A water heater anode is used in most hot water tanks in order to prevent the corrosion of the tank's metal lining. As long as the anode in the system is working, the metal of the rod wears away rather than the hot water heater lining. Anode rods are usually found near the outlet pipes on the inside of the heating tank and are connected with a hex head screw.
Rods used in water heater tanks can be nearly 4 feet long, so they are quite large and heavy. If anything goes wrong with the anode in your heating system, it is usually a job for the plumber, but knowing the sort of problems that affect water heater anode rods can help you to save money by catching them before they inhibit the functioning of the meter.
The anode rods are designed to draw corrosion away from the tank, and into the rod itself. For this reason, the most common problem with water heater anode devices is corrosion of the metal rod. You can see the damage on aluminum rods, which are commonly used in hard water areas, by examining the anode, and looking for the steel wire of the core.
If this is exposed, or there is passivisation of the rod. Anode rod corrosion is predictable, starting at the very top or bottom of the rod, and progressing into the core, which is made of steel wire. Anything more than around 6 inches of corrosion down to the wire indicates that the wire should be replaced.
2. Calcium Carbonate Build-up
Often, when anodes are removed from hot water tanks, they are covered in a white mineral. This is calcium carbonate, and often can be removed by brushing it down with a towel. Calcium carbonate can sometimes form a hard layer on the surface of the anode. While this will serve to protect the rod from corrosion, it may have a detrimental effect upon the surrounding tank.
Brush calcium carbonate away. This form of calcium carbonate build-up is called passivization, as it converts the rod from active (attracting corrosion) to passive (repelling corrosion). If the rod becomes corrupted by passivization, the rod will flake where it is bent. It may also become heavily pitted.
3. Soft Water
The use of softening agents in water, such as phosphates and rock salt, can cause corrosion to speed up, so that the corrosion can occur nearly three times as quickly as in hard water. This corrosion will race through the anode, corroding not only the soft, sacrificial metal, but also the steel wire.
Once the anode has been destroyed like this, the hex head of the tank will become damaged, followed by the tank itself. If you find the anode is reduced by more than 1/2 of the original diameter of the rod, then it will need to be replaced. If the anode becomes too damaged, it may fall away to the bottom of the tank (if the corrosion occurs at the top first). This can cause aluminum to mix with the hot water.