How a Thermal Expansion Tank is Key To Your Home’s Safety

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A thermal expansion tank (or valve) is designed to protect your home from leaks and damage caused by pressure buildup when water heats up. Here’s why it matters: as water gets hotter, it expands. In many modern plumbing systems, backflow prevention devices or check valves create what’s called a “closed system.” That means the extra volume of water has nowhere to go, and the pressure inside your pipes starts to rise.

Without a way to relieve that pressure, your plumbing system takes the hit—leading to dripping faucets, leaking pipes, or even a damaged water heater. Think of it this way: when water heats up, it needs more space. If it doesn’t have it, something else in your plumbing system will give.

That’s where a thermal expansion tank comes in. Installed near your water heater, it gives the expanding water a safe place to go, keeping pressure balanced and protecting your pipes, fixtures, and water heater from unnecessary wear and tear.

What is a Thermal Expansion Valve?

A thermal expansion valve (often called a TEV) helps protect your plumbing by releasing pressure when it gets too high. As water heats up, it expands. If that extra pressure inside your plumbing system goes beyond the safe limit, the valve opens and lets out a little water to bring the pressure back down.

It’s normal for the pipe connected to this valve to drip occasionally when pressure builds. But if you see a steady stream of water coming from it, that’s a sign of a bigger problem. Many homeowners call us worried about a “leaking pipe” outside—it looks like a running faucet, but it’s really the valve doing its job under too much pressure.

In most cases, the valve will need to be replaced if it’s been forced open by high pressure. But replacing the valve alone isn’t the real fix—you also need to address the underlying pressure problem. Just as important, the drain line connected to the valve must be installed correctly so water is carried away safely. If that line isn’t code-compliant, water can pool near your foundation or inside your home, causing damage and creating safety hazards.

Benefits of a Thermal Expansion Valve

Pressure Relief: Automatically releases pressure, safeguarding your plumbing system.
Protection for Fixtures and Appliances: Prevents excessive pressure that could damage water heaters, faucets, and other fixtures.
Cost-Effective Solution: Simple to install and maintain, making it an affordable way to address thermal expansion.

What is a Thermal Expansion Tank?

A thermal expansion tank is another way to deal with the extra pressure created when water heats up. Instead of releasing water like a thermal expansion valve, the tank is built to absorb that added volume safely. Inside the small tank is a flexible bladder that separates the water from a cushion of air. As the hot water expands, the air compresses and gives the extra water somewhere to go. This keeps pressure steady in your plumbing system and takes the strain off your pipes and water heater.

Many homeowners choose thermal expansion tanks because they provide reliable, long-term protection without wasting water.

Benefits of a Thermal Expansion Tank

Steady water pressure: Absorbs expanding water so your system maintains consistent pressure.
Protects your appliances: Reduces stress on your water heater, pipes, and fixtures, helping them last longer.
Saves water: Unlike a valve that discharges water, the tank stores the extra volume, making it an efficient and environmentally friendly option.

Comparing Thermal Expansion Valves and Tanks

While both devices address thermal expansion, their methods differ:

Thermal Expansion Valves: Release water to relieve pressure. Cost-effective but may result in water waste because when water drips to relieve pressure, it is lost to the plumbing system.
Thermal Expansion Tanks: Store the expanded water, maintaining pressure without water loss. They require slightly more space and initial investment but provide a reliable and sustainable solution.

How Do You Know You Have a Problem with Your Pressure?

Signs of High Pressure: Dripping faucets, banging pipes (water hammer), or frequent activation of the water heater’s relief valve. In other words, you may see water running out of your thermal relief valve. Customers often call us stating that a pipe that comes out of their home is leaking.
What is Normal Pressure? The International Plumbing Code states that residential plumbing systems operate efficiently at a pressure of 60-80 psi (pounds per square inch).
What Should You Do If Your Pressure Is High? If you suspect excessive pressure, take immediate action by checking the pressure and consulting a plumbing professional.

How Do You Check Your Pressure?

Properly regulated pressure is essential to a healthy plumbing system. High pressure can lead to pipe bursts, running toilets, dripping faucets, and even shorten the life of your water heater. The water pressure in your home is maintained by your pressure regulating valve. While these can be adjusted to some degree, if you find that you have very high pressure, your valve has likely failed and needs to be replaced.

You can check your water pressure with a simple water pressure gauge. Just screw the gauge onto an outdoor faucet or hose bib, turn on the water, and read the dial. For the most accurate result, make sure you’re testing from a faucet that’s located after your pressure regulating valve (PRV). For example, a hose bib in the front yard often isn’t after the PRV, which means the reading will always look higher than what’s actually inside your home.

Be careful if you try to test from the boiler drain on your water heater—older drains don’t always close tightly again once they’ve been opened.

For the reading to be accurate, there can’t be any water running inside the home. Make sure faucets, showers, dishwashers, and washing machines are all turned off. If there’s an active leak in the system, fix that first, since running water will throw off the results (and could cause more damage if left unchecked).

If your water pressure reading is higher than 80 psi, it’s time to call a plumber. In most cases, that means your pressure regulating valve needs to be replaced.

Case Study: Resolving Thermal Expansion Issues in Duluth, GA

Recently, a homeowner in Duluth, GA, contacted us while preparing to sell their home. During the buyer’s inspection, the plumbing system did not pass due to a failing thermal expansion tank. The inspection revealed high water pressure that needed immediate attention to meet code compliance.

Our team quickly identified the root cause of the problem: a faulty pressure regulating valve (PRV). The high pressure was not only causing strain on the plumbing system but had also rendered the existing thermal expansion tank ineffective. To resolve the issue, we replaced the pressure regulating valve, effectively bringing the water pressure back to a safe range. We also installed a new thermal expansion tank, ensuring the entire system met code requirements and functioned reliably for the new homeowners.

old leaking expansion tank to be replaced — The old leaking thermal expansion tank to be replaced

a new expansion tank replacing the old leaking expansion tank — The old leaking thermal expansion tank to be replaced

Thanks to these repairs, the home’s plumbing system was compliant and ready for sale, providing peace of mind for both the seller and the buyer. This case highlights the importance of addressing high pressure problems promptly and ensuring that all components, such as expansion tanks and PRVs, are functioning correctly.

Both thermal expansion valves and tanks are valuable tools in protecting your plumbing system from the damaging effects of thermal expansion. If you’re unsure which option is right for your home, consult a licensed plumber to assess your system and recommend the best solution. Thermal expansion tanks, in particular, offer a sustainable and reliable way to safeguard your plumbing from the risks of pressure build-up.