August 4, 2009
The anode rod is the water heater’s defense mechanism against rust and corrosion. Most water heaters use a “sacrificial anode rod” designed to deteriorate by attracting oxidants away from the tank. Some water heaters use a chemically inert anode rod to which electrical power is provided to achieve the same anti-corrosion function. If equipped with such, the information presented below does not pertain.
The anode rod is made of magnesium or aluminum wrapped around a steel core. The magnesium or aluminum covering has a higher galvanic reactivity than the steel core. This means that the magnesium or aluminum will corrode at a higher rate than the steel.
Dissimilar metal corrosion, often referred to as “electrolysis”, is a condition that occurs when metals of dissimilar composition are joined and come into contact with an electrolyte. Water is a weak electrolyte. Hence, when two dissimilar metals are joined and come into contact with water (or other electrolytes), corrosion occurs at an accelerated rate. The “less noble” metal, or metal with higher reactivity, will corrode before the other.
Corrosion occurs when the metal with the lesser galvanic reactivity (more noble) attracts ions from the less noble metal. This chemical reaction produces electrical current in the same manner as an automotive battery. However, the current created in the water heater is negligible.
The rate of the anode’s deterioration depends upon the quality of the water. Water with high mineral content or water treated with a water softener will increase the rate of deterioration.
How often should the anode rod be inspected?
Water heater manufacturers specify different inspection intervals. However, AAA AUGER recommends inspection every 5 years (unless directed more frequently by the manufacturer).
Typically, the magnesium or aluminum covering will start corroding at the bottom of the anode rod. If any part of the core is exposed or the exterior is pitted, the anode rod should be replaced.
Anode Rod Replacement
Items Needed :
- Eye protection
- Protective gloves
- Breaker box lock out kit (for electric water heaters without a readily accessible cut-off switch)
- Quality garden hose capable of withstanding high water temperatures
- #2 Flathead Screwdriver
- Channel-lock pliers
- Thread sealant – heat tolerant
- Wire brush
Replacing the anode rod isn’t complicated. However, there may be some obstacles that hinder the process. Many heaters are installed in confined areas offering little work room. This may require the removal of the heater. The instructions below do not detail the removal or installation of the water heater.
(1) Refer to the Flushing Procedure and follow the instructions through step 2.
(2) In the closest bathroom, turn the hot water on completely at the bath tub faucet. This will depressurize the system.
(3) Once depressurized, remove the anode rod by unscrewing it from the top of the tank. On most heaters, the anode rod is threaded in the water heater on top. The word “anode” is usually embossed in the steel jacket next to the hex-nut used for its removal.
(4) Once removed, clean the female threads in the tank with a wire brush.
(5) Apply a light coat of thread sealant to the male threads on the new anode rod and install in the heater.
Note : If you decide against replacement of the anode rod, NEVER attempt to clean it with detergents or acid based cleaners as this could be dangerous and cause damage to the anode rod.
(6) Continue with steps 3-14 in the Flushing Procedure.