Water Heater Anode Rod Replacement

What a water heater anode rod does

A steel tank would rust through quickly on its own. The anode rod is a metal rod, usually magnesium or aluminum, that screws into the top of the tank and corrodes instead of the tank. It’s sacrificial: once it’s gone, the tank starts to corrode. Some heaters have a “combo” anode built into the hot-water outlet fitting rather than a separate hex plug.

When to replace the anode rod

• On a schedule: inspect every 2–3 years, or every year with softened water.
• When it’s worn: the steel core wire is visible, or the rod is pitted down to less than about half its original thickness.
• For smelly water: hot water smells like rotten eggs (sulfur) but the cold doesn’t.
• For rusty or discolored hot water: this can also mean the tank is corroding. Check the anode before it’s too late.

If the tank is already leaking from the body, a new anode won’t help. See water heater replacement costs instead.

Choosing the right anode rod

Match the length and thread to your tank. Most US residential heaters use a 3/4" NPT thread. Your model number lets the manufacturer or a supply house confirm the right part.

How to replace a water heater anode rod

1. Turn off the heat. Gas: set the control to “Pilot” or “Vacation.” Electric: switch off the breaker.
2. Shut the cold-water supply at the valve above the heater. Open a hot tap in the house to relieve pressure.
3. Drain a few gallons. Attach a hose to the drain valve and drain about 3–5 gallons, so the water level is below the anode fitting.
4. Find the anode. It’s a hex head on top of the tank, sometimes under a plastic cap or insulation. If there isn’t one, it’s probably a combo anode in the hot outlet.
5. Break it loose. Turn counter-clockwise with a socket and breaker bar. Factory anodes are tight, so a short burst from an impact wrench works best. Don’t rock the tank, because that strains the pipes.
6. Pull the old rod and compare it to the new one.
7. Install the new rod. Wrap the threads with 3–4 turns of PTFE tape, thread it in by hand, then snug it firmly.
8. Refill and check. Close the drain, open the cold supply, and let air bleed out of the open hot tap. Check for leaks, then restore gas or power.

Tip: while the tank is partly drained, it’s a good time to flush sediment.

When to call a pro instead

• The anode won’t budge, even with an impact wrench.
• There’s less than about a foot of clearance and no room for a flexible rod.
• The anode is a combo type in the hot outlet, which means disconnecting the water line.
• The rod is completely gone. The tank may already be corroding, and a pro can tell you if it’s worth saving.

A fair price for a pro anode replacement is about $275, including the rod, a sediment flush and a leak test.