An RV furnace starts the blower first and lights the burner about 30 seconds later. If it fails to light three times, it locks out. Nearly every no-heat call comes down to one of three things: power, propane, or blocked air.
RV Furnace Not Working: What to Check When the Propane Heat Fails
At a glance
- Why it blows cold: after a failed light the blower keeps running, 5 minutes on a Suburban and 3 on a mid-size Atwood, before it shuts off.
- What you can check tonight: the fuse and the furnace switch, the tank valve fully open, the outside vent clear of snow and nests, and all registers and the return air grill open.
- What it burns: a 30,000 BTU furnace works out to about 0.33 gallons of propane per hour of burner time (calculated below).
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What happens when you turn the thermostat up
Knowing the normal order shows you where yours stops. With the propane valve fully open and the thermostat set above room temperature, the blower comes on, and about 30 seconds later the burner lights by itself. Never try to light it by hand. Suburban, Atwood and Dometic furnaces all follow this order.
If the burner does not catch, Suburban says to stop after three attempts, turn the furnace off and call a dealer or RV service agency, not to keep cycling the thermostat. A Suburban blower runs for 5 minutes in lockout, then you reset at the thermostat; a mid-size Atwood's goes off in 3 minutes. Dometic allows a reset, thermostat OFF for 10 seconds and back ON, up to three times if there is air in the propane line.
Tip: The order the furnace runs in tells you where it stopped. Nothing at all, not even the fan, points at 12 V power: a fuse, a switch, a flat battery. Blower but no flame points at gas or ignition. Lights and then quits points at airflow and the limit switch.
Match your symptom
Find the line that matches what your furnace is doing, then work the causes in order.
| Symptom (makers' words) | Causes the makers list | Your part of it |
|---|---|---|
| "The furnace will not light, the blower does not turn on" | Blown fuse; furnace breaker switch tripped or off; furnace in lockout; vents blocked; 12 V power low | Check the main fuse panel and replace a blown fuse; reset at the thermostat; clear the vents. Dometic sends a tripped furnace breaker to a technician. |
| "The furnace will not light, the blower turns on" | Air in the propane line; thermostat not set to Heat or high enough | Run a cooktop burner, which sits further downstream from the tanks, then try the furnace again; check the thermostat setting. |
| "The furnace shuts off before the desired temperature is reached" | Vents blocked or obstructed | Clean the vents and clear any obstructions. |
| "Furnace does not ignite and/or cycles frequently" | Tank not full; obstruction over the exhaust; furnace fuse; blocked return air grill; closed heat registers; no 12 V power | Work the list in that order, then call the dealer if it persists. Do not attempt to repair or adjust the furnace. |
Rows 1 to 3: Dometic's 2025 DF Series operating manual and its installation manuals. Row 4: Grand Design's Momentum owner's manual.
Power, switches and the thermostat
If nothing happens at all, start here: the furnace burns propane but needs 12-volt power to light. Three things cut that power or the call for heat:
- The thermostat, which has to be on Heat and set above room temperature.
- The furnace fuse in the main panel, and on larger Dometic models a dedicated circuit breaker there.
- The furnace's own power switch, inside the door on door models and on the outside on non-door models.
On a Suburban SF-Q furnace, a valve shut-off switch left OFF runs the motor for 30 seconds, passes no gas, then locks out until the thermostat or unit power is cycled. That looks exactly like a serious fault.
Tip: Low battery voltage alone will stop a furnace that has nothing wrong with it. Dometic's control board flags a low-voltage fault at 8 V to 9 V, and Truma tells VarioHeat owners below 10.4 V to charge the battery. Suburban gives no minimum voltage. Dometic also says never to power a 12 V furnace from a battery charger, even for testing.
Propane and air you can check yourself
Most gas and airflow causes need nothing more than a flashlight. The manual shut-off valve or the tank valve has to be fully open, never partly closed, Suburban says. If the stove and water heater are weak too, the trouble is upstream, at the propane regulator or the tanks, not the furnace.
Outside, look at the furnace vent. Dometic warns never to let snow or any object block the exhaust, and says to inspect it monthly for obstructions or soot and brush the exhaust tube clear. Watch for slush, ice, leaves and bug nests, and never fit a screen over the vent; neither Dometic nor Suburban allows one.
Inside, keep every heat register open, the return air grill clear, and doors to bedrooms and the bathroom open while the furnace runs, because the return air only pulls from the space around the furnace.
Tip: Check that no door on the RV blocks the furnace vent when it swings open. A propped-open compartment door or entry door over the vent is easy to miss in the dark.
How much propane it burns
Divide the furnace's BTU input by the energy in a gallon of propane. The Propane Education & Research Council puts propane at 91,502 BTU per gallon.
| Furnace BTU input | Gallons per hour of burner time (calculated) |
|---|---|
| 16,000 | 0.17 |
| 30,000 | 0.33 |
| 40,000 | 0.44 |
BTU inputs from Dometic's 2025 DF Series technical data; 30,000 divided by 91,502 is 0.33, and the other rows are worked the same way. That is per hour the burner is alight, not per hour of the night, because the furnace cycles. Grand Design and Jayco warn that in cold or windy weather consumption can be extremely high. How long a full bottle lasts is on the propane tank page.
Where to stop
Some parts are never owner work, and some signs mean shut it down now. The gas valve, the burner, and any sail switch or limit switch adjustment are technician work. Dometic says never to repair the furnace yourself, and Suburban warns: "Improper adjustment, alteration, service, maintenance or installation can cause serious injury or death."
Shut the furnace down and call a dealer or qualified technician if any of these apply:
- Soot at the vent, which Suburban calls a warning that combustion is incomplete and the furnace is unsafe.
- The furnace cycles erratically or delays on ignition.
- Any part of the furnace has been under water.
- It overheats or the gas does not shut off. Shut the manual gas valve first, then the electrical supply.
Suburban's carbon-monoxide warning: "Failure to follow instructions could result in severe personal injury or death due to carbon-monoxide poisoning, if combustion products infiltrate into the building." Dometic adds that the furnace can produce carbon monoxide, "which has no odor and can be life-threatening." A sounding propane alarm or CO alarm is not a nuisance to be muted.
If you smell propane, both manuals give the same steps:
- Evacuate all persons from the vehicle.
- Shut off the gas supply at the gas container or source.
- Do not touch any electrical switch, or use any phone or radio in the vehicle.
- Do not start the vehicle's engine or electric generator.
- Contact the nearest gas supplier or qualified service technician for repairs, or the fire department if neither can be reached.
- Do not turn on the gas supply until the leak has been repaired.
Common questions
How much propane does an RV furnace use?
A 30,000 BTU furnace burns about 0.33 gallons per hour of burner time. Propane weighs 4.2 lb per gallon at 60°F (16°C), so that hour is a bit under a pound and a half. A mild night uses less, because the burner cycles off.
Is it safe to run the RV furnace overnight?
The furnace is the one heater built for it, because its combustion is vented outside; Forest River says to heat only with the furnace, never the range. The combination CO and propane alarm must work, and Jayco notes it runs off the house batteries and fails if the battery cable is disconnected. Test it before each trip and at least weekly in use.
Why does my RV furnace blow cold air?
The blower has 12 V power but the burner is not lighting, and a furnace in lockout keeps the fan turning a few more minutes. On a Dometic the control board flashes a fault code, but it sits inside the furnace, and opening the furnace is technician work.
Why does my RV furnace keep shutting off?
Restricted ducting makes a furnace cycle on its high temperature limit, which is why Suburban forbids duct-mounted air boosters. If it still cycles erratically with registers open and the return air grill and exhaust clear, Suburban and Dometic both say to shut it down and call a service agency.