A mixing valve is an important component on a water heater that helps regulate the temperature of the hot water supply in your home. It mixes hot water from the tank with cold water from the main supply to deliver water at a safe and comfortable temperature to your fixtures. Let’s take a closer look at what mixing valves do and why they’re an essential part of modern water heater systems.
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The Purpose of a Mixing Valve
Hot water heaters heat water to very high temperatures, often between 120-140°F. This hot water then flows into the home’s plumbing system and to faucets and fixtures when needed. However, water over 125°F can cause serious scalding injuries. This is where the mixing valve comes in – its job is to bring down the hot water temperature to a safe level before it reaches your fixtures.
The main purposes of a mixing valve are:
- Prevent scalding – Mixing valves blend hot tank water with cold water to deliver a safe outlet temperature below 120°F to fixtures. This prevents accidental scalding.
- Compensate for fluctuations – The valve automatically adjusts to compensate for temperature fluctuations in the tank so a steady outlet temperature is maintained.
- Meet code requirements – Plumbing codes require water heaters to have a mixing valve to limit hot water temperatures as a safety measure.
How a Mixing Valve Works
A mixing valve is a specialized mechanical valve that blends hot water with colder water in controlled proportions to achieve a set outlet temperature. Here is an overview of how it works:
- Hot water from the tank enters the mixing valve.
- Cold water also flows into the valve through a separate inlet.
- Inside the valve, a thermally-sensitive wax motor or piston senses the hot water temperature.
- If the hot water exceeds the valve’s set temperature limit, the wax motor expands or the piston rises. This increases the flow of colder water into the mix.
- Conversely, if the hot water is cooler, the wax motor or piston adjusts to reduce cold water flow and maintain the set outlet temperature.
- The mixed water, now at a safe 120°F or less, flows out of the valve and into the plumbing system.
This process of hot-cold water mixing happens automatically inside the valve whenever hot water is called for. The mixing valve reacts to temperature changes and continually balances the flows to maintain the set outlet temperature. Advanced electronic mixing valves can even monitor and respond to sudden pressure or temperature changes within a fraction of a second.
Types of Mixing Valves
There are two main types of mixing valves commonly used with residential and commercial water heaters:
Thermostatic Mixing Valves
Thermostatic mixing valves (TMVs) use a temperature-responsive wax motor or liquid-filled thermostatic element. As hot water enters and heats the wax or liquid, it expands and pushes a piston to modulate the cold water intake and mix the flows. TMVs maintain outlet temperatures within +/- 3°F.
Key features:
- Precise temperature control
- No external power source required
- Pressure balancing models available
- Easy to adjust outlet temperature setting
Electronic Mixing Valves
Electronic mixing valves (EMVs) use advanced microprocessor-controlled actuators and temperature sensors to automatically adjust hot and cold flows. The electronic controller lets EMVs react faster and more accurately than TMVs.
Key features:
- Very accurate temperature control (+/- 1°F)
- Faster response to temperature changes
- Digital display and control panel
- Error and high temperature alarms
- Require electrical power to operate
Mixing Valve Requirements
For safety reasons, plumbing codes require water heaters to be equipped with an approved mixing valve under certain conditions. Key mixing valve requirements per the International Plumbing Code (IPC) include:
| Condition | Mixing Valve Requirement |
|---|---|
| Water heaters above 140°F | A TMV or EMV is required |
| Point-of-use water heaters | A TMV is required at each fixture |
| Water heaters in public facilities | An EMV is required |
| Water heaters in nursing homes and schools | An EMV is required |
Always check local plumbing codes for the mixing valve requirements in your area. Any newly installed or replaced water heater must have an approved mixing valve.
Mixing Valve Locations
Proper location is important for mixing valves to work correctly. Here are some typical installation locations:
- At the water heater: This is the most common location. The mixing valve is installed in the pipe connecting directly to the water heater outlet.
- At the fixtures: Point-of-use mixing valves are installed under sinks or at other fixtures. This allows tailoring water temperature to each location.
- Central manifold: Larger plumbing systems may have a central manifold with the mixing valve located before branching out to different zones.
The mixing valve should be installed as close to the water heater as possible. This allows it to respond faster to temperature fluctuations. Always follow manufacturer instructions for the best location in each application.
Adjusting the Mixing Valve Temperature
One important task is setting and adjusting the outlet temperature on the mixing valve. A properly adjusted valve will maintain a consistent temperature between 105-120°F. Follow these steps:
- Turn on a hot water faucet and let the temperature stabilize.
- Measure the temperature using a digital thermometer.
- Locate the adjustment knob on the mixing valve.
- Turn the knob to raise or lower the temperature as needed.
- Recheck the faucet temperature and adjust as needed until in the 105-120°F range.
For electronic mixing valves, the temperature is adjusted using buttons on the digital display instead of a knob. Always check official instructions for your specific mixing valve.
Maintenance Tips
Mixing valves are generally maintenance-free. But here are a few tips to keep yours working properly:
- Check water temperatures monthly and adjust the valve as needed.
- Inspect for leaks annually and repair any drips or weeping.
- Clean the valve screens every 1-2 years to remove debris and mineral buildup.
- Exercise the valve by cycling it from hot to cold several times per year.
- Replace thermostatic elements every 5-8 years or per manufacturers’ schedule.
Electronic valves may also require periodic calibration as part of a preventive maintenance schedule. Always refer to the manufacturer instructions for your specific model.
Signs of Mixing Valve Problems
Faulty mixing valves can cause serious problems like scalding water or unstable temperatures. Watch for these signs of mixing valve issues:
- Hot water temperature exceeding 125°F
- Frequent spikes in hot water temperature
- Fluctuating water temperatures
- Reduced hot water flow
- Leaking from valve body
- Error codes or alarms on electronic valves
If you notice any of these signs, turn off the water heater and have the mixing valve inspected by a professional. Catching problems early prevents more extensive damage or dangerous failures.
Replacing a Mixing Valve
Mixing valves do wear out over time. Old valves with stuck pistons or failed thermostats cannot keep temperatures consistent. Some signs it’s time to replace the mixing valve:
- Outlet temperature cannot be properly adjusted
- Frequent temperature fluctuations
- Valve is over 10-15 years old
- Parts are corroded or damaged
Replacing a faulty mixing valve restores accurate temperature control. Turn off the water and drain the heater before removal. Take measurements and photos to get the same model or size replacement valve. Follow installation instructions carefully when swapping in the new mixing valve.
Conclusion
Mixing valves play an important safety role on water heaters by regulating output temperatures. They mix hot tank water with cold supply water to deliver a temperate output that prevents scalding. Thermostatic and electronic valves automatically maintain set temperatures. Mixing valves are required by code on most residential and commercial heater installations. Proper maintenance and adjustment ensures mixing valves work reliably for years. But valves that exhibit problems like leaks or temperature spikes should be replaced immediately to avoid safety hazards.