How to Replace an Anode Rod

The anode rod's hex head, where a socket grips it, is usually 1-1/16 inch on a standard residential water heater. A rod that has never been removed since the tank was installed is very often seized by mineral deposits and years of thread sealant, so a breaker bar for leverage, or an impact wrench where one is available, makes far more difference here than on almost any other water heater job. A basic socket and a short ratchet are frequently not enough to break a stuck rod loose without rounding the hex.

Beyond the socket and breaker bar or impact wrench, have new thread sealant rated for potable water on hand for the replacement rod, and a garden hose for the small amount of draining this job needs.

1. Turn off power to an electric tank at the breaker, or set a gas tank's control valve to pilot, and close the cold water supply valve.
2. Open a hot water tap briefly to relieve pressure in the tank.
3. Connect a hose to the tank's drain valve and drain 3 to 5 gallons, enough to drop the water level below the anode port at the top of the tank.
4. Locate the anode rod's hex head, either exposed at the top of the tank or, on some models, hidden under a plastic cap or combined with the hot water outlet fitting.
5. Fit a 1-1/16 inch socket onto the hex head and break it loose counterclockwise using a breaker bar or an impact wrench, since a corroded rod can require significant force to start turning.
6. Once loose, continue unthreading by hand and withdraw the rod. If the ceiling or joists overhead do not allow a full-length rod to clear, use a flexible or segmented replacement rod instead, which folds or hinges as it comes out.
7. Inspect the old rod: if more than about six inches of bare steel core wire is exposed, or the reactive metal coating is mostly gone, replace it.
8. Wrap the new rod's threads with pipe thread sealant rated for potable water, thread it in by hand, then snug it with the socket and breaker bar.
9. Close the drain valve, open the cold water supply valve fully, and open a hot tap until the stream runs steady with no air.
10. Restore power or return the gas control valve to its normal setting.

The clearest sign is visual: once more than about six inches of the rod's bare steel core wire shows through what should be a coating of reactive metal, the rod has done most of what it can do and is close to offering no further protection. A rod that has shrunk to a thin wire along most of its length, rather than one with a consistent coating remaining, is past due even if six inches has not been reached everywhere along it.

A rotten egg smell in hot water only, not cold, is a separate but related signal, often caused by a magnesium rod reacting with sulfate-reducing bacteria in the water rather than the rod being worn out. Switching to an aluminum-zinc rod frequently resolves that smell without giving up sacrificial protection.

A water heater installed in a low crawlspace, a shallow attic, or with ductwork directly overhead often does not have the vertical clearance a standard 3 to 4 foot rod needs to come straight out. Flexible rods, made of short segments linked so the rod bends as it withdraws, and segmented rods that separate into pieces, both exist specifically for this situation and thread into the same port as a standard rod.

Measure the actual clearance above the anode port before ordering a replacement, since a flexible rod bought unnecessarily costs more than a standard one for no benefit, while a standard rod bought where there is no room for it cannot be installed without first creating clearance another way.

Match the material to the water, not just the tank. A magnesium rod is the default; an aluminum-zinc rod is the fix for a sulfur smell.