How to Adjust an Anti Scald Valve (Thermostatic Mixing Valve)?

Have you ever been in a shower when you were suddenly hit with hot, scalding water just because someone else ran a tap or flushed a toilet in the house? Didn’t you just hate it?

How to adjust an anti scald valve - Adjusting anti scald valves correctly can avoid temperature fluctuations

If you have ever been in this uncomfortable situation, an anti-scald valve (thermostatic mixing valve) can solve this problem for you! Anti-scald valves maintain the temperature of water in a shower, bathtub, or faucet at a set level at all times and stop water temperature fluctuations.

Over the long term, an anti-scald valve will save you money, by reducing the flow of hot water. It will also save you time which you will spend adjusting the valve.

Check out the top-selling anti-scald valves from Amazon below.

Bestseller No. 1
KES Pressure Balance Shower...
310 Reviews
KES Pressure Balance Shower...
  • BRASS VALVE: Faucet body is made from high quality brass, ensuring quality and longevity.
  • cUPC CERTIFIED & ANTI-SCALD: advanced pressure balance ceramic disc cartridge with cUPC certification can effectively protect you from scalding injury caused by sudden changes in hot or cold water pressure, maintaining consistent water temperature.
  • TEMPERATURE LIMIT STOP: If inlet water temperature changes seasonally, please following included instructions to readjust the temperature limit stop. Recommended water temperature for bath or shower is between 90°F - 110°F.
  • CONNECTION SIZE: 1/2'' NPT. Recommended installation height from floor: 100-150 cm.
  • TRIM AND HANDLE INCLUDED: KES shower faucet kit includes rough-in valve, faceplate, and faucet lever. Faceplate and handle are in industry-leading polished chrome finish (mirror-like), build to resist daily scratches and corrosions.
Bestseller No. 2
Atmama Three-way Thermostatic...
117 Reviews
Atmama Three-way Thermostatic...
  • US STANDARD FITTINGS -Coming with 3 PCS G1/2 British straight thread to 1/2NPT adapters
  • MARKINGS in FAHRENHEIT-different from others , Temp settings on this water mixer are in Fahrenheit
  • CONSTANT WATER TEMPERATURE - These Thermostatic Mixing valves are the safety feature preventing scalding water
  • LEAK-FREE CONSTRUCITON-one-piece STURDY BRASS body ensures no leaking
  • TIPS: the temperature markings have very little bearing on reality. So this must be calibrated if you're looking for an accurate temperature
Bestseller No. 3
SharkBite 24549 Thermostatic...
11 Reviews
SharkBite 24549 Thermostatic...
  • COMFORT: Thermostatic mixing valve increases usable hot water on existing water heaters and new NAECA compliant water heaters
  • PROTECTION: Controls hot water to prevent injury from scalding when showering, bathing or washing by ensuring water is delivered at a safe temperature to all fixtures
  • SAFETY: Reduces the risk of Legionella bacteria growth by enabling hot water to be stored at a germ killing 140 degrees Fahrenheit (60 degrees C), while ensuring that water is delivered at a safe temperature to outlets
  • COST EFFECTIVE: Adding a Thermostatic Mixing Valve to an existing water heater allows water to be stored at a higher temperature
  • ASSEMBLED AND TESTED: Prepared in Cash Acme manufacturing plant in Cullman, Alabama

Last update 2021-08-04 / Affiliate links / Images from Amazon Product Advertising API

Below we discuss what anti-scald valves are, how they are useful, and how to adjust them.

Why are anti-scald valves or thermostatic mixing valves needed?

Temperature fluctuations can be caused due to changes in pressure in either the cold or hot line. For example, when someone flushes a toilet, cold water flows to the toilet and reduces the pressure in that line. Therefore, less cold water is available in the pipes.

Anyone bathing at that moment may feel a sudden increase in water temperature. This situation can be further worsened if the plumbing is either narrow or clogged, or there are several showerheads installed.

This kind of inadvertent temperature increase can lead to scalding. Even worse it might cause the person who is taking a bath to get startled and lose balance, leading to other injuries such as fall injury. This puts elderly people and children at high risk since they are more susceptible to shock.

An anti-scald valve or a thermostatic mixing valve is the perfect solution for this kind of problem. The video below tells you more about a thermostatic mixing valve and how it works.

All about Thermostatic Mixing Valves

While having the water too hot can cause scalding, it is a lesser-known fact that the water temperature being too low is also a cause for concern.

Most home water heaters default to 140°F unless any changes have been made to them. At this temperature, it takes about 5 seconds for a severe burn to happen.

Instead, if we start using water at the standard recommended temperature (120°F), we may be encouraging bacterial growth. Bacteria can thrive at temperatures below 140º F, especially in moist places such as water heaters.

How to adjust an anti scald valve - Anti scald valves ensure water temperature will not suddenly change
Anti scald valves ensure water temperature will not suddenly change in faucets or showers

The elderly and children, who have a weaker immune system are susceptible to the bacteria Legionella which thrives at lowered temperatures. These bacteria are the root cause of Legionnaire disease, which is a severe form of Pneumonia. (source)

The Legionnaire disease is known to spread primarily through water droplets. Factors such as water temperature and the mineral content of the water impact its growth.

Therefore, it is important to keep the water in the heater at a higher temperature (140°F+), while using a lower temperature at the point of bathing or washing (110° – 120°). This is where anti-scald valves come into the picture.

Anti-scald valves protect against both these dangers by maintaining water temperature at a safe level, despite fluctuations in the supply line. They are equipped with a mechanism that balances the cold and hot water inputs, keeping the temperature within a safe range.

A woman showering

Anti-scald valves or thermostatic mixing valves also increase the availability of hot water. They draw hot water more slowly from the pipes.

These valves ensure automatic water supply is cut off in case of a failure on either the cold or hot water supply side. This minimizes the possibility of an accident due to a sudden disruption in the pipeline supply.


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How do anti-scald valves work?

Pressure Balanced Valves

A pressure balanced valve is an inexpensive, simple design for an anti-scald valve. Essentially, a piston or a diaphragm is put inside the faucet, and it regulates water flow based on pressure changes.

If the warm water pressure drops, the piston limits the amount of cold-water flow, and vice versa. If the heater temperature is changed, this kind of anti-scald valve must have its heating settings changed along with it.

Thermostatic Mixing Valves

Thermostatic mixing valves have the distinct advantage of not having to be calibrated after being installed once. They operate by mixing the cold and hot water in a small chamber before letting it pass through the faucet.

The chamber contains a thermostatic element that expands and contracts basis the temperature change. Increased temperature expands the element, blocking the warm water, and if the temperature reduces, the element contracts, letting in more hot water.

Types of Anti-scald Valves

There are two basic types of anti-scald valves:

  • Screw-on valves that reduce hot water. These are DIY and easy to install.
  • Valves that adjust the water temperature in the pipe itself. You can install them yourself if you are handy, or you can hire a plumber to install it.


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How to install your anti-scald valve?

Installing an anti-scald valve can be a fairly lengthy exercise that involves plumbing expertise, special tools and instruments, and a lot of patience. You may be better off paying a plumber to do the job since it can be technically intricate for some.

However, if you do have the skill to do this DIY project, you can save on the plumber expense. The video below shows how to install a Thermostatic Mixing Valve.

How to install a mixing valve

Items you may need:

  • Flat head screwdrivers & pliers
  • Adjustable pipe wrench
  • Safety goggles
  • A reciprocating saw with a metal-cutting blade
  • Tile cutting blade
  • Support blocks, pipe straps
  • Plumbers putty


  1. Turn off the water supply. Remove the handle which controls hot and cold water.
  2. Use the diamond blade to cut the bathroom tiles behind the handle and reach the pipes that you would connect to the existing valve.
  3. Use a reciprocating saw to cut the pipes. Remove the old valve and piping above where you cut, to make way for the new valve to be installed.
  4. Dry fit the new pipes to the cold and hot pipes where the old valve was detached.
  5. Remove the valve spindle of the new valve and disassemble the pipes.
  6. Solder the new valve to the pipes.
  7. Reinstall the spindle which was removed in step 5. Turn on the water and check for leaks (make sure that there is no water flowing out because that can be a costly mistake later on). Adjust the valve if the water is not the right temperature.
  8. Reinstall the old handle.
  9. Turn on your handle and showerhead. Inside the valve is a rotational stop which looks like a gear. This controls how hot the water is allowed to get. Once you adjust this as per your requirement, put the handle back on.
  10. Use plumber’s putty against the rear section of the valve.
  11. Screw the cover plate to the wall.
  12. Slip a rubber gasket behind the escutcheon plate and the shower handle. Tighten the screws. This completes the installation.


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How to Adjust an Anti-scald Valve?

Follow the steps below to adjust an anti-scald valve.

  1. Turn off the water. Before starting anything, make sure to turn off the water to the faucet of the bathtub. Some models will even have a water shut-off provision on the outside of the valve.
  2. Remove the handle. You might need to use a set key or an Allen wrench for this purpose, and it may involve a screw or else a hub.
  3. Remove the valve cover retainer sleeve. The sleeve will usually be protruding out from the center of the valve.
  4. Remove the temperature stop. This would be there on the stem of the valve. Make sure to take note of the side facing out so that you can install it back correctly.
  5. Reinstall the temperature stop. The temperature stop will have multiple settings based on the type and brand of valve used. Adjust the stop according to the setting you need (this might take multiple attempts to understand whether hot is clockwise or anti-clockwise). Once done, place the stop into the correct position.
  6. Put the valve cover back on. You may need to screw it in, depending on the process that you followed earlier.
  7. Replace the valve handle. Take care to fit the cover gently, otherwise, it might break or worse, the handle may get stuck.
  8. Turn the water back on, and enjoy the optimally heated water in the shower!


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Anti-scald valves are meant to provide you with safety against scalding on the one hand and bacteria on the other. Homes with vulnerable age groups such as seniors and children should certainly consider installing them, so as to avoid unnecessary accidents and disease. Apart from anti-scald valves, below are some other precautions that should be taken in order to avoid bathroom incidents due to scalding:

  • Test the water temperature before getting into a bath for at least a few seconds. To prevent accidental scalding, never ever jump directly under the water.
  • Adjust your heater thermostat to between 120- and 140-degrees Fahrenheit.
  • Supervise children and the elderly around hot water. Keep them away from hot liquids as well.
  • Get a plumber or contractor to ensure that pipes, valves, or heaters are regularly checked for wear and tear and are replaced well in time before they become faulty.

We hope that you found this article on how to adjust an anti-scald valve is useful for you.

If you are looking for adaptive bathing equipment for the elderly, you can read our other article on best shower chairs for seniors and adaptive bathroom equipment.