AO Smith water heater anode rod replacement takes a 1-1/16 inch socket on a hex-head rod that hangs into the tank from the top, according to A. O. Smith's maintenance guide. Shut off the gas or power and the cold supply, drain some water, swap the rod, and refill completely before restarting.
Figures checked September 2026. Prices are from parts listings loaded on 16 September 2026; inspection and warranty wording is quoted from the A. O. Smith documents under Sources.
| Part (A. O. Smith number) | Price, seller 1 | Price, seller 2 | Labor | Source |
|---|---|---|---|---|
| 100108660 magnesium rod, 3/4 in. NPT x 32 in. (replaces 9001829005) | $51.96 (Hotwaterparts.net) | $62.12 (FurnacePartSource) | Not included | Listings, Sep 2026 |
| 100109223 hex-head magnesium, 3/4 in. NPT x 44 in. | $89.95 (Hotwaterparts.net) | $82.38 (FurnacePartSource) | Not included | Listings, Sep 2026 |
| 100109594 hex-head aluminum, 3/4 in. NPT x 33 in. | $46.95 (Hotwaterparts.net) | $54.40 (Water Heater Distributors) | Not included | Listings, Sep 2026 |
| 100110784 flexible hex-head magnesium, 48 in. | $185.96 (Hotwaterparts.net) | One listing found | Not included | Listing, Sep 2026 |
| Plumber replacement, parts and labor | n/a | n/a | $125 to $300 (Fixr); $150 to $350 (HomeGuide) | Fixr and HomeGuide, Aug 2025 |
These part numbers show price spread, not fitment; A. O. Smith matches parts by serial number.
A. O. Smith fits a sacrificial anode made of aluminum, magnesium or zinc, and its ProLine literature says all its products use CoreGard stainless-steel core anode rods. A. O. Smith says the core lets the anode be secured in place. ProLine Master models add longer, larger or higher-current anodes, depending on model.
Those statements come from A. O. Smith's ProLine product page and its ProLine brochure AOSRB01013, copyright 2021, which describes the CoreGard core as unique to A. O. Smith.
For smelly water, the 2023 Use & Care Guide says the standard rod can be swapped for a special zinc anode that may reduce or remove the odor, and it tells owners to contact a qualified person for that change (A. O. Smith, Residential Gas Water Heater Use & Care Guide, July 2023).
On a standard A. O. Smith tank the anode hangs down into the water from the top of the heater. The maintenance guide says exactly that, and the 2015 residential gas manual labels the anode as its own item in the component drawing, separate from the hot water outlet. Look for a hex head on the tank top; forum answers ranking for this search describe it under a plastic cap.
The parts catalog shows why owners still get confused. Hotwaterparts.net's A. O. Smith anode listing on 16 September 2026 included nipple-style rods (for example 100112446, 3/4 inch NPT with a 4 inch nipple) alongside hex-head rods, so some models carry the anode on a pipe nipple instead. The repair parts illustration in your heater's manual shows which one you have.
A 1-1/16 inch socket. A. O. Smith states the size twice: its online maintenance guide says to use a 1-1/16 deep well socket on an electric impact wrench, and the 2023 Use & Care Guide says the anode rod requires a 1-1/16 inch socket.
A reply in the doityourself.com thread that ranks for this search advises having a long breaker bar ready for an old rod. If the tank rotates or the fitting flexes while you pull, stop; a twisted tank connection can start a leak.
A. O. Smith's current guide says to inspect the rod after the first six months of use and at least once a year after that. Its older residential gas manual allowed up to three years before the first check. Softened water shortens every schedule, because A. O. Smith says softening makes the rod deplete faster.
| A. O. Smith document | First check | Afterward | Softened water |
|---|---|---|---|
| Residential Gas Water Heaters manual 315628-002 (printed March 2015) | After three years at most | Annually | Annually from the start |
| Residential Gas Use & Care Guide 100362953 (printed July 2023) | After the first six months | At least annually | More often |
| hotwater.com maintenance guide (accessed Sep 2026) | Not stated | Once a year | Not stated |
The documents also define "worn out" differently. The 2015 manual lists two signs: most of the rod's diameter under 3/8 inch, or roughly a third or more of the support wire exposed. The maintenance guide says a healthy rod is smooth and about a half inch across, and that several inches of bare core wire means replace it. Follow the newest document for your model when they disagree.
Turn the heater off, close the cold supply, drain about 5 gallons, then unscrew the old rod and seal the new one's threads. That is the sequence in A. O. Smith's residential gas manual, which also says to purge air and check for leaks before restarting. The steps below combine it with the maintenance guide.
The 5-gallon drain figure and the sealant step come from the 2015 residential gas manual. The full-tank warning is A. O. Smith's: an electric element fired without water around it will be destroyed, per the maintenance guide.
Budget $125 to $350 for a plumber, based on Fixr's $125 to $300 and HomeGuide's $150 to $350 national ranges from August 2025, or $46.95 to $185.96 for the genuine A. O. Smith rods priced above. Neither cost guide is brand-specific, so the part price is where A. O. Smith owners see the difference.
HomeGuide's repair cost guide, updated 7 August 2025, assumes a $20 to $50 part. Several A. O. Smith rods sit inside that band, such as 100109594 at $46.95 on Hotwaterparts.net, but the longer magnesium and flexible rods do not: 100109223 was $82.38 at FurnacePartSource and the 48-inch flexible 100110784 was $185.96.
Fixr's water heater repair cost page, updated 29 August 2025, gives plumber labor at $50 to $150 an hour. For cross-brand cost context, read the water heater anode rod replacement cost guide.
No. A. O. Smith's residential limited warranty says anode rods are consumable maintenance parts and are excluded from warranty coverage. The 2023 Use & Care Guide repeats that rods are not covered, and adds that an anode must stay installed at all times or the warranty is void.
The same limited warranty, 100293072 Rev C, April 2018, sets these terms:
For error codes and other warranty questions on these heaters, see the AO Smith water heater repair guide.
Use the serial number. A. O. Smith's parts page asks for the heater's serial number to find the correct part, and says it will not be liable for a part recommendation made without one. The serial and model numbers are on the rating plate on the side of the tank.
Two details help at the counter. Part numbers change: FurnacePartSource lists 100108660 as the updated version of 9001829005, so an older manual may show a number that no longer sells. And clearance matters as much as fit; if there is not enough room above the heater, a flexible or segmented rod is the route the maintenance guide points to.
A. O. Smith's 2023 guide lists serious burns in about 30 seconds at 130°F and in under 5 seconds at 140°F (Use & Care Guide 100362953). Its maintenance guide says to turn the heater off a few hours before draining so the water cools, and to wear thick gloves and goggles.
| Situation | A. O. Smith guidance | Next step |
|---|---|---|
| Rod worn to its core, tank sound | Replace the rod; it is a consumable part | Buy by serial number |
| Rotten-egg smell in hot water only | Special zinc rod may help; bacteria is the cause | Zinc rod, then chlorination by a pro |
| Water leaking from the tank body | A depleted rod lets the tank corrode and leak | See repairing a leaking water heater |
| Leak on an out-of-warranty tank | Owner pays labor under warranty 100293072 | Compare water heater repair prices with a new unit |
| Other faults, codes or no heat | Outside anode service | Start at the water heater problems hub |
Yes. The 2015 residential gas manual says each heater contains at least one anode rod, and the 2023 guide says one must be installed at all times.
Not by A. O. Smith's instructions. The residential gas manual calls for draining about 5 gallons after shutting off the cold supply and relieving pressure.
No. A. O. Smith warns that removing the anode leaves the tank unprotected and voids the tank warranty. Ask about a special zinc rod instead.
A. O. Smith's residential gas manual says that once the rod is depleted the tank starts to corrode and eventually leaks. The rod is a far smaller purchase than a heater, so replacement makes sense while the tank is still dry.
Yes. A. O. Smith's hybrid manual says the control shows error code 044 when the rod is depleted, and reaching it means removing the jacket cover and a 10 mm wire nut first.
Independent Research
Published ranges for tank, tankless and heat pump replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
