Water Heater Anode Rods: What They Do and When to Replace Them
How the anode rod protects your tank from rust, how often to check it, the different types, and how it can fix rotten-egg smelling hot water.
In this guide
The anode rod is a metal rod inside your water heater that corrodes on purpose so the steel tank doesn’t. Once it’s used up, the tank starts to rust from the inside. Have it checked every few years and replace it when it’s heavily corroded or the core wire is exposed. If your hot water smells like rotten eggs, switching from a magnesium rod to an aluminum-zinc or powered anode often fixes it.
Every tank water heater has a part that’s designed to be eaten away: the anode rod. It’s inexpensive, easy to overlook, and one of the main reasons some water heaters last much longer than others.
What does an anode rod do?
The inside of a water heater tank is steel lined with glass, but the lining always has tiny gaps. Water is corrosive, so those spots would rust. The anode rod, usually made of magnesium or aluminum around a steel core wire, is more reactive than the tank. The water attacks the rod instead, and the tank is protected. This is called sacrificial protection. As long as there’s enough anode left, the tank stays protected.
How often should you check the anode rod?
Every two to three years is a common recommendation, and more often if you have a water softener or very hard water. Softened water tends to use up anode rods faster. Many heaters come with a 6-year warranty, and their anode rods are often significantly depleted by around that age.
Signs your anode rod needs replacing
- The rod is heavily pitted, thin, or the steel core wire is showing along much of its length.
- Rusty or discolored hot water, which can mean the tank itself has started to corrode.
- Rotten-egg smell from the hot water only (see below).
- The heater is several years old and the rod has never been checked.
Types of anode rods
| Type | Good for | Notes |
|---|---|---|
| Magnesium | Most water conditions | Strong protection; can react with certain water to cause a sulfur smell |
| Aluminum or aluminum-zinc | Hard water, sulfur smell problems | Zinc helps control the rotten-egg odor |
| Flexible (segmented) | Low ceilings | Bends so it can be installed with limited overhead clearance |
| Powered anode | Persistent odor problems, long-term protection | Uses a small electric current instead of being consumed; plugs into an outlet |
Rotten-egg smelling hot water
If your hot water smells like rotten eggs but the cold water doesn’t, the cause is often a reaction between bacteria in the water and a magnesium anode rod, which produces hydrogen sulfide gas. Common fixes include replacing the rod with an aluminum-zinc or powered anode and disinfecting the tank. If both hot and cold water smell, the problem is more likely in the water supply itself.
Don’t remove the anode rod to stop a smell. Without it, the tank loses its corrosion protection and can fail early, and it may affect your warranty.
Can you replace an anode rod yourself?
It’s doable for handy homeowners, but often harder than it sounds. The rod is screwed into the top of the tank and is usually very tight after years of heat; it typically takes a large socket and a breaker bar, and sometimes an impact tool. You have to shut off the water and heat source and relieve pressure first, and you need enough overhead clearance to pull the old rod out, or a flexible rod to fit the new one. Using too much force can damage the tank fitting, so many people leave it to a plumber.
Want it checked?
We can check your anode rod, replace it with the right type for your water, and flush the tank at the same visit. If the tank has already started rusting, we’ll tell you honestly whether it’s worth maintaining or time to replace.
Anode rods and the rest of your maintenance
Anode checks pair well with an annual flush; see how to flush a water heater. If your heater is making noise, start with why your water heater is making noise. And if you’re not sure how old your heater is, here’s how to find out.
Key takeaways
- The anode rod corrodes on purpose so your tank doesn’t.
- Check it every two to three years, more often with a water softener.
- Replace it when it’s heavily corroded or the core wire is exposed.
- Rotten-egg smelling hot water often means switching to an aluminum-zinc or powered anode.
- Never remove the anode rod to stop a smell; the tank needs it.
Frequently asked questions
How long does a water heater anode rod last?
It depends on water quality. Many last several years, but softened or very hard water can use them up faster. Checking every two to three years is a good habit.
What happens if you don’t replace the anode rod?
Once it’s used up, the tank itself starts to corrode from the inside, which leads to rusty water and eventually leaks.
Can a bad anode rod cause rotten-egg smell?
Yes. A magnesium rod can react with certain bacteria in the water to produce hydrogen sulfide. Switching to an aluminum-zinc or powered anode often solves it.
Does replacing the anode rod void my warranty?
Check your manufacturer’s terms. Replacing it with an approved type generally doesn’t, but removing it entirely can affect the tank’s protection and warranty.
Do tankless water heaters have anode rods?
Most tankless heaters don’t, because they don’t store water in a steel tank. They need descaling instead.
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