How often should you check the water heater anode rod?

Short answer

Inspect the water heater anode rod every 3 to 5 years. With a water softener, check it every 1 to 2 years, because softened water uses the rod up faster. The anode is a metal rod that hangs inside the tank and corrodes on purpose, so the steel tank doesn't. When it's eaten down to a bare wire, the tank starts rusting instead. Pulling it to look takes 30 to 60 minutes, and a new rod costs $20 to $50.

Why it matters

A water heater tank is steel with a thin glass lining, and the lining isn't perfect. Wherever it's cracked or thin, water reaches steel, and steel in hot water rusts. The anode rod stops that through plain chemistry: it's made of a metal that corrodes more readily than steel, so the water attacks the rod and leaves the tank alone. It's called a sacrificial anode because it's there to be used up.

Once the rod is gone, nothing protects the tank. Rust spreads from every flaw in the lining, the water turns the color of weak tea, and within a few years the tank leaks and has to be replaced. Replacing a rod costs $20 to $50; replacing the heater costs $1,200 to $5,000. The rod is the one part that decides whether a tank heater reaches the top of its 8 to 12 year life or fails early, and it's the part almost nobody checks.

When to do it more often

A water softener is the main reason. Softened water is more corrosive to the anode, so a rod that would last years in hard water can be gone in 1 to 2 years. If you have a softener, check the rod on that schedule.

A tank that's already past the middle of its life and hasn't had the rod checked should get a look now, whatever the date. If the first inspection finds the rod mostly gone, replace it and check again sooner than the usual interval, since it's a sign the water is hard on anodes.

What you need

A 1-1/16 inch socket with a breaker bar, because the rod's hex head is tight and large
A garden hose, to drain a little water from the tank before you pull the rod
Teflon tape for the threads of the new rod
A replacement anode rod, in a flexible, segmented style if there isn't room above the tank to lift a straight one out

Steps at a glance

Turn the heater off, close the cold water inlet, and open a hot tap in the house.
Drain a few inches of water out of the tank through the hose so it doesn't spray when the rod comes out.
Find the rod's hex head on top of the tank, often under a plastic cap, and break it loose with the socket and breaker bar.
Lift the rod straight up and out, and look at it.
If it's eaten down to the core wire or coated in hard calcium, wrap the new rod's threads with tape and screw it in.
Close the drain, open the cold inlet, and let the tank fill until the hot tap runs steady.
Turn the heater back on and check the hex head for leaks.

You're done when the tank is full, the tap runs without spitting, and the new rod's head is dry.

Signs it's overdue

A rotten egg smell in the hot water only, from bacteria reacting with a worn rod.
Rusty hot water, which means the tank is already corroding.
A tank older than 5 years whose rod hasn't been looked at.

DIY or pro

This is a moderate job, and the hard part is physical. The hex head has been in place for years and takes real force to break loose, and the tank may shift if it isn't braced. A long breaker bar, a helper to steady the tank, and sometimes a short burst of penetrating oil get it done. Headroom above the tank is the other issue: a straight rod is as tall as the tank, and if there isn't room to lift it out, a segmented rod bends around the problem.

A plumber charges $150 to $300 to inspect and replace the rod, and will often do it during a flush or a relief valve check. If the hex head won't move for you, or the tank sits in a closet with no room to work, that's the call.

Safety

Gas: set the gas control to pilot or off before you drain the tank, and don't turn the burner back on until the tank is full.
Hot water under pressure: the tank holds hot water under house pressure. Open a hot tap before you drain, and drain a few inches before loosening the rod, or hot water sprays out of the opening when the threads let go. Let the tank cool if you can wait.

FAQ

How do I know if the anode rod needs replacing?

Pull it out and look. A good rod is a thick metal bar. A spent one is a thin wire, often with bits of crust hanging on it. Replace it when it's mostly wire.

Can I replace a water heater anode rod myself?

Yes, if you can break the hex head loose and have room above the tank. A segmented rod solves the headroom problem.

Why does my hot water smell like rotten eggs?

Bacteria in the tank react with a worn anode and make hydrogen sulfide gas. A new rod, often one of a different metal, usually ends the smell.

Does a tankless water heater have an anode rod?

No. There's no tank to protect. Tankless units need descaling instead.