The Water Heater Part Nobody Checks

Inside a tank water heater there is a metal rod hanging down into the water. It is called a sacrificial anode, and its entire job is to corrode so that the steel tank does not.

When the rod is used up, the corrosion moves to the tank. Then the tank leaks, and a leaking tank is not repairable.

How it works

A steel tank sitting full of water will corrode. The anode rod is made of a metal that corrodes preferentially, so the electrochemical process attacks the rod instead of the tank walls.

It is genuinely sacrificial. It is supposed to be consumed. The failure is not that it corrodes, it is that nobody replaces it once it has.

Why it matters more in North Texas

Our water is hard, and hard water is harder on a tank. Combine that with sediment building on the tank floor — which insulates the burner from the water and forces it to run hotter — and the conditions inside the tank are more aggressive than they would be in a soft-water area.

Our guide on hard water in North Texas covers the wider effects, and the one on flushing a water heater covers the sediment side.

How long a rod lasts

It varies with water chemistry, water usage and the type of rod. In hard water with heavy use it is consumed faster than in a soft-water house with two occupants.

The practical point is that on a tank that is several years old and has never been inspected, the rod is quite possibly gone — and every month after that is the tank itself corroding.

How it gets checked

The rod threads into the top of the tank, usually under a cover or a plastic cap. Checking it means shutting off the water and the fuel or power, draining down a little, and removing the rod to inspect it.

If it is heavily corroded, thin, or largely gone with the core wire exposed, it needs replacing.

Two practical complications: the rod is often torqued down hard from the factory and can be difficult to remove, and some installations do not leave enough overhead clearance to withdraw a full-length rod. A segmented rod solves the clearance problem.

When it is worth doing

• On a tank in its early years, replacing a spent rod is straightforwardly worth it — it buys you tank life for a small part cost.
• On a tank that is already near the end of its expected life, the money is usually better put toward replacement.
• If the tank is already leaking, it is too late. A leaking tank is replaced, not repaired.
• If you have a water softener, note that softened water can consume some rod types faster — worth mentioning when the rod is specified.

The rest of the maintenance

Anode inspection sits alongside two other things worth doing on a tank heater:

1. Flushing the sediment out of the bottom of the tank. In hard water this matters and it is the noisy-tank cause.
2. Testing the temperature and pressure relief valve, which is a safety device.
3. Checking the expansion tank, if the system has one — our guide on expansion tanks covers why they matter.

If your heater is getting on

Knowing the install date is the single most useful thing. If it is past its expected life and has never had maintenance, plan the replacement rather than waiting for the flood. Call (469) 338-5533 and we will tell you honestly where yours is.