What does an anode rod do, and when should it be replaced?

What the anode rod does

A tank water heater is a steel tank with a protective lining, but no lining is perfect. Water reaches small spots of bare steel, and steel in water corrodes. The anode rod is there to corrode first. Bradford White describes it as a "sacrificial" rod that is consumed as it gives up its electrons to protect the carbon steel tank^[1].

Once the rod is used up, the tank itself starts to rust. Rheem calls the anode the part that protects the tank from internal corrosion, puts typical tank life at 8 to 12 years, and lists anode replacement among the maintenance that helps a tank reach it^[3]. That makes a $20 to $50 part^[4] one of the cheapest ways to extend the life of a heater that costs far more to replace.

The rod usually threads into the top of the tank, either in its own port under a cap or built into the hot water outlet fitting. The exact spot depends on the brand and model.

Types of anode rods

Type	How it works	When makers use it
Magnesium	Gives up electrons most freely; Bradford White calls it the leading material for protecting the tank[1]	Most standard water conditions
Aluminum (or aluminum alloy)	Less reactive, so it wears more slowly in conductive water	Softened water or low pH, where magnesium is consumed too fast[1]
Zinc-aluminum blend	An aluminum rod with some zinc	Often sold for rotten-egg odor problems; HomeGuide notes zinc rods help minimize odors[4]
Powered (impressed current)	Uses a small electric current from an outlet instead of sacrificial metal	Odor problems or aggressive water; confirm your maker allows it

Bradford White notes that water chemistry decides how fast a rod wears: softened water raises conductivity, low pH speeds up the reaction, and dissolved solids, sulfur and bacteria also matter^[1]. That is why the same heater can need a new rod after a few years in one house and much later in another.

Signs the anode is worn out or wrong for your water

Bradford White lists three symptoms that point to the anode^[1]:

1. Air or sputtering from the hot tap when it is first opened.
2. Smelly hot water, often a rotten egg odor.
3. Discolored or cloudy hot water.

For air in the lines, Bradford White's fix is a less reactive rod: magnesium to aluminum, or aluminum to an aluminum alloy^[1]. For a sulfur smell, see rotten egg smell in hot water. Rusty hot water can also mean the anode is spent and the tank is starting to corrode.

How often to check it

Source	Inspection	Replacement
A.O. Smith	Inspect annually[2]	When deteriorated or several inches of core wire show[2]
Rheem		Every 3 to 4 years[3]
HomeGuide, citing plumbers		Every 3 to 5 years[4]

A.O. Smith's test is simple: a rod in good shape is smooth and about a half inch in diameter. Replace it if it is visibly deteriorated or if several inches of the steel core wire are exposed^[2]. Many owners pair the check with the yearly tank flush, since the tank is already shut down. See the maintenance checklist.

Myth: pull the anode to stop the smell

Removing the anode is common advice online for rotten-egg odor. It does stop the smell, because the magnesium rod supplies the hydrogen the odor-causing bacteria need. But Bradford White states plainly that complete removal of the anode will void the warranty and shorten the life of the tank^[5]. The fix Bradford White describes is chlorinating the tank and switching to an approved anode type, not running without one^[5].

Can you replace it yourself?

Some owners do. It usually means shutting off the cold supply and the gas or power, relieving pressure, draining a few gallons, and breaking loose a fitting that may not have moved in years. Rods are often tight enough to need a long breaker bar, and the force can twist the tank on its connections. A full-length rod also needs headroom above the tank; segmented or flexible rods exist for low ceilings.

Two rules apply whether you or a plumber does the work:

• Use a rod your heater's maker approves, in the right length and material for your water.
• Never leave the tank without an anode^[5].

If the fitting will not budge, the tank is old, or the rod is fused to the tank, stop. A plumber can judge whether the heater is worth the work. A heater near the end of its life may not be.

What it costs

HomeGuide's national figures (August 2025)^[4]:

Item	Cost
Anode rod replacement by a plumber	$150 to $350
Anode rod part only	$20 to $50
Tank flush by a plumber	$75 to $250

Combining the anode check with a flush in one visit usually costs less than two trips. See anode rod replacement cost.

When to call a pro

• The fitting will not turn, or the tank shifts when you apply force.
• The rod is gone to bare wire and the heater is past 8 to 10 years old: ask whether repair still makes sense.
• Rotten-egg odor that returns, where chlorination and an anode change are needed together.
• Rusty hot water or any leak around the top fittings.