Quick answer: Dometic’s manuals point to a short set of checks for a heater that does nothing: water in the tank, the LP and water supply turned on, the 2-amp fuse on the control board, and a safety lockout after the heater failed to light or overheated. Check those first. If you smell propane or a carbon monoxide alarm sounds, stop, leave the RV and call a qualified RV technician or your gas supplier.
Safety first: gas smell. Dometic’s printed instruction for a gas smell is to get everyone out of the vehicle and shut off the gas at the container or source. Do not touch any electrical switch or use a phone or radio in the vehicle, and do not start the engine or generator. Contact a gas supplier or qualified service technician. If you cannot reach one, call the fire department. Do not turn the gas back on until the leak has been repaired.
This guide covers Dometic gas and gas/electric heaters, because those are the manuals we reviewed. Suburban and Atwood units differ, so use your own manual for exact switch positions. For a heater that works but leaks, see our guide to finding RV water damage early.
What should I check before anything else?
- Water in the tank. Dometic says not to operate the heater without water in the tank, and warns that powering the electric element while it is not covered by water can burn the element out and void the warranty.
- LP and water turned on. Dometic’s general information says both the LP and the water system must be on.
- Vents and combustion air grill clear. Keep them free of obstructions.
- Two-week rule. If the heater has sat unused for more than two weeks, Dometic warns that hydrogen gas may have formed in the hot water line. Open the hot faucet at the kitchen sink for several minutes before using any electrical appliance connected to the hot water system. A sound like air escaping from the pipe is the sign.
- Never run the gas side while driving. Dometic says gas appliances must not operate while the vehicle moves, because wind can cause flame reversal in the burner tube. It can also trip the thermal cut-off and shut the heater down until the part is replaced. Turn the gas off at the LP tank when the vehicle is in motion.
Symptom table: what you see and what the manual says
| Symptom | What the manufacturer lists as a cause | First owner check | Call a technician when |
|---|---|---|---|
| Nothing happens, no switch light | Blown fuse on the control board, or voltage problem at the unit | Look at the board fuse. Dometic specifies a 2 amp mini ATO type and says never install more than 3 amps | The fuse blows again (Dometic says to check for a short outside the board first), or Dometic’s voltage checks fail (more than 14 V to the unit, or below 10 VDC on the thermostat line) |
| Remote switch light stays on longer than 15 seconds | Gas did not light | Switch OFF, wait 5 minutes, try again (Dometic) | It repeats |
| Red lockout lamp on | No ignition after three attempts, or the safety switch tripped on high water temperature | Let the water cool. Switch OFF for 30 seconds, then ON (Dometic) | Lockout returns. Dometic says to contact a service center |
| Electric works, gas does not (combo units) | Gas side is locked out. The lamp may not light because electric mode still runs | Slow recovery is the clue. Switch the control OFF and watch for the lamp | Any burner, valve or gas pressure work |
| Yellow, lazy or sooty flame; popping | Insect or mud-wasp nests in the burner tube cause poor combustion and delayed ignition | Look for nests only if you can do so safely with the gas off | Nests cannot be removed easily, or there is soot (Dometic says soot means the flue needs adjusting) |
| Dead after driving with the gas on, or after a flue blockage | Heat melted the thermal cut-off, which cuts power to stop the heater | None. The blockage must be removed and the part replaced | Always |
| Rotten egg smell in hot water | Dometic: hydrogen sulfide, from the tank cladding reacting with sulfur in the water | The manual describes a vinegar-solution flush | Smell is in the air, not the water: treat as a gas leak |
Decision tree: gas, electric or neither?
- Do you smell gas, or has a CO alarm sounded?
- Yes: follow the safety box above. Stop here.
- No: does the heater have water?
- No: fill the tank first. Do not power the element dry.
- Yes: does anything respond (switch light, burner click, element heating)?
- Nothing responds: check the 12V supply and the 2 amp board fuse.
- A new fuse that blows again means a short. Call a technician.
- Electric works, gas does not: suspect a gas-side lockout.
- Reset once as above. If it locks out again, call a technician. Do not adjust gas parts yourself.
- Gas works, electric does not: confirm the electric switch is on and the RV has 120V power.
- Do not open panels or touch 120V wiring. Call an electrician or RV technician.
- Nothing responds: check the 12V supply and the 2 amp board fuse.
What should I leave to a professional?
Dometic states that installation and service must be done by a qualified service technician, service center, OEM or gas supplier. These jobs belong in that category:
- Gas pressure testing. Dometic says to test periodically, and gives the target as 11 inches of water column with three appliances running.
- Burner, orifice, electrode, gas valve and flue work.
- Replacing the thermal cut-off or tracing why it melted.
- Anything on 120V wiring, including the electric element circuit.
- Aftermarket heating elements. Dometic warns they can lack critical safety controls, and says alterations void the warranty.
When should I call a technician?
- You smelled gas, or a CO alarm has gone off. Dometic’s manual warns that gas flames consume oxygen and that ignoring the carbon monoxide warning can result in death or serious injury. Treat the alarm as real.
- A lockout repeats after one reset.
- The board fuse blows a second time.
- You see soot, a yellow flame, or cannot remove nests easily.
- You are unsure about any step. Gas and 120V mistakes are not worth the risk.
If you are weighing a repair against coverage, our extended warranty guide lists what service contracts commonly leave out. A gas fridge shares the same propane safety rules; see RV fridge not cooling.
FAQ
Why does my RV water heater work on electric but not on gas?
On Dometic combo units the gas side makes three ignition attempts and then locks out, and the lamp may stay dark because electric mode still runs. Dometic says the LP supply must be on, warns that insect nests in the burner tube cause poor combustion, and says gas pressure should be tested periodically. Leave nests you cannot easily remove, and any pressure testing, to a technician.
Is a dripping relief valve a sign the heater is bad?
Not by itself. Dometic says a pressure-temperature relief valve that drips while the heater is running does not mean it is defective, because water expands as it heats in a closed RV system. Its manual describes restoring the tank air gap and recommends an expansion tank or inlet pressure relief valve as a permanent fix. Scalding is a risk, so follow the manual warnings.
How often should I drain the water heater?
Dometic says at least once a year, and before winter storage or when freezing is possible. If you use the RV often or for long periods, it says flushing several times a year prolongs tank life. Let the water cool first.
Can I run the gas water heater while driving?
No. Dometic says gas appliances must never operate while the vehicle is moving and says to turn the gas off at the LP tank in transit.
My hot water smells like rotten eggs. Is that a gas leak?
Dometic attributes a rotten egg odor in the water to hydrogen sulfide and describes a vinegar flush. If you smell it in the air around the RV, treat it as a possible gas leak and follow the safety box.
Sources
- Dometic L.P. Gas Water Heater Installation and Operation Manual (WH-6GA, 6GEA, 9GEA, 10GEA, 16GEA): lockout behavior, 2 amp fuse, thermal cut-off, gas-while-driving warning, hydrogen gas caution, gas smell steps, annual draining
- Dometic L.P. Gas Water Heater Manual, 4-6-10 gallon (MPD 93756): “do not operate without water in tank”, LP and water on, vent clearance, burner nests, relief valve dripping, flushing and rotten-egg odor, aftermarket elements
Last reviewed: 2026-10-18
