Updated On: September 10th 2025
You use running water in your home every day. When you reach for the knobs or handle that controls the flow of water into a sink, shower, or bathtub, you have the option to get cold or hot water, or a blend of both. You probably know the exact combination of the two that’s the most pleasant for you.
But did you know that there’s a hidden mechanism in your plumbing to make sure that you don’t get an unpleasant surprise of extremely hot water? It’s called the mixing valve, and without it, your daily supply of water could become dangerous.
What is a Mixing Valve and How Do They Work?
The term “mixing valve” has the general application of meaning any device in plumbing that controls the mix of hot and cold water. While this provides a comfortable temperature, in most cases, a mixing valve isn’t designed simply for comfort; it serves as a critical safety mechanism that will keep you from accidental scalding due to high temperatures.
How a Mixing Valve Protects Your Family
The danger of scalding water from your plumbing exists because water in a home needs to be stored at high temperatures (often 120°F or more) to prevent bacterial growth. Without the regulation of a mixing valve, this water might flow directly from your shower head or faucet and cause you injury.
Types of Mixing Valves: Thermostatic vs. Pressure Balance
While they serve a similar purpose, there are two main types of valves used in modern plumbing systems:
- Thermostatic Mixing Valves (TMVs): These valves use a thermostat to sense and control the water temperature. They automatically adjust the mix of hot and cold water to maintain a constant temperature, even if the pressure or temperature of the incoming water supply changes. These are often used for whole-home systems or in high-use areas like master showers.
- Pressure Balance Valves: This is the most common type found in modern showers and bathtubs. It works by sensing the pressure ratio of hot to cold water. If there’s a sudden drop in cold water pressure (like when a toilet is flushed), the valve immediately reduces the hot water pressure to match, preventing a surge of scalding water. It maintains the balance of pressure, not a specific temperature.
4 Common Signs of a Failing Mixing Valve
Like any mechanical part, a mixing valve can wear out over time. If you notice any of these issues, it’s a strong sign that your valve needs professional attention:
- Extreme Temperature Fluctuations: The water temperature fluctuates wildly, from very hot to very cold, without you touching the handle.
- Loss of Water Pressure: A blocked or failing valve can restrict water flow to the faucet or shower.
- The Handle is Stuck or Leaking: You can’t turn the handle, or you see water dripping from around the handle plate.
- Only Hot or Cold Water: The valve is stuck on one side and no longer blends water properly.
Trust Your Plumbing to the Professionals
Because a mixing valve is so important for protecting you and your family, whether showering, doing the dishes, or washing your hands, you need to take good care of your plumbing. If you’re experiencing any of the issues above, it’s time to call a professional.
The licensed plumbers at Modern Plumbing Industries have the expertise to inspect, repair, and replace all types of mixing valves. A visit from one of our local plumbing professionals will ensure your system is safe and provide peace of mind. You can fill out our form to have a member of our team get in touch with you about scheduling an inspection or repair.