Water Heater Anode Rod: What It Is and How to Replace It

It's important to replace the anode rod in a water heater periodically, but it's a rare homeowner who even knows what an anode rod is let alone how to replace one. That's unfortunate because performing this simple maintenance task is as important as flushing the tank periodically. It can lengthen the life of a water heater by several years — perhaps even double it — and failing to perform it can void the water heater warranty.

An anode rod is designed to corrode and disintegrate inside the water heater tank because by doing so, it spares the metal tank liner from the same fate. It literally sacrifices itself for the sake of the tank liner, which is why it's also known as a sacrificial rod.

Replacing an anode rod is not a complicated job, and you don't need a plumber. You may need to buy or rent an impact wrench, though, because the factory tightens the rod into the tank very tightly, and if you try to loosen it using muscle alone, you could move the tank and break a water connection. Getting the old rod out is the toughest part of the procedure. Installing a new rod is a snap, and if you don't screw it into the tank as tightly as it was screwed in at the factory, the job will be that much easier the next time you replace it.

An anode rod is a metallic rod 3 or more feet long and about 1 1/4 inches in diameter that sits immersed in the water inside the water heater tank. It has a screw cap on one end that fits the threads of an opening in the top of the tank. Most rods are solid, but some are flexible and collapse into several sections, which allows you to insert them and pull them out of tanks that are sitting under shelves or a low ceiling.

A sacrificial anode rod is made of metal that has a higher electrochemical potential than the metal that lines the tank, so it loses electrons to ions in the water faster than the steel liner does, leaving fewer ions to react with the liner. By preferentially exchanging electrons with ions in the water, the anode rod corrodes quickly while protecting the tank liner from rust and corrosion.

Sacrificial anode rods are usually made of magnesium or aluminum plated around a steel core. Both of these metals corrode faster than steel, although magnesium corrodes quicker, and once the rod corrodes completely, the tank will begin to rust. To prevent this, an anode rod should be replaced every three to five years. Some anode rods are made of titanium and deliver a small DC current to the water to charge it. These rods are nonsacrificial; they don't corrode and never need to be replaced.

There's no outward indication of a depleted anode rod, so after about five years, you should simply assume you need one. If necessary, you can perform a visual inspection by following the procedure for removing it without actually doing so. The rod is still serviceable if the surface material hasn't corroded completely, and it isn't completely caked with calcium and hard water deposits that prevent the metal from corroding.

You might want to replace an anode rod that hasn't corroded if you notice sulfurous odors in the hot water. This can be caused by the reaction between a magnesium anode rod and impurities deposited in the water by a water softener installed before the water heater. Installing an aluminum anode rod in place of the magnesium one usually alleviates the odor problem.

The anode rod is inserted through an opening in the top of the water heater tank. On most models, a cap with a hex head nut is plainly visible, but some manufacturers hide this nut underneath a plastic cap that you have to first remove.