When an RV water heater gives no hot water, the makers' manuals point to four first checks: a tank left empty after storage, bypass valves still set for winter, propane or 12-volt power switched off, and a side that has locked out. Which side failed, gas or electric, points to the cause.
RV Water Heater Not Working: Gas, Electric and Tankless Checks
At a glance
- Which side stopped: gas and electric heat the same tank through separate switches and separate limits, so the side that quit tells you where to look.
- The reset: on current Suburban and Dometic tank heaters the reset is the switch itself, off for 5 to 30 seconds depending on brand, while the 2018 Atwood manual adds a push-button reset on the electric side.
- Where you stop: every manual read here reserves propane leaks, burner work, 120-volt wiring and relief valve replacement for a qualified technician.
On this page (10)
Start with the side that failed
A gas-electric tank heater is two heaters sharing one tank, each side with its own switch and its own temperature limit. If gas works and electric does not, look at the element, its switch or its limit. If electric works and gas does not, look at propane, 12-volt power and ignition.
Tip: On a Dometic WH-series heater running both sides, a gas lockout does not light the lockout lamp while the electric side works. Slow recovery is the clue; switch the electric side off to see it.
The first checks, in minutes
- Is the tank full? Suburban says to refill the heater and remove all air from tank and lines before lighting it or switching on power; running it dry can damage the tank and controls.
- Are the bypass valves back to normal? A winter bypass leaves the heater out of the system.
- Propane on and in the tank. Truma's troubleshooting table opens with the gas supply off, then an empty gas tank.
- 12-volt power on. The gas side needs it. Girard advises switching it off in storage, which is easy to forget in spring.
- The right switch. On Suburban DE models the element switch is behind the outside door; on DEL models it is the ELECTRIC rocker inside, and some DEL models have both.
If air spurts from the hot taps, open each hot faucet until no air comes out; a system that never builds pressure points to the pump (see RV water pump problems). Your model is on the data plate behind the outside access door.
How to reset it, by brand
Most makers reset by cycling a switch; the 2018 Atwood manual also has a button.
| Heater | Reset as the maker describes it |
|---|---|
| Suburban tank (D, DE, DEL), gas lockout | Red RESET light on the inside switch plate stays lit when ignition did not occur. Put the GAS rocker (or plain rocker) in OFF, wait five seconds, return it to ON. |
| Dometic WH-series, gas or electric | Correct the cause, then switch OFF and back ON. If the control switch light stays on longer than 15 seconds, switch OFF, wait 5 minutes, repeat. |
| Dometic WH-series, high water temperature | Investigate the cause of overheating first, let the water cool, switch OFF for 30 seconds, then ON. |
| Atwood 4, 6 and 10 gallon, electronic ignition | Remote switch light on longer than 15 seconds: OFF for 5 minutes, repeat. High water temperature lockout: OFF at least 30 seconds, then ON. On the electric side, press the manual reset high temperature limit switch with a pencil or other nonmetallic object. |
| Truma AquaGo | Note the LED 2 flash pattern, switch the appliance off, wait 5 seconds, switch on. At the control panel, off, wait 2 seconds, on. |
| Girard GSWH-2 | After two failed ignition trials the control locks out. Turn the hot water faucet off and back on. |
| Suburban ST-42 / ST-60 | After three failed trials for ignition, turn the control panel ON/OFF button off, then back on. |
From the Dometic WH-series manual, the 2018 Atwood/Dometic manual and the Suburban, Truma and Girard manuals. A lockout that returns after the reset goes to an authorized service center, per Suburban, Dometic and Truma.
Hot water on gas but not on electric
After the switch, check the overheat limit. Dometic says a failed thermostat opens the E.C.O. and locks the system out; check that the thermostat touches the tank firmly, then cycle the electric switch. Running the 120 VAC side with no water in the tank damages the element, Suburban warns.
Anything behind the element cover is 120-volt work for a licensed technician. Suburban and Dometic both warn against aftermarket add-on heating elements.
Will not light on gas
Suburban and Dometic tank heaters give the burner three tries, then lock out. Rule out air in the gas line first: a first start-up may need several ignition cycles to purge it, and after a propane tank change Suburban says to light a cooking burner inside the RV.
- Combustion air blocked. Check the screen in the outside door. Dometic warns that insects nest in the burner tube, causing poor combustion or delayed ignition.
- Soot anywhere on the heater. Suburban says to shut the unit down immediately and call a qualified service person.
- The board fuse. With Dometic's 2 amp board fuse blown, the heater will not operate. Find the short first and never fit a fuse larger than 3 amps.
- The thermal cut-off. A flue obstruction, or wind while driving, can trip this one-time device; the heater stays off until it is replaced. Never run the heater on gas while moving.
Tip: If you smell gas, Suburban says to evacuate the vehicle, shut off the gas at the container, touch no electrical switch, phone or radio inside, leave the engine and generator off, and call a gas supplier or qualified technician.
Lukewarm or not hot enough
On a tank heater, sediment slows heat transfer, so Dometic calls for draining the heater at least once a year. On Dometic EXT models, water that is not as hot points to a faulty mixing valve, a certified technician's job.
On tankless units, which need flow at the tap to fire, check:
- Minimum flow. Suburban's ST-42/ST-60 needs 0.7 gallons per minute, so do not use the shower-head pause button. Truma's AquaGo fires above roughly 0.4; Girard's manual gives both 0.80 and 0.90.
- Too many taps at once. Truma's warning W 29 means more heat is asked for than the unit can supply, even at 60,000 BTU. Use fewer hot taps.
- Very cold inlet water. Below roughly 45°F, Girard suggests turning down the hot water at the faucet.
- Scale. Truma lists lime scale as a cause of low temperature and boiling noises; descale it.
Tip: A Girard GSWH-2 or Suburban ST shower that goes cold after 20 minutes is not a fault: both shut off after 20 minutes of continuous running. Cycle the faucet or panel button to restart.
Water dripping from the relief valve
A relief valve that drips while the heater runs is often doing its job: heated water expands in a closed system, and Suburban says dripping does not mean the valve is defective. Dometic adds that the tank's air pocket gets absorbed over time. To restore it:
- Let the water cool and turn off the water supply or pump.
- Open the hot water faucet closest to the heater.
- Pull the relief valve handle straight out until water stops flowing.
- Let the valve snap shut, close the faucet, turn the water back on, then the heater.
Never plug the valve. For a persistent drip, Suburban and Dometic point to an expansion tank in the cold water line.
Tank versus tankless: which checks differ
| Check | Tank (Suburban, Atwood, Dometic) | Tankless (Truma, Girard, Suburban ST) |
|---|---|---|
| Power needed | 12 V for the gas side, 120 V for the element | Propane plus 12 V only |
| Fault display | A lockout lamp, usually no code | Error codes: LED flash patterns or a panel display |
| Starts heating when | The thermostat calls for heat | Flow at a hot tap exceeds the unit's minimum |
| Bypass check | Applies, bypass kit takes the tank out of the system | Applies to Truma; Girard says its heat exchanger needs no bypass kit |
| Periodic owner items | Drain and flush, anode rod (Suburban), relief valve air pocket | Inlet filter or screen, descaling |
| Freeze behavior | Drain for storage | Truma signals a freezing risk below 37.4°F (3°C); Girard's code Fd runs the burner briefly and protects only the heat exchanger |
On a Truma, the code itself is on the red LED behind the outside access panel, per Truma's tech tip.
Where you stop and call a technician
Suburban leaves all repairs to your dealer or a qualified technician, Girard rules out do-it-yourself installation, and Truma recommends a yearly service. Hand these over:
- Any propane smell, suspected leak, burner or gas valve work.
- Soot on the heater, or a heater that has been under water.
- 120-volt wiring, whether a water heater element or a rooftop air conditioner that will not cool.
- Replacing a relief valve, mixing valve or thermal cut-off.
- A lockout that returns after one reset.
Suburban's warning explains why: an appliance not kept in factory condition or not maintained properly raises the risk of fire and the production of carbon monoxide, which can cause personal injury, property damage or death.
Common questions
How do I reset my RV water heater?
Cycle the switch: off for five seconds on Suburban tank heaters and the Truma AquaGo, and 30 seconds on a Dometic after a high water temperature lockout. The 2018 Atwood manual adds a push-button reset on the electric side.
Why is my RV water heater not lighting?
Tank heaters try three times, then lock out. Look for propane off or empty, air in the line, no 12-volt power, or insects in the burner tube.
Why does my RV water heater work on gas but not electric?
The two sides are independent. Check the electric switch, then the overheat limit, which locks the electric side out until the switch is cycled.
What are the most common RV water heater problems?
In the makers' manuals: a tank not refilled after winter, bypass valves still set for winter, propane or 12-volt power off, a gas lockout, a tripped overheat limit, and a relief valve dripping from normal expansion. Tankless units add too little flow, too many taps at once and scale.