An expansion tank is a small tank installed on the water line near your water heater. It gives water room to expand as it heats, which helps prevent pressure from building up in the heater and pipes.
Why Water Needs Room to Expand
Water expands when it is heated. In many homes, a check valve or pressure-reducing valve on the main line keeps water from flowing back to the street. That creates a closed system. With nowhere to go, the extra volume from heated water raises the pressure in the pipes every time the heater runs.
How an Expansion Tank Works
Inside the tank, a rubber bladder separates water from a cushion of air. When water expands, it pushes into the tank and squeezes the air. When you open a faucet and pressure drops, the water flows back out. This keeps pressure steadier throughout the system.
Signs You May Need One or It May Be Failing
- The water heater relief valve drips or releases water
- Faucets spray hard right after the heater runs
- Banging or knocking in the pipes
- Toilets that run briefly for no reason
- The expansion tank feels full of water when tapped, instead of sounding hollow at the top
Expansion tanks can fail when the bladder tears or loses its air charge. A waterlogged tank no longer protects the system and usually needs to be replaced.
Protecting the Heater and Fixtures
Repeated pressure spikes wear out the water heater, relief valve, faucet parts, and appliance hoses. In some areas, codes require an expansion tank when a closed system exists. A plumber can test your pressure and check whether your tank is working.
If the relief valve is dripping or the heater seems strained, checking the heater and its expansion tank can find the cause. If you are unsure whether your home has a closed system, you can ask about the water pressure in your pipes at (833) 603-1840.