If you’re asking yourself questions like, “Are anode rods universal? Where are dip tubes? How do I troubleshoot an expansion tank?” then you’re on the right track for learning the maintenance of a water heater.
One of the first things you’ll learn during plumbing training is that maintenance on water heaters is vital to preventing breakdowns and prolonging the life of the equipment. Some maintenance items are obvious: periodically drain the tank, inspect for any leaks, exercise the relief valve and keep the vent termination outside clear. With that said, there are other hidden maintenance items that, if neglected, can cause tank failure.
Anode Rod Maintenance
The anode rod is a device that serves only one purpose, to extend the life of the tank. The tank is the only part of the water heater that cannot be replaced. If the tank fails, you replace the entire unit. The anode is a “sacrificial” part, meaning the electrochemical activity that destroys your tank, will instead, attack the anode rod. Anode rods don’t last forever. They become corroded, and when the anode material completely dissolves, there is nothing left to protect the tank.
Components of an Anode Rod
Most of the anode rods sold today are made of zinc, aluminum or a combination of both. This material is most effective for protecting the heater and is less likely to cause odors in hot water.
All anode rods are made to fit in a ¾” NPT socket. Some replacement rods might only come in one length, but if it’s too long, you can cut some off. You won’t hurt it a bit.
If you are working on a newer water heater or one that’s 20 years old, the procedure is no different. Water heater manufacturers have found ways to make tanks in less time and use less material, but their basic construction is the same. Maintaining the anode rod is a critical step in extending the life of any tank.
Locating the Anode
Some anodes are threaded into the top of the tank with a large, visible hex head, while others are hidden under a knockout plug stamped into the outer jacket. A third possible option, is where a manufacturer provides an anode that is an extension of the steel pipe nipple on the hot water outlet of the heater. You would never find this if you didn’t already know it was there. The advantage of this is they are fairly easy to remove and inspect, as long as you have an 18” pipe wrench and strong biceps.
The hex-type anode might be easier to find, but it’s usually much more of a challenge to remove for inspection. I recommend a ½” drive, 1 1/16” socket and a breaker bar. Once you get a hold of it, it will require some might to free it from its lifelong grip on the threads of the tank. Upon removal, you observe whether or not the rod is intact. Depending on the quality of the water, it may be covered with a clear, slimy residue, which easily rinses off. If you see that its best days were in the past, replace it.
Dip Tube Maintenance
Another hidden component on every tank-type water heater is the dip tube. This secret gem is also out of sight, inside the tank. As you might guess, it’s really important. The dip tube is an extension of the cold water inlet that prevents the incoming water from mixing with the hot water in the tank by directing it to the bottom, where the burner is.
All water heaters experience a stratification of temperatures, with the hotter, more buoyant water at the top of the tank, and the cooler, heavier water at the bottom. If the dip tube is cracked or broken, the cool water coming into the tank mixes with the hot water at the top. What happens after that is enough to confuse any user into thinking the hot and cold on the faucets might be switched or worse yet, that they need a new water heater.
Repairing a Dip Tube
A dip tube is a very inexpensive plastic tube that can cause a lot of trouble if it isn’t working. To replace it, you remove the cold water supply nipple and dig out what is left of the old one with a flat screwdriver. If it’s broken off completely, let it stay in there forever, drop a new one in its place and life will return to normal again.
Expansion Tank Maintenance
The last hidden maintenance trick is diagnosing an expansion tank. Unlike boilers, not all potable water heating systems will require an expansion tank. Since it’s what we call an “open” system, it does not build up pressure in the same way when the water is heated. When the pressure in the system increases, any user can open a faucet and relieve that pressure. Systems that require a thermal expansion tank are rare.
If you find a system that has one, they really do need it, so it’s a good idea to check the tank and make sure it’s working properly.
Expansion Tank Troubleshooting
There is an easy way to tell if the tank has failed, you just have to have the right touch. An expansion tank is half water and half air. Both halves are divided by a diaphragm. If the diaphragm ruptures, the tank fills with water. When you tap on the side of the tank with your fingernail, or a screwdriver in case you’ve chewed them off, (not recommended for plumbers) you will hear a hollow pinging noise on the airside and a low thud on the waterside. If both sides thud, your diaphragm has failed and needs to be replaced.
If you pass the “ping” test you can take one more step to ensure the air pressure in the tank is correct. Most tanks come pre-charged to 40 psi, and this is great for most systems. If you test it and it’s less than 40 psi, some of the air has leaked out, maybe because the Schrader valve is loose or maybe someone keeps messing with it.
Testing the pressure is easy to do, but first, you must turn off the water and drain down the system to at least below the level of the expansion tank. If you try to read the pressure while the water is still on, you are reading the water pressure in the system, not the air pressure in the tank. If it’s less than 40 psi, pump it up and tighten up the Schrader valve and the cap that covers it. Refill the system and you are good to go.
Do you already how to install a gas water heater? Do you want to know more about the different components of a water heater, their functions and how to maintain them? If so, check out SkillMill’s™ Introduction to Water Heaters course.
Interplay Learning Plumbing & HVAC Expert
Frank is Interplay’s resident plumbing and HVAC expert. While he began his career in the plumbing trade, his passion for HVAC led him to become an Associate Professor and HVAC Program Chair, at Ivy Tech Community College. Frank is a Licensed Mechanical, Plumbing and Electrical Contractor, and owns his own mechanical services company. As an educator, Frank is a firm believer in teaching the fundamentals and has a gift for simplifying complex concepts.