water heating · guide · TN LLP #5045
The Anode Rod, and Why Your Tank Rusted Out
The sacrificial part almost nobody checks, and what happens when it is spent.
Short answer
The anode rod is a sacrificial metal rod inside the tank that corrodes so the steel does not. It is consumable. When it is gone and nobody replaced it, the tank itself starts rusting — which is why so many heaters fail from the inside out.
Almost nobody outside the trade knows this part exists, and it is the single component that most determines how long a tank heater lasts. It is also cheap and replaceable, which makes the general ignorance of it genuinely costly.
How it works
A steel tank full of hot water is an ideal environment for corrosion. The anode is made of a metal that corrodes more readily than steel, so the chemistry attacks it first. As long as there is anode left, the tank is protected.
It gets consumed doing that job. Depending on water chemistry and use, a rod can be largely gone in a handful of years — sooner in hard or aggressive water.
What happens when it is spent
The protection stops and the tank begins corroding from the inside. You will not see it. The first sign is usually rusty water, and the second is a leak from the tank body, which is the point at which the heater is finished.
That is the failure mode behind most "the tank just went" calls. It did not just go. It had been going for a while with nothing left protecting it.
What to do about it
Have it checked every few years, and replaced when it is depleted. It is a modest job on a tank you plan to keep, and it is the cheapest life extension available for a water heater.
If the water is hard, treating it slows the whole process down, because aggressive water consumes the rod faster as well as scaling the tank.
Permits
Some plumbing work requires a permit and an inspection, and some does not. Whether one is required for your job is determined by the Authority Having Jurisdiction — the city or county building and codes office for your address — and it is at their discretion.
Usually requires a permit
- Water heater replacement and tankless conversion
- Whole-house repiping
- Water service line and sewer line replacement
- Gas line installation and repair
- Relocating a fixture to a new position
Usually does not
- Drain cleaning and clearing blockages
- Emergency and repair work
- Like-for-like fixture replacement
- Water heater repair
- Camera inspection and diagnostics
This is general guidance rather than a ruling, and it can differ from one town to the next. The Authority Having Jurisdiction makes the determination. Across the Bradley–McMinn corridor we pull the permit and book the inspection ourselves. Inside Hamilton County and Chattanooga the permit office does not accept an application from our license class, so permit-required jobs there are referred to a licensed partner who does the work and meets the inspector.
Common questions
The Anode Rod, and Why Your Tank Rusted Out — questions
How do I know if mine needs replacing?
Is it worth doing on an older heater?
My hot water smells like rotten eggs. Is that the rod?
Will I know the price before you start?
Are you licensed?
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