Step 1: Determine you have the correct replacement for your relief valve. Match the size, temperature, and BTU rating of the old relief valve. This information is located on the end of the relief valve.
Step 2: Turn the gas control to the pilot setting. This is so the water heater won’t fire while it’s being worked on.
Step 3: Close the cold water supply off to the water heater.
Step 4: Drain off roughly 5-10 gallons of water from the tank. This will bring the water level in the tank below the level of the relief valve.
Step 5: Remove the drip tube from the relief valve.
Step 6: Apply teflon tape to the threads of the new relief valve. In a clockwise direction, when the threads are face up and towards yourself.
Step 7: Remove the old relief valve with a wrench in a counterclockwise direction.
Step 8: Install the new relief valve hand tight first, and then the remainder with a wrench. Ensure the relief valve port is aiming directly down.
Step 9: Teflon tape, and reinstall the drip tube.
Step 10: Open the cold water supply only partially to allow the tank to fill slowly. This will help reduce water hammer.
Step 11: Open a hot faucet preferably at the highest point in the residence. Leave the faucet open as the tank is filling to purge all the air from the system. Once the faucet runs steady water without any air, the faucet can be closed.
Step 12: Open the cold water supply fully, and check for leaks.
Step 13: Turn your gas control back to the on position.