First, I owe you an apology. It has been a little while since our last blog entry. We’ve been very busy lately at AM Mobile RV Service, and the writing has taken a back seat. Thank you for your patience—and for keeping us busy.
With November trips and cooler Hill Country weather here, let’s talk about a problem worth checking before you leave home: your RV water heater makes hot water on propane, but not on electric.
Picture a weekend in Bandera. You’re plugged into a campground, you’ve selected electric water heating, and you’d rather save the propane. Later, the shower is cold. You switch to propane, wait for the tank to heat, and suddenly everything works.
That’s an illustrative example, not a diagnosis. But it raises the right question: if the tank can heat on propane, what is keeping the electric side from doing its job?
My approach is to answer that before recommending a heating element—or an entire replacement water heater.
First, make sure your heater actually has an electric heating mode
This article applies to dual-fuel tank water heaters: models that can heat stored water with a propane burner, a factory electric element, or both when approved by the manufacturer.
Not every RV water heater does that. A gas-only heater does not gain electric heating just because the RV is plugged in. Many propane tankless models use 12-volt electricity to operate their controls, but propane still supplies the heat. Suburban’s IW60 is one example.1
Find the model number and check its manual. “It has wires going to it” is not enough to identify an electric heating mode.
Propane and electric heat the same tank through different systems
On a dual-fuel tank heater, the burner and electric element are different heat sources. The electric element needs the correct AC power supply and a working control path.
Propane operation therefore does not prove the electric supply, switch, relay, element, or related controls are good. On some Dometic/Atwood models, 12-volt controls command a relay that passes separately supplied AC power to the element. Other designs use different control arrangements.2
That detail matters. There isn’t one universal wiring diagram, reset button, or thermostat arrangement for every RV water heater.
The owner checks I would start with
Confirm that the tank is properly filled
Before either heat source is turned on, the tank must be filled according to the manufacturer’s instructions, with unwanted air purged from the water lines. An electric element operated without water can be damaged. Propane operation with an empty tank can also damage the heater.1
A full fresh-water tank does not prove the water-heater tank is full. Neither does water flowing from a faucet if the water heater is still bypassed for winterization.
After draining or servicing, keep both heating modes off, verify the bypass valves are in their normal operating positions, and follow the manual’s filling procedure. With the plumbing correctly configured, running a hot faucet until the sputtering stops and water flows steadily is part of purging unwanted air.
If the heater may already have been operated dry, shut it down and allow it to cool before refilling or servicing. Adding water to an overheated, empty heater is not a safe shortcut.
Check the electric controls—not just the propane switch
Some installations have separate gas and electric switches inside the RV. Some also have an electric switch at the heater itself.
For example, Suburban’s operation guide places the electric switch for its DE models behind the exterior water-heater door. DEL models use an interior control, with some also having a secondary exterior switch. Other brands and model generations differ.3
Use the manual to identify your controls. An illuminated switch may indicate that electric mode has been selected; it is not proof that the element is heating.
Confirm the correct power source is available
The electric element needs its AC supply. A charged house battery alone is not enough. Shore power or generator power normally supplies that circuit; whether an inverter can supply it depends on how that RV is wired and equipped.
Check the ordinary power controls and note the position of the labeled water-heater breaker. A working lamp or microwave does not prove power is reaching the heater’s separate circuit.
If the breaker trips, don’t keep resetting it or install a larger one. Leave electric mode off and have the cause diagnosed. Burning smells, discolored wiring, melted parts, or any shock sensation are reasons to stop using the affected system and seek qualified service.
Allow for a genuine heating cycle
A tank that is already hot from propane may not call for electric heat until it cools enough. Conversely, warm water left over from propane operation does not prove the electric element is working.
For a meaningful comparison, the properly filled tank needs a heating demand, propane mode needs to be off, and electric mode needs the recovery time specified for that model. Don’t judge it after a few minutes—or assume every heater has the same recovery rate.
What a technician checks next
If the tank and controls are correctly set up but electric heating still fails, the next step is diagnosis of the electric circuit.
Depending on the model, possible causes include a failed heating element, a damaged switch or connection, a relay problem, or a thermostat or high-temperature safety-control issue. A technician checks the supply and control path rather than assuming the element is bad.2
An element replacement may be the right repair. It is not automatically the right repair.
This is also where owner troubleshooting should stop. Live-voltage tests, electrical-cover removal, component replacement, and safety-control testing belong with someone qualified to perform that work. Never bypass a thermostat, high-limit control, or other safety device to make the heater run.
“Burping” the water heater: why it matters—and what it means
I also want to address burping, because people use that term for two different things. Confusing them can lead to poor filling practices or unnecessary relief-valve replacement.
Purging unwanted air after filling
After a tank has been drained, air must be displaced as it fills. Air in the plumbing can make a hot faucet spit and sputter. The heater needs to be properly water-filled before heating begins, especially to protect the electric element.3
This is the filling and air-purging side of “burping.” It does not mean removing every bit of air from a tank designed to retain an expansion air pocket.
Restoring the designed expansion air pocket
Some tank water heaters are designed with an air pocket at the top. That pocket helps accommodate expansion as the water heats. Water expands when heated; the air pocket can compress to absorb some of that expansion in the RV’s closed plumbing system.1
Over time, that air pocket can diminish. Without adequate expansion space, pressure can rise during heating and the temperature-and-pressure relief valve may weep. Suburban explains that this does not automatically mean the valve is defective and provides an air-pocket restoration procedure. Dometic also publishes an air-gap restoration procedure.1
That is why restoring the air pocket—sometimes also called burping—can matter. It addresses expansion management. It is not a cure for a failed element or missing electric power.
Do it safely, using the correct procedure
Never pull the relief-valve lever on a hot water heater to “let a little air out.” Escaping water can cause severe scalding.
Dometic’s instructions specifically require the heater to be off and the stored water to be cool. The procedure also shuts off the water supply and opens a nearby hot faucet before operating the relief valve as directed. Follow the exact manufacturer procedure for your model, or have a qualified technician handle it.4
Do not deliberately leave the tank partly empty to create expansion space. A properly filled tank with its designed air pocket is different from an underfilled tank that exposes the element.
And never plug, cap, or disable the relief valve. Persistent dripping, heavy discharge, leakage when the heater is cool, or a valve that will not reseat needs investigation—not repeated burping. The technician may need to check supply pressure, temperature controls, the valve, or the need for an appropriately installed expansion tank.
This tank air-pocket advice is not a generic maintenance procedure for tankless water heaters.
Can you use propane while waiting for an electric repair?
Sometimes, but only if the heater’s condition and the nature of the fault make that appropriate.
Hot water on propane is not a complete safety inspection. If there is a leak, suspected freeze damage, overheating, electrical burning, soot, or a gas smell, don’t use propane mode as a workaround. Have the heater checked.
If the problem is confirmed to be isolated to the electric heating circuit and propane operation is safe, that may give you an option while repairs are arranged. Follow the manufacturer’s instructions and the technician’s recommendation.
If you smell gas, evacuate the RV, avoid electrical switches and ignition sources, and call qualified help from outside. Do not operate the heater.3
Check it before the holiday trip
Before a November trip around Bandera, Kerrville, or Fredericksburg, test each approved heating mode separately while you still have time to address a problem.
Check the filling and bypass setup, confirm the controls, and inspect for visible leaks. If the relief valve is weeping, have the expansion air pocket and the reason for the discharge evaluated instead of immediately ordering a valve.
My advice is simple: find out what failed before replacing what still works. Losing electric heat does not automatically mean losing the whole water heater.
AM Mobile RV Service provides mobile water-heater troubleshooting and repair in Bandera, Kerrville, Hondo, Tarpley, Fredericksburg, and the surrounding Texas Hill Country.
Call (512) 550-9579 to schedule service.
AM Mobile RV Service is not sponsored by, affiliated with, paid by, or receiving a commission from the manufacturers referenced here. The sources below support the technical explanations; they are not paid endorsements.
References
- Suburban RV — Product FAQs. Dual-fuel operation, dry-tank damage, tankless IW60 operation, and thermal-expansion air-pocket guidance.
- Dometic — Water Heaters Technical Training, 2019–2020. Model identification and AC-element/12-volt-control architecture. This is model-specific technical material, not an owner repair procedure.
- Suburban — Tank Water Heaters Operation & Maintenance Guide, March 22, 2023. Electric controls, tank-filling requirements, storage precautions, and safety warnings.
- Dometic Support — How to Replace the Air Gap. Manufacturer air-gap restoration guidance and explicit scalding precautions.
Always use the current manuals for the exact water heater and RV you own. Switch locations, control circuits, reset methods, and expansion provisions vary by model.