I find showers and baths to be most relaxing when the water is maintained at an appropriate temperature, which is what a mixing valve accomplishes when installed, and it's important for new installations. The other thing I recommend installing with any type of mixed-ventilation plumbing installation such as my own was anti-scalding valves; these protect you from burns that result from hot water mixing with colder water that is cooling down too fast!
Here are the steps for how to install a mixing valve on a water heater. Keep in mind, if you’re not handy or are unsure about any of these steps, it may be best to contact a professional.
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Getting Ready
Ensure the water heater control knob was turned to the, “pilot” position. Turn off the shutoff valve at the cold water line, which attaches at the top of the tank. Next up, turn on a hot and cold faucet inside the house and allow excess water in the pipes to drain out. Now step away from the heater for a few hours and let both the tank and vent pipe cool down. You’ll know it’s ready when it’s cool to the touch.
To detach your heating vent pipe from the top of your heater, first lift up on the flange at its base. Then push it and the lower end back towards you to break their connection.
Using an adjustable wrench, it's possible to loosen the fitting at the upper end of a cold water line. Detach the fittings from one another and move them apart (in opposite directions) before reversing their original alignment with each other - this will create enough room to safely insert your fingers between the lines without any struggle.
Cold Water Connections
Wrap vinyl plumber's tape over the threads underneath your shutoff valve where you detached the flex-line.
Screw on a galvanized male and female coupler fitting to attach it back in place with a screwdriver.
Fit one end of an adjustable pipe wrench onto your cold water line, which attaches at the top of this new connection; furthermore, double-check for loose parts, which will help prevent future leaks due to faulty connections or ruptures elsewhere in these pipes nearby!
Tighten up all fittings by hand so they're secure and nothing leaks from either direction when turning both handles together left/right (clockwise).
You will need to hold the mixing valve with the knob pointing up and align the cold-water Tee at end of shutoff valve. Pull off the blue cap from the point it connects to your pipeline before wrapping tape around threads. Hold the valve with one hand and screw the inlet onto the male end of the coupler. Tighten the mixing valve two rotations clockwise with the adjustable wrench.
Wrap vinyl tape on the threads at the underside of your cold-water tee, and then screw it into place by hand. Hold onto your mixing valve with one arm while you tighten its fitting with an adjustable wrench.
Hot Water Connections
Loosen and detach the fitting at the upper end of a hot-water flex line from the pipe that runs to your house with an adjustable wrench. Once that step is complete, move it aside so you can continue.
Wrap vinyl tape on the threads of your hot-water pipe and fit a water heater flex line to it. As an alternative, wrap the end with a pipe wrench as back up.
In order to make this process easier, remove the red cap from the bottom of your mixing valve.
Next, wrap vinyl tape around the threads and attach the 12 inch flex line to the underside using an adjustable wrench.
Pull off the red plastic cap from the lower end of the hot-water tee on the valve. Wrap vinyl tape on the threads. Attach the upper end of the original flex line that was detached from the hot-water pipe to the hot-water tee, using the adjustable wrench.
Open the shutoff valve at the cold-water pipe slowly. Now check for drips at all connections ensuring that there are no leaks. If necessary, tighten a connection to stop drips.
Secure the vent pipe back in place. Turn the water heater control to mid-range temperature and allow water in tank to heat for about an hour. Check the installation instructions before adjusting the temperature on the mixing valve and water heater.
Enjoy the Warm Water
A quick recap of the steps for installing a mixing on a hot water heater: First, turn off the power to the water heater. Next, remove any insulation around your old valve and unscrew it from the top of your tank. Once you've done this, slide out your old stem assembly if necessary and discard or recycle it properly. Keep your workplace organized to avoid the loss of parts!
Now install new stems by placing them in their proper order inside the hole at the bottom of your tank so that they are standing up vertically (stem A goes on top). Screw them into place with some Teflon tape using an adjustable wrench until tight enough that you can't get more than 1/4" between each part when pressing together. Finally, screw in all three valves snugly, and enjoy the warm water!