There are currently 4 different water heater types you might find in an RV. The two most common are from Suburban and Atwood. New to the RV world are the On Demand Water Heaters and in higher end motor homes you might find a system that provides both heat and hot water called Aqua Hot.
Maintenance on Atwood heaters is pretty simple. About once a year usually when you winterize, you want to clean out the water heater holding tank really well. The best way is to take out the drain plug. Caution here: Make sure the tank is cool and that the power and propane are off to the water heater. You do not want the heater to begin trying to heat the water when the tank is empty.
Once you have removed the drain plug, flush the tank with plenty of water to remove the loose calcium. Next you will need some white vinegar. About a gallon for the 10 gallon water heater. This is a good time to also clean the water holding tank on the RV. Perform the same basic steps, drain the water in the holding tank, flush to remove the calcium and then using a ration of 1:10 (vinegar to water) fill the holding tank. If you are doing the holding tank at the same time it will make it easier to do the how water system. Fill the holding tank with vinegar and then pump it into the hot water tank (make sure you put the plug in the water heater before filling).
Once the vinegar and water are in the tank(s) let it sit for a couple of days. The acid in the vinegar will loosen the calcium.
After a couple of days, drain and flush the system(s). If you are working on a Suburban Hot Water system, now is a good time to replace the Anode Rod.
Then Anode rod is to protect the insides of the steel tanks used in Suburban water heaters from rusting due to chemical reactions in the water. The Anode rod is made of a mixture of Zinc, Magnesium and Aluminum. Which reacts quicker to the chemicals in water that can rust the steel tank. Failure to replace the anode rod as needed results in the water tank rusting out and having to replace it sooner than needed otherwise.
That is it for the normal water heaters found in most RVs. I am still researching the maintenance of on demand and Aqua Hot systems. Those will be covered in the next article.