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How to Fix a Leaking Expansion Tank for a Water Heater

An expansion tank protects your home’s plumbing system from potential damage caused by the increased water pressure created by your water heater. The expanding water could possibly backflow into the cold water supply without an expansion tank. The tank is designed to catch the expanding water before it reaches your lines. An expansion tank that leaks from around the fitting where it attaches to the water line can be repaired. If the leak continues, though, you must replace the tank to stop it.

Preparation

Step 1

Turn the valve on your water heater’s water-supply line clockwise to shut the water supply off to the tank.

Step 2

Turn off the breaker in the main panel to shut down an electric water heater.

Step 3

Turn off the gas to a gas water heater by turning the gas control valve to the off position on the water heater.

Replace Thread Seal Tape

Step 1

Remove the existing expansion tank using an adjustable pipe wrench and turning the tank counterclockwise at the top where it attaches to the pipe fitting. Have a partner support the tank to keep it from falling to the floor.

Step 2

Clean the threads on the expansion tank. Remove any dirt, grim or old thread seal tape from the threads with an old cloth.

Step 3

Wrap the threads in two or three layers of new thread seal tape. Reattach the tank to the fitting and tighten it with the pipe wrench

Step 4

Turn the water supply back on to the water heater. Turn on the water or gas, and light the pilot on the gas water heater.

Step 5

Watch for additional leaks from the tank. If your expansion tank continues to leak, you must replace the tank.

Replace the Expansion Tank

Step 1

Turn off all the water faucets inside your residence. Attach a water-pressure test gauge to an outside faucet. Turn on the outside faucet to get the pressure reading. Note the pressure reading on the gauge.

Step 2

Attach a bicycle pump or air compressor to the changing valve at the bottom of a replacement expansion tank if you need to increase the pressure in the tank above 40 pounds-per-square-inch.

Step 3

Check the pressure in the tank with a with a tire-pressure gauge. Add or release air from the expansion tank until the pressure in the tank equals the water pressure in your home.

Step 4

Turn off the water supply to the water heater. Turn off the water gas or electric water heater. Remove the current expansion tank with the adjustable pipe wrench.

Step 5

Wrap the threads of the replacement tank with about three layers of thread seal tape. Screw the tank into the fitting and tighten it with the wrench.

Step 6

Turn on the water supply and the gas or electricity to the water heater.