Anode Cathode? Anode Rod Replacement & Maintenance


Anode Definition and The Importance of the Anode rod, throughout history we have constantly been inventing new and better ways of doing things. These new inventions are often geared towards letting the human race live more comfortable lives. One such invention is the electronic water heater. Without it, people who live in cold climates would still be heating water up on a stove and manually transferring the heated water to a tub so they can bathe.

The invention of the electronic water heater means that people have access to hot water right off the tap with just the flick of their wrists. However, it is necessary to note that one of the most important elements that keeps a water heater functioning properly is the anode. Without it, the water heater would be useless.
Contents of this article

Anodes And What Are They

In order to obtain a good understanding of what a water heater anode is, it is best to first take a peek on the context within which it is normally used. This refers particularly to the movement of ions in an electric current. As every 5th-grader knows, the route that electrical currents take is normally in accordance with the direction towards which the positively charged ions are flowing. This route or direction in the flow of currents is known as anode. The negatively charged electrodes often flow in the opposite direction as the positively charged ones. This opposing current is referred to as cathode. It should be noted that the anode and cathode always go together regardless of where it is applied.

Galvanic cell with no cation flow

Galvanic cell with no cation flow

When the battery cell that houses the cathode anode are connected to an external source, the functions of each electrode can be defined as follows:

  • Anode + negatively-charged ions (anions) – this means that it attracts the anions and absorbs these into the battery cell. These anions would then flow through the cell to be expelled at the cathode.
  • Cathode + positively charged ions (cations) – this means that the cathode attracts the cations and absorbs these into the battery cell. These cations flow in the opposite direction of the anions and would then be expelled at the anode.

This anode cathode working relationship is a necessary part of ensuring that battery cells function correctly.

The anode can also function as positive or negative terminal depending on the type of battery cell. There are two main types of cells below are the types:

  • Galvanic cells– these are battery cells that draw electrical energy from the electrochemical reactions that are happening within the cell. In galvanic cells, the anode functions as the negative terminal through which the current passes on its way into the cell.
  • Electrolytic cells – these are cells that receive the electrical energy from an external source. The anode functions as a positive terminal in these cells.

Electrodes are not only beneficial for use in battery-related operations. As previously mentioned, it is also one of the most basic components of electronic water heaters.

Understanding the Function of the Water Heater Anode Rod

There are many different types of water heaters that are sold on the market today. However, despite all the differences in size, shape and style, these water heaters still contain the same basic components. These components include:

  • Tank – Most water heaters have tanks for storing water on. The inner portion of these tanks is lined with metal sheets that are often covered with a layer of fine glass. A layer of insulating material is usually added over the glass layer to ensure that the hot water inside the tank remains hot for as long as possible.
  • Thermostat – This is the apparatus that controls the water temperature inside the tank. Most thermostats are designed to automatically go on or off depending on the temperature of the stored water.
  • Shut off valve – This component is located outside the water heater and is separate from all the other components. It serves as a stopper that shuts the water supply going into the tank. In most cases, the valve shuts off the water supply on all the pipes throughout the house. This is often located at a distance from the water heater, often at a separate room in the house. It’s important know the exact location of the shut-off valve encase of emergencies. This is because the first step in doing any maintenance work on the pipes or the water heater involves shutting off the water supply.
  • Gas Burner – This is normally found on water heaters that make use of gas for heating the water supply. The burner has a separate shut-off valve that turns off the supply of gas that goes to the burner. The location of this valve also has to be noted by homeowners since they would also have to shut it off before doing any kind of work on the water heater. Other types of water heaters, such as the electronic ones, have its own power shut-off mechanism that controls the flow of energy onto the heater. It is important for every one to know where their water heaters are getting its energy supply from and how to turn these on and off. This is a basic safety precaution required when troubleshooting any possible issues with the heater.

Aside from these main components, there is also one more important component that every water heater needs. This component is known as the anode rod. It is referred to as ‘Sacrificial Anode Rod’ because the anode rod purpose is to keep rust and corrosion away from the tank’s inner metal lining. The rod plays a vital role and it is often made of metals such as aluminum or magnesium anode rod. There are also several newer versions that contain anodes made out of a combination of zinc and aluminum, though these are mostly used in ship tanks. A homeowner can tell which part is the rod by looking for a rod that slightly protrudes from the base of the tank.

How the Water Heater Anode Rod Works

In order to properly understand the role that an anode rod plays in preventing a water heater’s tank from corroding, it is best to first take a look at the electrochemical process involved in corrosion. This can be started with the elements that make up each of the components that are involved in the process of corrosion, such as:

  • Rust – rust is made up of the elements Iron (Fe) and Oxygen (O). To be more specific, the chemical formula for rust is Fe2O3, also known as Iron Oxide.
  • Water – water is made up of two basic elements: Hydrogen and Oxygen, hence the universally known chemical formula H2O.

In its basic form as H2O, water acts as an electrolyte that forms an electrochemical reaction with iron (Fe). Note that iron in itself is a chemical compound that binds quite easily with oxygen. Everyone knows that iron is the basic component of most metal alloys. Once the metal comes into contact with water, the iron readily absorbs the oxygen to form iron oxide or rust.

One reason why these rods are made of aluminum, magnesium, or zinc is because these metals are highly reactive as compared to other types of metals. Once the metal is dissolved in water, it releases electrons. The absence of these electrons in the iron is supplemented by the absorption of the water’s oxygen content. This would then become a continuous cycle wherein the oxygen absorbed into the metal would then facilitate the release of more electrons, which would then promote the absorption of more oxygen. This goes on until the rod becomes completely corroded.

The electrons released from the rod do not stay long in the water since these are absorbed by a cathode. Some water heaters have separate cathodes that are located a few inches away from the anode rod. In this case, it is often made of a different metal that is not as reactive to electrolytes as the metal used on the rod. However, there are also certain types of water heaters whose cathodes are incorporated into the main body of the anode rod.

Water heaters for home use are often equipped with anode rods that can last for up to 5-6 years. Homeowners would usually know when the rod would have to be replaced by simply looking at the length of the heater’s warranty. This is because the rod is often the first thing that expires among the heater’s various components. This is why once the heater reaches its 5th or 6th year of use, homeowners would have to be alert for any signs that the rod is failing.

Some signs to look out for

  • The water has an orange or reddish tinge.
  • The hot water released emits a sulfuric odor. One way of making sure that the odor does not originate from a different source is by checking the water supply in other parts of the house. Check the cold water flow as well to determine whether it also has the same sulfuric smell as the hot water supply.
  • The presence of debris such as flakes of rust every time the hot water tap is turned on.
  • If the hot water supply is significantly lower than normal. This is often caused by debris from the corroded parts of the tank blocking the pipes through which the hot water supply flows.

If these signs are present, then it means that the water heater’s anode rod might have to be replaced. In some cases, it may already be too late, especially if there is already a high volume of debris in the hot water. This is because the debris means that the water tank has already started to corrode, and in some cases, there might already be a leak on the tank. This means that the tank or the entire water heater system would then have to be replaced one of many reasons why the rod is malfunctioning and always checking will help hold a longer life unit.

water heater anode rod

water heater anode rod

Water Heater Anode Rod Replacement and Maintenance

The reason why water heaters come with a specific warranty period is because manufacturers are fully aware of the short rod’s life span. This means that once the time comes for you to call a technician to check on the water heater, it could already be too late. This is why homeowners are advised to replace the anode rod even before the warranty expires. This would ensure that the rod is still functioning correctly and corrosion has not started on any part of the tank yet. We have a great section on detailed water heater maintenance and replacements with easy to follow instructions.

Follow the steps below when replacing the Anode rod:

  • As previously mentioned, turn off the valves that supply both water and energy to the water heater. Working with the valves still on could cause extensive damage to various parts of the heater. It could also cause damage to people as well through accidental electrocutions or getting accidentally burned.
  • Drain the tank of its remaining water supply. Note that the water would still be hot so exercise caution while draining. It is best to drain this on a faucet that is located in a different room. The faucet should then be left on so that, once the hot water is drained, any remaining pressure within the tank would also be relieved.
  • Check if there is enough vertical clearance when removing the rod from above. Most water heaters have tanks that are about 3 too 4 feet in height. This means that the anode rod would also be that long. If there isn’t enough space between the top of the tank and the ceiling, then it would have to be tilted so that the rod can be removed. Be sure to disconnect all pipes from the tank first before tilting it. Also, it is best if the rod is loosened even before the tank is tilted to make the work go faster.

Note that the rod is normally fastened on the tank through a hexagonal head that is securely screwed onto a part of the tank’s top plate covering. In some cases, rust and corrosion might already have developed around the hexagonal head of the rod due to its constant exposure to moisture. This could add to the head’s tight fit. Most experts suggest applying a coat of lubricant on the hexagonal head prior to prying it loose. The lubricant would ensure that the head can easily be turned clockwise.

Once the lubricant has been given enough time to penetrate into the inner recesses of the hex head, wrench it loose with use of special tools such as an impact or a socket wrench. The difference in the type of wrench to use for unscrewing the hex head depends on whether the head is protruding over the top of the water heater’s tank or if it is recessed onto the main plate of the tank head. Never attempt to wrench the hex head loose with your bare hands. It is usually impossible to unscrew the head manually, the friction caused by handling the head could also cause injury to the hands especially when the head is still warm.

As soon as the head is unscrewed, simply pull out the anode rod. This step can easily be accomplished since the rod is normally not attached to any other component on the tank. Also, while on the process of unscrewing the hex head, be on the lookout for any water that might leak out of the opening created by the separation of the head from the tank. If there is some leakage, drain more water off of the tank before completely removing the anode rod. As previously mentioned, bend or tilt the tank a little to the side if there is insufficient overhead space for completely removing the rod out of the tank.

How to Replace the Anode Rod in your Hot Water Heater ( Video )

When replacing the water heater anode rod, it is important to take note of what type of metal was used for the current rod. It is not advisable to replace it with a different type of rod since this might not be compatible with the rest of the tank’s components. This means that if the original rod is made of magnesium, then replace it with a magnesium rod as well. However, since most metals can look the same to the untrained eye, it could be difficult to tell whether the rod is magnesium, zinc, aluminum, or a combination of zinc and aluminum.

One way of differentiating by checking on the top of the rod’s hex heads. Remember that magnesium rods always have a bump on its hex head, while aluminum rod hex heads are completely flat. If  unsure, bring the rod to a store so that the experts can verify what type of rod it is and provide the correct replacement.

When these maintenance steps on the anode rod are done at least once every 5 years, homeowners can rest assured that their water heaters would last for more than the manufacturer’s warranty says it would.

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