RV water heater works on propane but not electric: what to check

Many RV water heaters have two separate heat sources: propane and a 120-volt electric element. When the heater works on propane but not electric, that is useful diagnostic information. It usually means the tank has water, the hot-water plumbing is connected, and the thermostat/ECO may be partly functioning, but the electric side is not receiving power or the element cannot heat.

First confirm this is not a bypass or mixing problem

If water is only lukewarm on both propane and electric, check the water-heater bypass valves and shower mixing valves first. But if propane mode produces properly hot water and electric mode stays cold after a normal recovery period, focus on the electric heating circuit.

Check the obvious switches

Some RVs have an inside electric-water-heater switch, an outside switch on the water heater itself, or both. The outside switch may be small and easy to miss. Make sure the correct switch is on, and confirm you are not confusing the gas switch with the electric switch.

Verify 120-volt power to the water heater

The electric element needs shore power, generator power, or inverter/charger pass-through if the RV is designed that way. Reset the water-heater breaker fully off and back on. If the breaker trips again, stop resetting it and treat that as a fault, not an inconvenience.

Some water heaters plug into a receptacle behind a cabinet or access panel. Others are hardwired. A qualified person can verify whether 120 volts reaches the heater, but do not open live wiring compartments if you are not trained for mains-voltage work.

Look for ECO or high-limit reset buttons

Many tank-style RV water heaters have small reset buttons near the thermostat/ECO area behind the exterior access panel. If an over-temperature condition opened the limit, the electric side may not heat until reset. A limit that trips repeatedly needs diagnosis; do not keep resetting it and ignoring the cause.

Suspect the heating element after dry firing or winterization

A failed electric element is common after the water heater was accidentally switched on while the tank was empty. This often happens after winterization, de-winterizing, storage, or when someone flips all breakers on before filling the tank. A burned element may not look damaged from outside.

Element testing requires power off, pressure relieved, and a meter check for resistance and short-to-ground. Replacement also requires the correct element style, socket, sealing surface and torque. If the tank threads are damaged or corroded, stop before creating a larger leak.

Do not overlook control boards on combination heaters

Some water heaters use electronic controls for both propane and electric modes. In those systems, the board may allow propane operation but fail to energize the electric relay. Model-specific service information matters here; Atwood/Dometic, Suburban and newer tankless/instant systems do not all diagnose the same way.

When to call a professional

Call an RV technician or qualified electrician if the breaker trips, wiring is heat damaged, the element tests shorted, the tank shows corrosion, you are not comfortable with 120-volt testing, or the water heater is a tankless model with error codes.