How To: Replace a Thermal Expansion Tank

Thermal expansion tanks are a vital part of your home plumbing system and typically last around five to ten years. You may need to replace your current expansion tank if it is filled with water, leaking, rusting or causing water pressure issues in your home.  

To check if your expansion tank is safe to keep, press the valve stem at the bottom, and if air comes out, you can still use it. If water comes out, you will need a new thermal expansion tank. Follow as David Hunt, a master plumber of 35 years, shares his expert advice on the subject.  

What is a Thermal Expansion Tank?  

As the water in your water heater heats up, it expands and creates pressure. This pressure can damage your water lines, so your thermal expansion tank acts as a buffer and gives the pressure a place to go. The rubber bladder inside the expansion tank allows for air to push against one side while the water pressure pushes against the other side, keeping the thermal expansion contained.  

Remove the Old Thermal Expansion Tank  

After determining that you need a new expansion tank, you first need to shut off the main water line. You can find the main shut-off valve in an outside valve box, by your water heater, or on the front wall of your home closest to the street.  

To uninstall your existing thermal expansion tank, use a couple of adjustable wrenches to separate the bottom connection from the pipe. The tank will be heavy, weighing around 20 pounds, so remove it carefully and have a second person there to help if needed. Then, discard the old expansion tank.  

Install the New Thermal Expansion Tank  

To install your Eastman thermal expansion tank, check your home water pressure with a pressure gauge that goes up to 200 psi. This can be tested anywhere after the pressure regulating valve, which includes your back spigot, laundry box and water heater.  

Then, set your expansion tank to this exact psi with an air compressor. This will prevent the diaphragm from rupturing and filling with water. This uneven pressure would weaken the expansion tank, allowing your water pressure to reach up to 80-120 psi. Always test, calibrate and charge your thermal expansion tank to match your home water pressure.  

Then, use Teflon tape and pipe dope to prep the threads on the tank. Then, hand-tighten your tank back onto the pipe and finish it with adjustable wrenches. For more security, especially when installing with PEX pipe, use a HoldRite Quick Strap Expansion Tank Mounting Bracket to secure the expansion tank to the wall.  

After installing your tank, turn your main water line back on slowly. Then, bleed the air out of the system and check for leaks.  

Read More: How To: Replace a Gas Water Heater