How Does a Thermostatic Mixing Valve Work?

Last Updated on October 31, 2021 by Bonnie C. Welling

The thermostatic mixing valve is a necessary component for the bathroom. It blends hot water with cold water and ensures the water’s final temperature is safe for human usage. You may also know this machine as TMV. Proper maintenance of this gadget is highly required to keep it usable for a long time.

To use and install it correctly, knowledge about how does a thermostatic mixing valve work is necessary. You should also know about all the parts of this thermostatic mixing valve. Hopefully, with proper maintenance, you will be able to use it for an extended period.

How Does a Thermostatic Mixing Valve Work?

Main Components of a Thermostatic Mixing Valve 

A thermostatic mixing valve comes with many internal parts for blending hot water with cold water. There are a total of seven essential portions in a thermostatic mixing valve. Those seven crucial parts are:

  • Hot water inlet port 
  • Cold-water inlet port 
  • Thermostat element 
  • Slide valve 
  • Hot valve seat 
  • Cold valve seat
  • Mixed water outlet 

How Does a Thermostatic Mixing Valve Work – The Phase-Wise Processes

Those seven parts above take full responsibility for blending hot and cold water. This whole process makes sure the water you will use to shower comes at a suitable temperature. The phase-wise working processes of this machine are:

Phase-1: Water Supply

There are two ports available on both sides of the thermostatic mixing valve for water supply. Those two ports are known as the hot water inlet port and the cold water inlet port. As their names suggest, they are for supplying hot and cold water respectively. 

The hot water port will be connected to the water heater. On the other hand, a cold water port needs a connection with a regular water supply.

Phase-2: Internal Connection

There will be a slide valve in the middle of the thermostatic mixing valve. When water comes through the inlet ports, water has to go through this part. The hot valve seat will connect the hot water inlet port with the small hole of the slide valve. 

It will be on the lower part of the slide valve, also known as the piston. On the other hand, the cold valve seat will connect the cold-water inlet port with the other hole. It will be on the upper portion of the piston. Both these holes will take water at the blending section. 

Phase-3: Water Blending

A thermostat element will be present at the piston as the heat sensor. The water will constantly flow through the hot water inlet port and the cold-water inlet port. Then, water will try to flow below to the blending part through both the valve seats. But the sensor will control the water flow of both these sides.

When the sensor feels the necessity of hot water, it will shut the cold-water valve seat. So, only the hot water will flow to the blending part. Similarly, when there is the necessity of cold water, the piston will shut the hot valve seat. This action will let the cold water flow down. 

The required hot and cold water will continue to flow in that part, and they will mix. The blended water temperature will be suitable because of the heat sensor situated above.

Phase-4: Supplying Blended water through the mixed water outlet

All the parts in the thermostatic mixing valves will make sure the suitable temperature of the water. Then that water will flow to the shower pipe for your usage. And hopefully, you will get the perfectly blended water at your suitable temperature.


Thermostatic Mixing Valve Regulations

The necessary regulations to follow are: 

  • Depending on the appliance, the blended water temperature should remain within 38-45-degree Celsius
  • Field-testing is highly required in every 12-month cycle to keep the machine efficient
  • The pressure in the thermostatic mixing valve should stay within 0.2 bar to 10 bar

Thermostatic Mixing Valve Problems

The problems that you may need to face while using a thermostatic mixing valve are:

  • The water temperature may not be suitable as per your requirement
  • Water flow in any section can face interruption
  • The thermostatic mixing valve pipes can get leaked or dripped as well.


A thermostatic mixing valve is a necessary gadget for the bathroom of your house. It will mix both hot water and cold water, and keep the temperature of that mixture suitable for you. When you take a bath with perfectly blended water, you will feel much fresh. 

You can install it all by yourself when you know the processes of how does a thermostatic mixing valve works. When any repair is necessary, you can do it easily with your knowledge in this sector. If you take proper care of this machine, it will serve you long.

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