RV Water Heater Care

Taking preventive steps helps extend the life of typical Atwood or Suburban units.

By Gary Bunzer
March 2017

Neglecting the periodic maintenance that all motorhomes require can lead to expensive repairs and vacation delays. One easy-to-forget component that needs annual attention is the RV water heater. Mounted outside, out of sight and out of mind, it often ends up relegated to a lesser place behind the more prominent motorhome maintenance mandates.

The importance of RV water heater preventive maintenance is enhanced by the fact that the unit links to at least four of the major motorhome systems — the 12-volt-DC system, the 120-volt-AC system, the fresh-water system, and the propane system. A fifth possibility is the motorhome cooling system (for those water heaters with the motor-aid feature). Problems in any of those systems often affect the operation of the water heater, and vice versa, if maintenance is left unaddressed. So, with the RV water heater as the common denominator, I’ll break down those four systems and the water heater maintenance aspects associated with each.

12-Volt-DC Electrical System

Almost all RV water heaters today are electronically controlled, powered by the 12-volt battery system. (Some smaller RVs or older motorhomes may be equipped with pilot-model water heaters, but they are in the minority.) Proper DC voltage for all electronic water heaters is paramount, as is the negative or ground connection.

The printed circuit board, which controls the entire ignition sequence and beyond, is the central component on a water heater that utilizes DC electricity. A range between 10.5 volts DC and 13.5 volts DC assures proper water heater operation. Too much voltage from a runaway converter or not enough voltage from a depleted battery bank will have an adverse effect. Maintaining a healthy battery bank cannot be overemphasized.

Just as important are the ground connections. Proper grounding of the battery bank, as well as the water heater itself, is often overlooked. The not-so-robust grounding screw on the water heater easily can corrode or loosen. Check the cleanliness and tightness of this connection often.

When electrical energy passes through a mechanical connection (circuit board contacts especially), a type of corrosion, called dendrite, forms. It is difficult to remove by abrasive cleaning and must be attacked chemically. I recommend using a product called DeoxIT to treat the board contact strip and eliminate the dendrite. Perform this task annually, especially if the motorhome is exposed to salt spray. In fact, it’s quite all right to apply DeoxIT to any electrical connection on either electrical system. I use it on ground connections, fuses, battery terminals, etc. — anywhere a wire terminates or connects to another wire. Take a look at any RV water heater and you’ll find many connections that could benefit from DeoxIT. Keep in mind that most all water heater connections are outside the coach and exposed to the elements.

120-Volt-AC Electrical System

Many RV water heaters, much like some absorption refrigerators, are multisource devices — they can be powered by three different energy sources. One of those sources is the 120-volt-AC electrical system. An AC heating element is submersed in the tank of the heater, giving the user the option of heating the water with electricity from the grid or with onboard generator power.

Never start a heating cycle without water in the tank of the heater. Get in the habit of filling the tank before switching on the 120 volts AC to avoid damaging the heater element. If it’s necessary to replace heating elements, use factory replacement parts only, and avoid installing an aftermarket heating element in the tank drain fitting.

Fresh-Water System

Positioned smack in the middle of the fresh-water plumbing system, the water heater can be a source of obnoxious odors if the system is not cleaned, flushed, and sanitized regularly.

Cleaning and flushing instructions are as follows:

• Turn off all electrical and water sources and open the pressure and temperature (P&T) relief valve to release the system pressure.
• Remove the drain plug and drain the inner tank.
• Remove the P&T relief valve. In some cases this may require a special tool, available from RV parts and accessory stores.
• Create a mixture of 65 percent white vinegar to 35 percent clean water, enough to fill the water heater. For example, a si*gallon heater will require approximately four gallons of vinegar and two gallons of water.
• Reinstall the drain plug.
• Using a funnel, pour the vinegar/water mixture into the heater through the fitting where the P&T valve was located.
• Reinstall the P&T relief valve.
• Turn on a water source and run the heater through a few heating cycles, thereby reheating the mixture as it courses through the hot plumbing system. Continue until the odor of the vinegar is noticeable at each hot faucet.
• After turning off the heater and water supply, remove the system pressure and drain the heater once again.
• Using a garden-hose attachment with a 90-degree tip, flush remaining mineral sediments from the very bottom of the tank by carefully inserting the hose attachment and spraying all around inside the tank.
• Some people shoot compressed air through the P&T fitting while the drain plug is removed, thereby forcing all contaminants out of the inner tank. But I do not recommend this if backflow preventers (check valves) are installed at the water heater hot-outlet or cold-inlet fittings. It’s possible sediment can be forced into the check valve, rendering the seal or seat faulty.
• Continue until the draining water runs clear, and then reinstall the drain plug.

Sanitizing The System

Following are the steps to sanitize the entire fresh-water system, including the water heater.

• If the system is equipped with water purification equipment and/or filtering cartridges, remove or bypass them.
• Mix 1/4 cup of unscented household bleach (sodium hypochlorite) with one gallon of fresh water.
• Fill the tank by pouring one gallon of this mixture into the gravity fill of the fresh-water storage tank for every 15 gallons of tank capacity. If the coach is not equipped with a gravity fill for the fresh-water tank, use a funnel to pour each gallon of the mixture directly into the fresh-water hose before connecting it to the city water connection. Some motorhomes are equipped with an alternative method of pumping the chlorinated mixture directly into the fresh-water system; the mixture may be pumped through a tee fitting and a short hose installed between the water pump and the fresh water container, or via a separate RV antifreeze tank.
• Turn on the water pump and open every hot and cold faucet in the motorhome, including exterior faucets and showerheads.
• Allow the solution to pump completely through the system until the distinct odor of chlorine is present at every fixture. Don’t forget to run the solution through the toilet as well.

Cont.

• Close all the faucets and turn off the water pump.
• Allow the system to stand dormant for four hours. This will chlorinate and disinfect the entire system to a residual concentration of 50 ppm (parts per million), including the fresh-water tank, the water heater, the faucets, the piping system, and all fittings. (If 100 ppm residual concentration is required or desired, use 1/2 cup of bleach with each gallon of solution, instead of 1/4 cup, and let it stand for one to two hours.)
• After four hours, open the P&T relief valve to release the system pressure and remove the drain plug.
• Activate a water source and allow the water heater to drain as water is entering.
• Continue to flush until the odor and/or taste of the chorine diminishes to your satisfaction.
• After turning off the water supply, reinstall the drain plug.

If the motorhome is equipped with a Suburban water heater, a depleted anode rod may also cause odors in the system. Atwood water heaters do not require an anode. Inspect the anode in the Suburban heater periodically and replace it when it has been reduced to 25 percent of its original size.

Excessive Dropping Of Heated Water

Another fresh-water concern associated with the RV water heater is excessive dripping of heated water from the P&T relief valve. It is normal for a little water to drip from the valve during every heating cycle, but certainly not a lot. Excessive or constant dripping is a sure sign that the expansion area inside the heater tank has filled with water.

In essence, the hydrogen component in the water absorbs the hydrogen component in the air above the water inside the tank, and so the tank fills over time. As the water is heated without an expansion space above it, the P&T valve opens and the water is expelled. Excessive dripping from the P&T valve indicates the need to replenish the expansion pocket inside the water heater.

Here’s how to do it:

• Deactivate the water heater and turn off all sources of water.
• Open all the hot faucets inside the motorhome.
• Open the P&T relief valve by pulling the lever straight out.
• Close the P&T valve when water stops dripping.
• Turn on a water source.
• Close all the hot-water faucets when water is flowing smoothly from each.

Propane System

Of the four major systems related to the RV water heater, the propane gas system may be the most challenging for motorhome owners. A comprehensive understanding requires reverting to the circuit board mentioned earlier.

The typical circuit board performs three main water heater functions. It opens the gas valve, allowing fuel to be delivered to the burner area. It creates the high-voltage spark that ignites the gas. And while the flame is burning, the circuit board monitors the fire and stands ready to shut off the gas flow should the flame be extinguished during the heating cycle. It’s a workhorse!

For the water heater to work properly, it must be fed the proper amount of propane gas, delivered at the correct operating pressure. This requires a series of measurements and adjustments at the pressure regulator mounted near the propane tank, which is built to American Society of Mechanical Engineers (ASME) standards. Most motorhome owners don’t have the expertise to tackle this as a DIY project, so I highly recommend that a trained and certified RV service technician check the motorhome propane system annually. To watch FMCA’s Motorhome House Calls online video that explains the pressure regulator tests, visit www.goo.gl/iUe3DG.

The correct gas pressure entering the water heater is only half the equation. The other half is the physical alignment of the gas components. For proper and complete combustion, a straight line must exist from the point where the gas exits the orifice fitting in the gas valve to the point where it enters the mixing tube. Also, the orifice opening must be centered (in all directions) into the open end of the mixing tube.

Importance of The Alignment

Without this straight-through alignment, the propane/air mixture will be inconsistent, which will lead to flame flashback, incomplete combustion, sooting, carbon monoxide emissions, and possibly flame outage. The gas valve and burner tube can be manipulated by hand to reposition the components into a straight alignment.

Periodically remove the L-shaped burner tube and check for blockages (such as spider nests) that can disrupt the flow of gas and air to the burner. Adjust the air shutter to achieve a bright blue flame.

Also take a close look at the electrode assembly. It’s likely the most problematic of all the gas components in the water heater. Frequently the probe or probes can become covered with a layer of carbon buildup. Simply brighten the probes with 0000 steel wool. Be careful not to reposition the spacing between any two probes (if so equipped).

The 2 1/2-inch flue pipe also should be blown clean periodically. Be sure to wear eye protection, since debris will exit the exhaust port when compressed air is blown into the burner opening.

Winterizing The Water Heater

Most water heaters today are equipped with a bypass kit (available from RV parts stores). This is a way of isolating the water heater from the rest of the fresh-water distribution system. To properly winterize the water heater, use the following procedure:

• Begin by turning off all water sources.
• Remove the heater drain plug.
• Open the P&T relief valve by pulling the lever straight out.
• While draining, turn on a water source and allow the incoming water to flush out the tank as it drains. Continue flushing until the outgoing water has no mineral contaminants.
• Turn off the water source.
• Set the bypass valves to the “bypass” position.
• After draining, reinstall the drain plug, but only finger-tight. When draining is complete, a couple quarts of water will remain in the bottom of the water heater tank. This poses no threat of freeze damage.
• Close the P&T relief valve.

The water heater is now isolated from the rest of the fresh-water plumbing system. RV antifreeze can be distributed throughout the cold and hot tubing without the expense of filling the water heater.

When completed annually, these easy-to-perform preventive steps will help extend the life of the typical Atwood or Suburban RV water heater. To watch a visual explanation of many of these procedures, check out FMCA’s Motorhome House Calls online video at www.goo.gl/qwxwws.

And remember, RVing is more than a hobby; it’s a lifestyle!