Have you ever been standing in the shower, only to get blasted with super hot (or super cold) water when someone elsewhere in the house flushes the toilet or runs the water? Installing an anti-scald valve in the shower will put an end to these jarring and dangerous surprises.
Anti-scald valves, also known as pressure-balance valves, compensate for sudden pressure changes in both hot and cold water lines. This prevents the temperature from changing in response to other water draws. Since sudden temperature changes can cause a showering person to jump or otherwise lose his or her balance, keeping the temperature even can prevent slips and falls. It can also prevent scalding injuries — hence the name, "anti-scald valve."
Turn Off the Water and Take Measurements
To install an anti-scald valve, the first step is to turn off the water supply to the shower you'll be working on.
Then remove the current handle and escutcheon plate (that metal plate that goes behind some water handles in the shower). Measure the setback from the outside of the tile to the center of the pipes in the wall. This is one time you don't want to buy the new part first. That's because you need an anti-scald valve that has a similar setback for easier installation.
Remove the Old Plumbing
The next step in installing your new anti-scald valve is to get behind the valve, from the other side of the wall. If there isn't already an access hole, you'll need to cut one in. Once you have access, remove the tub spout and shower arm. Cut the supply lines where the shutoff valves will be located. Remove the old faucet valve and old piping above where you made the cut.
Use the old valve and pipes as a template for determining the size of the new anti-scald valve assembly. Solder connections, using a fireproof cloth to keep from lighting the work area on fire. While soldering, open the shutoff valves and remove the valve cartridge. Secure the valve and pipes with support blocks and pipe straps.
Install the New Plumbing and Test the Anti-Scald Valve
Go back to the shower side (front). Now install the new escutcheon plate, set the anti-scald limiter, and install the new handle. Install the tub spout and the shower arm. Test the anti-scald valve and the connections.
To adjust the anti-scald valve, look for a gear-like rotational stop behind the handle. This stop controls how hot the water can be turned. All you have to do to get at this part is remove the handle — no need to cut back into the wall. This makes it fairly easy to re-adjust if you find you aren't satisfied with the way it's initially set up.
Once these steps are complete, you have finished installing the anti-scald valve. You can now enjoy taking a shower, knowing that you won't be blasted in extremely hot or cold water whenever someone runs water elsewhere in the house.