming a breeding ground for Legionella, the bacteria that cause Legionnaire's disease. However, water can cause scalding at approximately 48.9 degrees Celsius, creating a difficult dilemma for homeowners. To address this issue, many areas now require the installation of thermostatic mixing valves by code in residential applications, with exceptions such as a direct line to a dishwasher. Thermostatic valves attach to both the cold water line and the hot water line to alter the cold water to hot water ratio, which allows the temperature of water from the tap to be safe.

Check local building codes to ensure all laws are followed with regard to what qualifications are required by code when installing the mixing valve.

Turn off the main water supply and open all faucets to allow water in the lines to drain. Be patient as this may take some time.

Select a location that will be accessible for cleaning, adjustment and servicing. Also note that dishwashers may benefit from hotter water. Run a separate line directly from the water heater to the dishwasher or to other appliances that might require higher temperature water to avoid using the mixing valve in these cases.

Solder the connections to the thermostatic valve before attaching it to prevent damaging the gaskets. Ensure that the solder is safe for potable water to prevent harmful elements from having contact with water used for drinking.

Tighten the connections to the valve using a wrench.

Turn the water on and check the temperature of the water from a faucet using a thermometer. Allow some time for the hot water to reach the faucet before recording the temperature.

Turn the hand wheel to adjust the dial to the desired temperature. The instructions that come with the thermostatic valve should indicate what the current assumed water temperature is without the mixing valve attached and what difference a one-degree turn will equal in per cent.

Things You'll Need

  • Wrench
  • Screwdriver
  • Solder
  • Torch
  • Thermometer
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About the Author

Eric Jonas has been writing in small-business advertising and local community newsletters since 1998. Prior to his writing career, he became a licensed level II gas technician and continues to work in the field, also authoring educational newsletters for others in the business. Jonas is currently a graduate student with a Bachelor of Arts in English and rhetoric from McMaster University.