Anode Rod

An anode rod is a replaceable metal rod, typically made of magnesium or aluminum, threaded into the top of a water heater tank. It's designed to corrode preferentially to the steel tank itself, protecting the tank from rust and pinholes. The rod sits in the hottest part of the tank and slowly dissolves over time—usually 3 to 5 years depending on water hardness, temperature, and mineral content.

In the field, a dead anode rod is one of the fastest ways a water heater fails. Once the rod is consumed, the tank steel begins corroding immediately, leading to leaks that typically aren't worth repairing. Many tanks fail prematurely because the rod was never replaced. Hard water, high temperatures above 140°F, and certain chemical conditions accelerate anode consumption. A replacement rod can add years to a tank's life and is a straightforward upsell.

Always check anode condition during a water heater service call. If it's less than 1/2 inch thick or heavily pitted, replace it. Some rods are flexible or segmented to fit older tanks with tight closures. Magnesium rods work better in soft water; aluminum rods are better in hard water.