Replacing the rods as they wear out will considerably extend the life of your water heater. The useful life of the rod will depend on your water quality--softened water may eat through an anode rod in as little as six months. If you don't soften your water, check the anode rod every year and replace it if it has corroded down to the core in sections of 6 inches or longer.
Turn off the electricity or gas to the heater.
Turn off the water to the heater, and open a hot water connection for a minute to relieve pressure.
Spray on WD-40 and loosen the hex nut on top of your water heater; this is the top of the anode rod.
Remove the old rod. You may have to bend it to get it out of the tank. follow these steps to remove the rod.
Shut down the water supply. Open a hot-water faucet on the same water line to relieve pressure within the water heater. If water continues to run, your water is not shut off. Drain a little water from the tank until the level goes down a few inches.
Examine the top of the water heater for the top of the anode rod (spud) or connecting hardware. Some water heaters, particularly those with longer warranties, have multiple anodes. Look for the sacrificial, or corroding, anode. It may be under a cap, about halfway in toward the center (not on the outside edge). The anode may be under a pink-top nipple. If you don't see a spud or connector, remove the top of the water heater. (Very occasionally, the anodes are under a sheet-metal cover that has been foamed into place, requiring you to drill through the top---but not far---and poke around with a screwdriver to find the anodes.)
Apply penetrating oil generously to the connecting nut or threads of the anode rod, which is hanging vertically from the top of the water heater. Allow the penetrating oil time to work.
Loosen the anode carefully with a wrench. Corroded anodes are brittle.
Remove the anode. If there isn't enough clearance to withdraw the anode straight up, carefully bend it into a curve while pulling from the water heater.
Disconnect the water heater from its plumbing and gas or electric connections if you cannot bend the anode enough to remove it without cutting or breaking. Drain enough additional water from the water heater tank so you can tip it sideways. Remove the anode. (Or, consider pulling the anode out a little at a time, securing its position, cutting above that point, and repeating until the anode has been removed completely.)
Wrap the threads of the new anode rod with Teflon tape. This will make it easier to remove later. If you have very low clearance over your water heater, buy a flexible anode rod. Insert the rod into the tank and screw it tight.
Turn the water back on, followed by the electricity or gas.
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