Water Heater Anode Rod: What It Does and When to Check It
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The Short Answer: An anode rod is a metal rod screwed into the top of a steel tank that corrodes in place of the tank. Most are magnesium or aluminum. Manufacturers say to inspect it every one to two years, more often with softened water, and replace it when it’s mostly eaten away. Once it’s gone, the tank starts to corrode. Replacing it is a job for a plumber.
What it does
Rheem’s anode bulletin (opens in a new tab) explains that every glass-lined tank has some microscopic bare metal areas exposed to the water. The anode is more reactive than the steel, so the water attacks it instead. A. O. Smith’s 2023 gas manual (opens in a new tab) calls it “a sacrificial metal rod that helps avoid corrosion and premature failure (leaks) in the tank,” and adds that it is “a consumable item.” A. O. Smith’s manuals also warn: “Once the anode rod is depleted, the tank will start to corrode, eventually developing a leak.”
On many tanks the anode sits under a cap or plug on top of the heater. On others it’s combined with the hot water outlet fitting. Rheem’s bulletin notes that on some Rheem models, including its heat pump heaters, point-of-use heaters of 20 gallons or less and residential direct-vent heaters, the anode isn’t accessible.
Types of anode
| Type | Where you’ll find it | What the manufacturers say |
|---|---|---|
| Magnesium | Standard in most gas and electric tanks | Bradford White’s anode bulletin (opens in a new tab) calls it the material that best protects the steel tank |
| Aluminum or aluminum alloy | Offered as a replacement option | Bradford White says aluminum is the better choice where water is more conductive, such as softened water or low pH, because magnesium is used up faster there |
| Powered (electronic) | A. O. Smith Voltex heat pump models | A non-sacrificial anode. A. O. Smith’s Voltex manual (opens in a new tab) says it “should not need to be replaced under normal operating conditions,” but it works only while the heater has power, so the manual says to drain the tank if power will be off for an extended period |
Rheem uses its own R-Tech anode in electric tanks. Its bulletins don’t say what it’s made of.
How often to check it
| Manufacturer | Inspection interval | Who the manual assigns it to |
|---|---|---|
| Rheem gas and electric | Remove and inspect annually; replace when more than 6 inches of core wire shows | Listed in the owner’s routine maintenance |
| A. O. Smith (2023 gas manual) | After the first six months, then annually; more often with a water softener | Written to the owner, or “have a qualified person replace it” |
| A. O. Smith (older manual 315628) | After at most three years, then annually; annually with softened water | Written to the owner (replacement steps are in the manual) |
| Bradford White | Every 2 years; more often with softened or phosphate-treated water | A qualified service technician |
| State | At least annually after the warranty period | A qualified technician |
The Rheem manual (opens in a new tab) sets the replacement point: when more than 6 inches of core wire is exposed at either end of the rod. A. O. Smith’s older manual (opens in a new tab) adds two signs: most of the rod is thinner than 3/8 inch, or about a third or more of its length shows the bare support wire.
Softened water speeds it up. A. O. Smith says artificially softened water “is exceedingly corrosive,” and Bradford White says a softener may increase how fast the anode is used up.
Why we leave replacement to a plumber
The anode is screwed tightly into a tank under water pressure. Getting it out takes a 1-1/16-inch socket, on some A. O. Smith models it’s under foam insulation, and A. O. Smith notes the anode can be as long as 35 inches, which needs clearance above the heater. Bradford White and State assign the job to a qualified technician, and Bradford White’s heat pump manual (opens in a new tab) cites shock hazard and the risk of leaks. A plumber can also tell you whether a different material suits your water.
When to call one:
- The heater is past its first few years and nobody has checked the anode.
- You have a water softener.
- The hot water smells like rotten eggs. See hot water smells like rotten eggs.
- The hot water is rusty or discolored, which can mean the anode is gone and the tank itself is corroding.
Don’t remove it for good
Every manufacturer warns against running a tank without an anode. Rheem says doing so “will greatly shorten the life of the glass lined tank and will exclude warranty coverage.” A. O. Smith, Bradford White and State all say removing it voids the tank warranty. If the anode is causing an odor, the fix is a different anode type plus treating the tank, not taking it out.
RV water heaters
- Suburban tanks use a magnesium or aluminum anode that doubles as the drain plug. Suburban’s manual (opens in a new tab) has owners turn off the electric power, gas and water pump, open a hot and a cold faucet, then remove the anode with a 1-1/16-inch socket to drain the tank. Let the water cool first, since it may be hot. Suburban says to refill the tank and remove all air before relighting or switching the power back on, and recommends replacing the anode yearly, or when more than 75% is consumed. It says to use thread sealant approved for drinking water when reinstalling it, and warns against putting any non-Suburban accessory part, such as an add-on electric heating element, in the anode’s place. See Suburban SW6DE troubleshooting and Suburban RV water heater leaking.
- Atwood and Dometic tanks are aluminum and don’t use an anode. Dometic warns (opens in a new tab) that installing an aftermarket anode can damage the tank.
Frequently Asked Questions
Q: Can I tell if my anode is used up without removing it? A: Not reliably. Rusty hot water and a rotten-egg smell are clues, but the only way to judge the rod is to take it out and look, which is why the manuals give an inspection interval.
Q: Does replacing the anode make a water heater last longer? A: It can. State’s manual says replacing a depleted anode “can extend the life of your water heater,” and Suburban says regular replacement can greatly extend tank life. It won’t help a tank that is already leaking.
Q: Is the anode covered by warranty? A: No. A. O. Smith calls anodes a consumable item not covered under warranty, and Bradford White’s heat pump manual (opens in a new tab) says the inspection and replacement rod aren’t covered. Failing to replace a consumed anode can put the tank warranty at risk.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith: residential gas water heater manual 100366712 (Rev A, February 2023) (opens in a new tab)A. O. Smith residential gas tanks; what the anode does, inspection interval, warranty warning.
- A. O. Smith: residential gas water heaters instruction manual 315628-002 (opens in a new tab)A. O. Smith residential gas tanks; signs of a depleted anode, softened water, odor causes.
- A. O. Smith: Voltex hybrid heat pump Use & Care guide 318257-002 (opens in a new tab)A. O. Smith Voltex heat pump water heaters with a powered anode.
- Rheem: residential gas Use & Care manual AP23057 Rev 01 (opens in a new tab)Rheem residential gas tanks; annual anode inspection and replacement threshold.
- Bradford White: gas water heater installation and operation manual 238-51008-00 (opens in a new tab)Bradford White atmospheric gas tanks; anode inspection every 2 years by a qualified service technician.
- Bradford White: water heater anode rods (For The Pro bulletin 122) (opens in a new tab)Bradford White tanks; magnesium vs aluminum anodes and water chemistry. Written for professionals.
- Bradford White: hybrid electric heat pump water heater I&O manual 238-55123-00 (opens in a new tab)Bradford White heat pump tanks; anode inspection by a qualified servicer or plumber, warranty terms.
- State: residential gas instruction manual 184115-000 (opens in a new tab)State residential gas tanks; anode inspection by a qualified technician.
- Rheem technical service bulletin 1201: anode rods, cathodic protection and the porcelain lining (opens in a new tab)Rheem and Ruud tanks; how the anode protects the lining and which models have no accessible anode. Linked from rheem.com; served from a distributor document server.
- Suburban: tank water heaters operation and maintenance guide 206244 (Rev A, 2023) (opens in a new tab)Suburban RV tank water heaters; anode as drain plug, yearly replacement.
- Dometic: using after-market anode rods (opens in a new tab)Dometic and Atwood RV water heaters, which use aluminum tanks without an anode.
- A. O. Smith: model and manual lookup (opens in a new tab)Find the instructions for the model on your rating plate; this directory does not verify a particular error-code meaning.
- Rheem: owner help and support (opens in a new tab)Identify the applicable model instructions or contact Rheem support.
- Bradford White: find your water heater manual (opens in a new tab)Use the model and serial number to locate the correct documentation.
- Suburban: service and support (opens in a new tab)Identify the appliance behind the RV badge and obtain its operating instructions.
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