Water Heater Anode Rod Replacement: Extend Your Tank’s Life

Last updated: July 2026 · Reviewed against A.O. Smith and Rheem service documentation

The anode rod is the single most important part for extending your water heater’s life — and the most overlooked. This “sacrificial” metal rod corrodes instead of your tank, so when it is used up, the tank itself starts to rust. Replacing a $20–$40 anode rod every few years can double the life of the tank. Here is how to check it, when to replace it, and how to do it yourself.

What an Anode Rod Does

Inside every tank water heater is a long metal rod — usually magnesium or aluminum — threaded into the top. Through simple electrochemistry, this rod attracts the corrosive elements in water and corrodes in place of the steel tank. That is why it is called a sacrificial anode: it sacrifices itself to protect the tank. Once the rod is fully consumed, there is nothing left to protect the steel, and the tank begins to rust from the inside — the leading cause of tank failure.

When to Replace the Anode Rod

Inspect the anode rod every 2–3 years, and replace it when it is heavily corroded. Signs it needs checking or replacing:

• The tank is 3+ years old and the rod has never been checked
• Rotten-egg (sulfur) smell in the hot water — often a depleted magnesium rod reacting with bacteria
• Rust-colored hot water
• The rod is under half an inch thick, or the steel core wire is exposed

In hard water areas, rods deplete faster — check yearly. A rod checked and replaced on schedule is the cheapest insurance against a leaking tank.

How to Replace an Anode Rod

1. Turn off power/gas and the cold water supply — see how to turn off your water heater.
2. Drain a few gallons from the tank (attach a hose to the drain valve) to drop the level below the top.
3. Find the anode rod’s hex head on top of the tank (sometimes under a plastic cap). Use a 1 1/16″ socket and a breaker bar — it is often very tight.
4. Unscrew and remove the old rod. If clearance above the tank is tight, use a flexible/segmented replacement rod.
5. Wrap the new rod’s threads with PTFE tape, screw it in, and tighten firmly.
6. Close the drain, refill the tank (open a hot tap to release air), check for leaks, then restore power/gas once full.

The rod costs $20–$40. The only tricky parts are breaking the tight factory torque and having enough overhead clearance — segmented rods solve the clearance problem.

Magnesium vs. Aluminum vs. Powered

• Magnesium: best protection, standard choice; may cause sulfur smell in some water.
• Aluminum: lasts longer in hard water and resists the smell, but less protective.
• Powered (electronic): never depletes, ideal for smelly water or very hard water; higher upfront cost, no replacement needed.

If you get a rotten-egg smell, switching from magnesium to aluminum or a powered rod usually solves it.

FAQ

How often should you replace a water heater anode rod?

Inspect it every 2–3 years and replace it when it is heavily corroded or under half an inch thick. In hard water areas, check yearly. Regular replacement can double the tank’s lifespan.

What happens if you don’t replace the anode rod?

Once the rod is fully consumed, the corrosive elements attack the steel tank instead. The tank rusts from the inside and eventually leaks — the most common cause of water heater failure. A $30 rod prevents a $1,500+ replacement.

Why does my hot water smell like rotten eggs?

Usually a magnesium anode rod reacting with sulfur bacteria in the water. Switching to an aluminum or powered anode rod typically eliminates the smell, as does disinfecting the tank.