Water Heater Anode Rod Replacement
Water heater anode rod replacement on most tank heaters comes down to this: turn off the heat and cold supply, drain a few gallons, unscrew the old rod from the top of the tank with a 1-1/16-inch socket, and thread in a new one. HomeGuide puts the part at $20 to $50, or $150 to $350 if a plumber does it.
The hard part is usually getting the old rod to let go. Factory anodes are installed tight and then sit for years in hot water.
What an anode rod does
The anode rod is a metal rod that hangs inside the tank and corrodes on purpose. Water attacks the more reactive metal first, so the rod wears away instead of the steel tank. Once it's gone, the tank starts to rust from the inside.
Both gas and electric tank heaters use one. Most tankless heaters don't, because their heat exchangers aren't glass-lined steel. Corro-Protec notes its powered anode doesn't work with tankless, stainless steel or plastic-lined units.
When to check and replace it
Sources differ on timing, but they all say check it more often than most people do:
| Guidance | Interval |
|---|---|
| A.O. Smith troubleshooting guide | Inspect and replace every year or as needed |
| HomeGuide, citing plumbers | Replace every 3 to 5 years |
| Corro-Protec, typical rod life | 2 to 5 years, depending on water and use |
Hard water and water softeners both use up anodes faster. If you have a softener, check the rod at least as often as the manual suggests.
Signs the rod is failing, according to Corro-Protec:
- Rusty-colored hot water
- A sulfur or rotten-egg smell from the hot taps only
- Popping or hissing from the tank
When you pull it, replace it if you can see the steel core wire, if it's eaten down unevenly to a thin stub, or if it's caked in heavy scale. A healthy rod looks like a rough metal bar, not a coat hanger.
Choosing a replacement
| Type | Best for |
|---|---|
| Magnesium | Softer water |
| Aluminum | Harder water |
| Powered (impressed current) | Persistent rotten-egg smell |
Most replacement rods use a standard 3/4-inch NPT thread. Measure the old rod's length, or look up your heater's model number, before you buy.
A rotten-egg smell in the hot water is often bacteria reacting with the anode. A.O. Smith's troubleshooting guide describes raising the water temperature to 140°F for a short period to kill the bacteria, then returning it to a safer setting. That water scalds, so warn everyone in the house. Corro-Protec says a powered anode, which replaces the sacrificial rod and plugs into an outlet, can solve the smell.
If there's little headroom above the heater, buy a segmented or flexible "link" anode. It bends as it goes in, so you don't need a full rod's length of clearance.
Tools and parts
- New anode rod and thread sealant rated for potable water
- 1-1/16-inch socket for most factory rods
- A breaker bar or long-handled ratchet
- Garden hose and bucket for draining
- Gloves and goggles
- A helper, or a pipe wrench on the tank's top fitting, to keep the tank from twisting
Step-by-step replacement
Shut off the heat
Gas: turn the control to OFF. Electric: switch off the breaker.
Close the cold water supply
to the heater.
Relieve pressure
Open a hot water tap somewhere in the house.
Drain a few gallons
Attach a hose to the drain valve and let some water out, enough that the level drops below the top of the tank.
Find the anode
It's usually on top of the tank under a cap or plastic cover. On Bradford White heaters it's built into the hot water outlet fitting instead, which takes a different removal method.
Break it loose
Put the socket on the hex head and pull with a breaker bar. Corrosion and sediment make it tight. Steady force works better than jerking, and a helper bracing the tank keeps it from rotating.
Pull out the old rod
and inspect it.
Install the new rod
Wrap the threads with sealant, slide it in, and tighten it firmly without overtightening, which can damage the tank.
Refill
Close the drain valve, open the cold supply with a hot tap open, and run the tap until it flows steadily with no air.
Check for leaks
at the anode fitting, then restore gas or power.
Mistakes to avoid
- Using an impact wrench on a stuck rod. It can damage the tank fitting. If a breaker bar won't do it, call a plumber.
- Draining the whole tank. You only need the water below the top.
- Overtightening the new rod.
- Powering an electric heater before it's refilled.
- Buying a rod by guesswork. Check the model number or measure the old one.
When to hire a plumber
Call one if the rod won't budge, if the top of the tank has no clearance, or if the heater is old enough that it isn't worth the effort. A tank past its expected life with a dead anode is usually a replacement candidate; see how long water heaters last.
FAQ
How do you replace a water heater anode rod?
Shut off the heat and cold supply, open a hot tap, drain a few gallons, and remove the old rod with a socket. Most factory rods take a 1-1/16-inch socket. Thread in the new rod with sealant, refill, check for leaks and restore power.
Do gas water heaters have an anode rod?
Yes. Gas and electric tank heaters both use an anode rod to protect the steel tank. On most models it's on top of the tank.
Do all water heaters have an anode rod?
Tank heaters with glass-lined steel tanks do. Most tankless heaters don't. Some tanks have the anode combined with the hot outlet fitting, so you may not see a separate hex head on top.
What size anode rod do I need?
Most rods use a standard 3/4-inch NPT thread. Length varies by tank size, so match the old rod or check your heater's model number.
Sources
- Corro-ProtecWater Heater Anode Rod Replacement: Step-by-Step Guide (opens in a new tab)
- A. O. SmithWater Heater Not Working? Troubleshooting Guide (opens in a new tab)
- HomeGuideWater Heater Repair Cost (opens in a new tab)
- A. O. SmithHow to Drain and Flush a Water Heater (opens in a new tab)