Hundreds of people suffer burns, scalds and other injuries each year from overheating tap or shower water. By contrast, the deadly Legionella bacteria can grow in water heaters that are set too low to kill the organism. Thermostatic mixing valves can help with both of these problems. [Image credit: istock.com/DenBoma]

How to Install a Thermostatic Mixing Valve
Time: 1-2 hours
Frequency: as needed
Difficulty: Basic plumbing and welding experience recommended
Tools: adjustable wrench, hex key, screwdriver, solder, thermometer
Thermostatic mixers can be installed on the water heater itself or on a specific plumbing fixture, such as through a shower valve. Here are four key steps to understanding and installing a thermostatic valve in your water heater.

Step 1: Learn about Thermostatic Mixing Valves
Thermostatic mixing valve mixes hot and cold water to ensure constant, safe shower and tap water temperatures to prevent injury. Hot water can cause scalding, but more commonly, injuries are caused by “thermal shock,” such as slipping or falling when the water coming out of the shower head is hotter than expected.

The thermostatic valve contains a mixing chamber that regulates the inflow of hot and cold water to a preset temperature. The maximum temperature can be adjusted depending on the brand and type of mixing valve installed, but a temperature of 60˚C (140˚F) is generally recommended in Canada to kill deadly bacteria associated with Legionnaires’ disease.

careful!
Always check the maximum outlet temperature recommended by the brand of thermostatic valve installed. When in doubt, consult a professional plumber.

Step 2: Prepare to install the mixing valve
While professional installation is the best way to ensure the job is done safely and accurately, these steps describe the basic process of installing a mixing valve in a supply tank. Shower valves can also be used, for example, when they require a different temperature setting than other faucets or appliances.

Before starting the installation, make sure you are ready for the job:

Turn off the main water supply.
Turn on all the faucets in the house and let the pipes bleed. This will empty the remaining water in the pipes.
Choose a mounting location for the mixing valve that is easy to clean, maintain, or adjust.
Good to know!
It will take a while to drain the water lines, so please be patient! Also, some appliances, like dishwashers, can benefit from extra hot water. Consider connecting directly from the water heater to the appliance and bypassing the thermostatic valve.
careful!

Always check your local building and plumbing codes for any qualifications or specific procedures required to install a thermostatic mixing valve.

Step 3: Install Thermostatic Mixing Valve
Once you have turned off the water and selected an installation location, you are ready to install the valve.

In general, the mixing valve can be installed in any position, but please refer to the manufacturer’s instructions to ensure this is the case for the model you choose.
Connect the water supply. Each hot and cold supply pipe has a connection location, a mixed water outlet for the heater.
Weld the valve connections before securing the mixing valve in place to prevent damage to any gaskets. Your valve can be threaded to the pipe without welding.
Attach the mixing valve to its position and tighten with a wrench.
After installing the thermostatic valve, turn on the cold water supply, then the hot water supply and check for leaks.
Step 4: Adjust the temperature
You can check the temperature of the hot water by turning on the faucet and using a thermometer. To stabilize the water temperature, let it flow for at least two minutes before checking the temperature.
If you need to adjust the water temperature:

Use a hex wrench to unlock the temperature adjustment screw on the thermostatic mixing valve.
Turn the screw counterclockwise to increase the temperature and clockwise to decrease the temperature.
Tighten the screws and check the temperature again.
Good to know!

For safe use, check the manufacturer’s instructions for the mixing valve’s recommended maximum and minimum heat settings.

Congratulations, you have successfully installed or replaced a thermostatic mixing valve and ensured that your home will have germ-free hot water throughout the house for years to come. Time to relax with a hot bath and reflect on your craft.