Dealing with furnace problems can put a damper on RV life and camping excursions. Many RV owners face a common issue when the furnace fan runs, but hot air isn’t coming out of the vents or heating system.
This frustrating scenario usually happens when the furnace fails when there is a pilot light issue, and it fails to ignite, so the water heater doesn’t do its job. Without the burner kicking on to heat the internal heat exchanger, the fan’s blower pushes out unheated interior air.
The problem lies with igniting the propane burner, which requires several conditions to be met. There must be sufficient propane flow for the furnace to light, a working ignitor to spark the flame, proper electrical power, and a closed sail switch. Failure at any point prevents ignition.
Methodically inspecting the furnace system and testing components will usually reveal the culprit. In some RVS, removing the furnace is the only way to access the components. In our troubleshooting tips guide to RV faults, you can learn more about how RV owners get furnace heat back quickly without searching for the manual for your furnace.
By the end, you’ll see there is nothing better than proper maintenance and something you should add to your RV trip planner so you aren’t caught in the cold. (Read Frozen Pipes Underground)
How Does an RV Furnace Work?
Knowing the basics of how an RV furnace operates can help pinpoint where issues may arise. Here’s a quick overview:
- The thermostat calls for heat, signaling the furnace to ignite.
- Power (12V from the RV battery or 120V shore power) goes to the furnace control board.
- The sail switch closes, allowing propane to flow to the burner.
- The igniter creates a spark to light the propane burner.
- The burner heats the heat exchanger.
- The blower turns on and blows air across the heat exchanger to circulate warm air.
- Once the desired temperature is reached, the thermostat signals the furnace to shut off.
The furnace won’t produce heat properly if any part of this process fails.
Common Problem Why RV Furnace May Blow Cold Air
Several common culprits could cause an RV furnace fan to run but supply no or low heat:
Sail Switch
The sail switch is a safety component that prevents gas from flowing unless the furnace blower runs. If something stops the sail switch from closing properly, the burner won’t ignite. Visual inspection and testing with a multimeter can diagnose sail switch issues. Replacement is straightforward.
Fuel Source
Ensure propane tank levels are adequate and valves are open. Clogged propane lines, a faulty regulator, or a regulator adjusted for low pressure can also prevent sufficient gas flow. Inspect lines and connections for blockages. If needed, testing regulator pressure and replacing it typically solves fuel supply problems.
Gas Valve
The gas valve opens to allow propane into the burner. If stuck closed, dirty, or defective, gas won’t flow. First, check if the gas valve receives power when heat is called for. If so, cleaning or replacing the gas valve will often fix the problem.
Ignitor
The ignitor creates a spark to light the propane burner. If weak, intermittent, or failed, ignition won’t occur. Check for proper ignitor alignment in the burner chamber. Replace if corroded or if no spark is visible during the ignition sequence. (Read Starter Cable Wire)
Flame Sensor
The flame sensor confirms ignition by detecting the burner flame. If unable to sense flame, it will shut off gas flow. Inspect for corrosion, clean the sensor, and verify proper positioning in the burner tube. If the problem persists, replace the sensor.
Control Board
The furnace control board manages operation and troubleshooting diagnostics. Replacing the circuit board should restore normal function if it is not sending power to components. Consult diagnostic codes to help determine if the board needs replacement.
Blower Motor
Insufficient air flow results in low heat output if the blower fan motor fails to start or spins slowly. Lubricating the motor or replacing a worn-out motor will typically get the blower running properly again.
Heat Exchanger
Cracks or holes in the heat exchanger will prevent adequate heat transfer to the circulating air. Have an HVAC technician inspect for leaks or blockages. The entire furnace may need replacement if the heat exchanger is defective.
With a basic understanding of furnace components and failure points, we can tackle troubleshooting common RV furnace problems.
Common RV Furnace Problems
Below are frequent issues that arise when the fan will come on but there is no heat or not enough air blowing to generate heat in your RV:
RV Furnace Doesn’t Turn On
If the furnace doesn’t respond at all when the thermostat calls for heat, power delivery issues are most likely the culprit:
- Verify the furnace control board is receiving 12V power from the RV battery. Check the furnace fuse and replace it if blown.
- For a furnace wired into shore power, ensure the 120V supply is active. Reset circuit breakers if tripped. Test for power at the furnace control board.
- Inspect all wiring for damage. Repair or replace any corroded or broken wires.
- Ensure the propane tank valve is open and the furnace gas valve knob is on.
- Test components like the sail switch, gas valve solenoid, and blower motor for function. Replace if defective.
- If the circuit board is getting power, but the furnace doesn’t operate, the board probably needs replacement.
The Fan Runs, but There’s No Heat
If the fan comes on, but you only feel the cold air around the vents, the lack of burner ignition is likely preventing heat:
- Verify that the propane supply and exhaust venting are not obstructed.
- Inspect the ignitor for damage, corrosion, proper electrode gap, and positioning. Replace if faulty ignition persists.
- Check the flame sensor is clean and correctly positioned to detect burner flame.
- Ensure the gas valve is opening to allow fuel flow. Replace if defective.
- Low voltage from a weak RV battery could prevent ignition. Test the battery and recharge or replace it if needed.
The issue could also be a tripped limit switch, indicating overheating. Determine and address the overheating cause before resetting the limit switch. (Read Can Tvs Be Stored In The Cold)
The Furnace Stops and Starts Frequently
If the furnace cycles on and off repeatedly, the thermostat or propane supply systems may have issues:
- Dirty thermostat contacts can cause short cycling. Clean gently with rubbing alcohol.
- Adjust the thermostat deadband range so it doesn’t cycle too frequently. A wider gap between heat/cool modes prevents rapid switching.
- Inspect propane lines and connections for leaks causing pressure changes. Tighten fittings or replace damaged hoses and valves if needed.
- Ensure propane tank gas levels are adequate. Refill or switch tanks if low. Consider larger tanks to prevent repeated depletion.
Thermostat is at Set Temperature, But Furnace Doesn’t Shut Off
If the furnace keeps running when the interior reaches the desired temperature set at the thermostat, it shows a problem sensing thermostat signals:
- Faulty thermostat: Test it manually or replace it if unresponsive. Use a multimeter to check for continuity.
- Short circuit: Check and repair any spliced thermostat wires causing continuous closed circuit.
- Defective control board: If the properly wired thermostat has no continuity but still runs, replace the board.
Furnace Not Working on Battery
RV furnaces can operate on shore power or battery, but if the furnace only works on shore power, low battery voltage may be the issue:
- Test battery voltage under load. Charge the battery or replace it with a new deep-cycle battery if defective.
- Inspect fuses/breakers between the battery and furnace. Verify adequate wire gauge. Replace if needed.
- Connect the furnace to a different DC power source, like an inverter generator. If you get your furnace to start, insufficient battery voltage is likely.
- Ensure no switches disrupt battery power to the furnace. Reset or replace malfunctioning power transfer switches if present.
Weak Airflow Through Vents
Lackluster airflow: when you turn on, the furnace would have to work harder and run longer to reach the set temperature:
- Dirty air filters reduce air handling efficiency and your RV could be getting cold through lack of airflow. Check and change filters regularly.
- Ensure furniture, accessories, etc, don’t obstruct vents.
- The blower fan may need replacing if it’s making noise, binding, or failing to come up to speed.
- Look for crushed/disconnected ductwork or closed registers limiting airflow. Inspect and repair ducting so there is sufficient air passing through.
- Check for exhaust vent blockage or back-drafting because of wind direction.
Furnace Fan Makes Loud Noises
If you hear the fan and it is making unusual noises, you’ll need to check inside of the furnace and fan housing to see what is causing the fan noise.
- Lubricate the blower motor if necessary, but don’t over-oil. Check the fan turns easily.
- Inspect fan blades for obstructions and clean out debris if present.
- Check and replace worn-out belts/bearings in belt drive systems.
- Rotate the blower wheel and listen/feel for abnormal rubbing, scraping, or grinding.
- Replace the entire blower assembly if worn out or severely out of balance where the fan kept running and wearing.
RV Furnace Common Troubleshooting
When experiencing RV furnace problems, there are some general troubleshooting steps to take:
- Consult the owner’s manual for manufacturer-specific info like diagnostics codes.
- Inspect the furnace for obvious issues like dirt/debris accumulation, burnt/disconnected wires, or cracked heat exchanger. Clean fan and internal components with compressed air.
- Check that switches, valves, fuses, and breakers are properly set and that the fan kicks in when you turn the furnace on.
- Test the power supply to the furnace control board from shore power or the RV battery.
- Use a multimeter to check for continuity at wires, switches, sensors, and other components. Replace if defective.
- Observe diagnostic indicator lights on the furnace control board for trouble codes.
- Try a simple power reset by turning off the shore power/battery disconnect switch for 30 seconds and then switching back on.
- Carefully inspect propane connections for leaks with soapy water. Tighten fittings or replace damaged valves/hoses.
- Review your recent repair and maintenance activity in case something was disconnected.
- Have a technician perform electrical testing and combustion analysis annually before each camping season.
Do All RV Furnaces Have a Reset Button?
You won’t find every furnace inside of the RV has a reset, although many do. Newer models have this reset button on the control board to get the furnace going after a fault occurs.
Check the owner’s manual to see if your model has one and where you can find it. The reset button should be pressed whenever diagnostic lights show an issue in the RV heating system. Remember this resets all control board programming, so set the thermostat and operating modes again afterward. If resetting doesn’t resolve the issue, further diagnosis and repairs are likely needed.
Getting an RV furnace working properly again may take some troubleshooting, but methodically inspecting components and connections will usually reveal the underlying problem.
Maintain your furnace well between trips to avoid frustration when using it. But if issues arise when you turn your furnace off and it starts blowing cold air, it should help narrow down causes so you can get comforting heat restored quickly. (Learn How Much Weight Can A Single Axle Trailer Hold)
Conclusion: Does RV Furnace Troubleshooting Help?
When inside the RV and your RV furnace won’t operate properly, blowing cold air requires methodical troubleshooting to pinpoint the issue. Consult your owner’s manual for model-specific guidance and diagnostics, and use the information from our above troubleshooting guide. Inspect all furnace components and test for function.
The common problem is the ignition system, fuel supply, thermostat wiring, or sail switch malfunction. Replace damaged parts as needed. Consider preventive RV maintenance, like cleaning intake filters and ducts regularly and testing components before trips.
Annual professional service checks will help spot potential furnace issues and make sure your furnace is running properly. If DIY efforts don’t make the furnace start, it may be time to replace it or temporarily use a portable electric space heater.
With attention and care, your RV furnace can reliably heat your rig for many seasons of camping adventures.
FAQs: RV Furnace Issues
Why does my furnace blower run continuously?
Continuous blower operation can be caused by a faulty thermostat not signaling to turn off, a stuck limit switch due to overheating, a blown circuit board preventing the blower from shutting off, or a thermostat wiring short circuit.
How can I tell if my sail switch is bad?
You can test the sail switch using a multimeter to check for electrical continuity during the ignition sequence, listening for a click indicating the switch is closing when heat is called for, or bypassing the sail switch to test if the burner ignites properly.
Why does my furnace keep shutting off after a few minutes?
Frequent furnace shutdown after a few minutes can be caused by a dirty air filter restricting airflow, a faulty flame sensor unable to detect burner ignition, an improperly adjusted low gas pressure regulator, or a thermostat deadband range set too narrow.
How often should I have my RV furnace inspected?
The RV furnace should have an annual inspection by a certified technician. Monthly checks of the exhaust and air intake are recommended. The air filter should be cleaned every 2-3 months during frequent use. Operation on both propane and shore power should be tested before each trip.
