RV Water Heater Repair and Replacement

Steel tanks, aluminum tanks, and the anode question

Suburban builds a porcelain-lined steel tank. Steel corrodes, the porcelain lining is never perfect, and so those units carry a sacrificial magnesium or aluminum anode rod that corrodes preferentially and protects the tank. That rod is a consumable. Once it is eaten down to the wire core, the tank starts sacrificing itself instead, and the end of that story is a pinhole at the bottom seam and a wet compartment. Checking it annually is the cheapest maintenance on the entire vehicle.

Atwood, now sold under the Dometic name, builds an aluminum tank clad in steel. Aluminum forms its own protective oxide layer and needs no anode, which is why those units use a simple nylon drain plug. Installing a magnesium anode in an Atwood tank is actively harmful: the dissimilar metals set up a galvanic cell that attacks the aluminum. We see this mistake regularly, usually made by a well-meaning owner or a general handyman who assumed all water heaters take a rod. Identifying the brand takes ten seconds and prevents it.

Water chemistry drives the pace of all of this. Municipal water across much of Southern California is hard, and calcium scale accumulates on the tank floor and on the electric element where it acts as an insulator. Scale under an element causes the element to overheat and fail, and scale in the tank reduces effective capacity and can plug the drain. Flushing with a wand through the drain port, not just draining, is what actually removes it. Annually is the interval most units want.

Working through a no-hot-water complaint

These units usually offer two heat sources, and the fastest diagnostic step is checking whether both fail or only one. Electric-only failure with propane working normally points at the element, the thermostat, or the high limit on the electric side. Propane-only failure with electric working points at the gas valve, the igniter, the flame sense, or the direct spark ignition board. Both failing at once suggests a shared component: the thermostat assembly, the high limit switch, or a supply problem upstream.

The ECO, or energy cutoff, is the safety that trips most often and confuses most owners. It is a manual reset high limit clipped to the tank surface, and it opens when tank temperature exceeds roughly 180 degrees. It trips when the thermostat sticks closed, when the unit is run dry after winterization, or when heavy scale insulates the sensor from actual water temperature. Resetting it without finding the cause means it will trip again, and repeated trips work harden the bimetal until it stops protecting anything.

Direct spark ignition faults follow a similar logic to a furnace. The board energizes the gas valve, sparks, and looks for flame within a short trial period. No flame, or a flame it cannot sense, and the board locks out with a fault light. Rusted burner tubes, a spider web in the venturi, a corroded ground path at the burner bracket, or an igniter with an eroded gap all produce lockouts. Combustion deposits on the flue tube and baffle also reduce heat transfer badly enough that recovery time doubles.

Running a unit dry is the fastest way to destroy an electric element, and it is almost always a winterizing mistake or a bypass valve left in the wrong position. The element scorches within seconds without water around it. If an owner tells us the electric side quit right after de-winterizing, we check the element before anything else, and we check the bypass valve position because that is what allowed it.

Tankless units and hydronic systems

On-demand units from Girard and Truma trade tank capacity for continuous output, and they bring a different maintenance profile. They modulate the burner against flow rate, so they need a minimum flow to fire at all, and a partly clogged aerator or a low pump output can leave a unit that simply refuses to light on a trickle. Scale buildup in the heat exchanger is the main long-term enemy, and a descaling flush with a circulation pump is the service those units want on a schedule.

The cold water sandwich complaint on tankless is a design behavior rather than a fault. Shut the flow, then reopen it, and the slug of water sitting in the exchanger arrives hot, followed by cold water while the burner relights and ramps. Better units minimize it with a small buffer. Understanding it prevents a lot of pointless part replacement, and we explain it rather than selling a repair for it.

Hydronic systems on larger diesel coaches, most commonly AquaHot and Oasis, are a genuinely different piece of equipment. A diesel-fired burner heats a glycol loop, and that loop supplies both domestic hot water through a heat exchanger and cabin heat through fan-coil units in each zone. Electric elements provide a lower-output alternative on shore power. They are excellent systems and they are unforgiving of neglect.

The failure points on hydronic are specific: a fouled burner nozzle, a worn or carbon-crusted igniter, a failed circulation pump, air trapped in the loop, and glycol that has been left past its service interval until its corrosion inhibitors are exhausted and it starts eating the aluminum passages. Zone heat that works in one room and not another is nearly always an air lock or a dead zone pump rather than a burner issue. These are bay jobs with the coach inside, which is exactly what a 35,000 square foot facility is for.

Replacement, upgrades, and what fits

A tank that has perforated is not repairable, and anyone offering to patch one should be politely declined. The failure is corrosion through the wall, and the surrounding material is in the same condition even if it has not opened yet. Replacement is a bolt-in job when the new unit matches the old footprint, and the door and flange from the original opening usually carry over. Six and ten gallon units use different openings, so an upgrade in capacity means modifying the sidewall cutout and reframing it.

Converting from a tank unit to on-demand is a popular upgrade and it has prerequisites. Tankless burners consume substantially more propane per minute than a tank burner, and the gas line has to be sized for that draw or the unit will starve under load. The opening is a different size, the electrical draw for the control board and fan is higher, and water pump output has to meet the minimum activation flow. We check all four before quoting, because the disappointing version of this upgrade is one that works at the shop and not at a campground.

Wherever the unit sits, the surrounding structure gets inspected while it is out. A water heater compartment that has been wet is the single most common origin of subfloor rot on a travel trailer, since the bay sits low, drains poorly, and hides behind an access door nobody opens. If we find soft plywood at the opening, we say so and price the repair separately. Putting a new heater into a rotten opening is a job that has to be done twice.

What is included

Tank material identification

Steel versus aluminum confirmed before any anode rod decision, since the wrong choice attacks the tank.

Drain, flush, and descale

Wand flush through the drain port to clear calcium from the tank floor and off the electric element.

Dual heat source isolation

Electric and propane sides tested independently to narrow the fault to one circuit rather than guessing.

Burner and flue service

Burner tube, venturi, orifice, and flue baffle cleared of nesting debris and combustion deposits.

Safety device verification

Thermostat, high limit, and pressure relief valve checked for correct operation and correct reset behavior.

Compartment and structure inspection

The bay floor and opening frame checked for the water damage that hides behind a closed access door.

Signs you need this work

• Hot water on propane but nothing on electric, or the reverse
• A puddle or rust trail under the exterior access door after the unit sits overnight
• The pressure relief valve weeping every time the unit heats up
• Recovery time that has doubled compared with a year ago
• A fault light on the exterior panel that clears on reset and returns within a day
• A tankless unit that will not light unless the faucet is opened all the way