RV Furnace Troubleshooting: Common Problems to Look For

People may enjoy RV travel because they can explore the outdoors while maintaining the comforts of indoor living. Beyond the shelter an RV provides, appliances like a furnace make those outdoor explorations even more enjoyable. But what do you do when you flip on the furnace, and there’s no heat? This is when RV furnace troubleshooting can save the day.

How Does an RV Furnace Work?

The first step in troubleshooting an RV furnace is understanding its fundamental operation.

Using your RV thermostat to turn on the furnace won’t immediately blow warm air into your rig. This is by design. It’s actually a safety measure to prevent noxious gases from entering your rig. 

When turning on the thermostat, several things happen in rapid succession. Let’s take it in slow motion: 

First of all the furnace fan kicks on. The fan both blows air around inside the RV and sometimes forces air through the exhaust pipe. With the fan running it moves a “sail switch” that signifies to the control board that there is airflow. It takes about 15 seconds or so for the control board to sense the airflow and start the ignitor process. It starts the ignitor just before the gas valve opens, allowing propane to flow into the combustion chamber.

The combustion chamber ignites the mixture of propane and oxygen. The ignited combustion chamber heats the air as the heat exchanger pulls in warm air and blows it through the ductwork. 

When the air temperature reaches the thermostat setting, the system stops the heating process until the rig temperature drops. And the cycle starts again. 

➡ Looking for more information? Check out The Beginner’s Guide to RV Furnaces for a full rundown on this essential winter camping appliance.

RV Furnace Diagnostic Lights and Codes for Troubleshooting

When it comes to diagnostic lights and codes on an RV furnace, it’s more important to know what they are and how they work than to memorize specific numbers and letters.

Most newer furnaces have a diagnostic light on the side. The circuit board sends signals much like morse code; the number of blinks identifies the code. A chart somewhere on the furnace should tell you how to interpret the diagnostic lights. 

If there’s an issue with your furnace, the diagnostic light flashes. You then look up the corresponding error code on the chart, which helps you zero in on the exact issue.

Do All RV Furnaces Have a Reset Button?

No, not all RV furnaces have a reset button. In fact, very few of them do. Some RV furnaces will have a reset button on the electrical circuit board on or inside the furnace. Most of the time, however, the furnace is simply reset by turning it off and back on again. The reset button typically does the same thing as cycling power but may be required in the case of a diesel furnace if the fuel has run low.

Pro Tip: Safety is key while RVing. Make sure you know Is It Dangerous To Run Your RV Furnace While Driving before you hit the road.

Common RV Furnace Problems (and How to Troubleshoot)

Numerous problems can arise with an RV furnace. Below, we list the most common RV furnace problems and how to troubleshoot them.

RV Furnace Doesn’t Turn On

If your RV furnace won’t turn on at all, there could be a variety of things going on. If you turn your furnace on and the temperature is below the set point and it doesn’t fire, it’s time to dive into troubleshooting mode. The most common problems are lacking 12V power to the furnace electronics or communication problems between your thermostat and furnace.

How to Troubleshoot

First, verify the furnace has 12V power. Are you plugged in properly to a power source? If not, do your batteries have enough charge? If yes to either of these, it’s time to check fuses.

Go to the DC fuse panel in your RV and find the fuse for the furnace. Pull it out and visually inspect it. If you are unsure, try replacing it or using a multimeter to check continuity.

If the fuse is okay, you will now need to make sure the power is getting to the furnace. Open the furnace and find the wires connecting to it. Use a multimeter set on DC to check for 12V at the power connections. If power is not making it to the furnace, there could be a problem with the wiring that will need further diagnosis by a capable electrical repair person.

If power is making it to the furnace, it may be a communication issue between your thermostat and your furnace. Make sure the wires from the thermostat are connected securely to the furnace while you have it open. This communication could be an ethernet or phone-type port, which will be harder to troubleshoot and will require an electrical professional.

Now go to the thermostat in the wall inside your camper. Remove it from the wall and check the wiring connections. If the thermostat is digital, the screen should be powered on to indicate it is getting power. If it is not getting power, then the thermostat could be bad or there is a problem with the wiring.

The Fan Runs, but There’s No Heat

Usually, if your furnace blower fan turns on but no heat comes out, you’re dealing with a fuel, voltage, ignition, airflow, sail switch, or circuit board issue.

How to Troubleshoot

Fuel: First thing check your fuel supply. Make sure your propane is turned on and has pressure. You can check for pressure by turning on your stove or another appliance that uses propane. This is one of the most common causes for a furnace not to ignite.

Battery Voltage: The blower fan can operate on low battery power, but the combustion chamber can’t ignite if the voltage is too low for the fan to initiate the sail switch. Typically, if your RV battery dips to 10.5 volts, the furnace won’t operate. Recharging the battery is usually enough to regain adequate voltage. 

Pro Tip: Install an RV battery monitor in your camper to monitor your voltage and prevent discharging your battery too low.

Air blows cold but RV furnace doesn't light

Airflow: Another common problem is insufficient airflow, usually from a blockage in the air intake. Things that can block your air intake include leaves, bugs, or other critters, nests, or debris. Cleaning out the intake is the quick fix to this issue. Regularly cleaning the air intake is also a good habit for regular furnace maintenance.

Sail Switch: A failed sail or limit switch is another common culprit, as are corroded or loose fittings. Other issues include a failing gas valve, too much or too little pressure in the propane tank, or a failing ignition control circuit board. Some of these are quick fixes, while others might require professional repair. 

Ignitor: You should be able to hear the furnace ignitor clicking away when attempting to ignite the fuel. If you do not hear the clicking of the ignitor it’s possible there is a problem with the ignition circuit. First, check the sail switch as mentioned above, then take a look at the high-voltage ignitor circuit. You can usually check the relay for the ignitor at the circuit board and see if it’s supplying power when it starts up. If so, but the ignitor is not firing, it’s possible you have a bad ignitor coil.

Did You Know? An RV propane regulator helps control your propane tank’s pressure.

The Furnace Stops and Starts

If the furnace constantly stops and starts when it shouldn’t, there are two common reasons: a faulty thermostat or an issue with the environment around your thermostat. If warm air hits the thermostat directly, the device will register the desired room temperature and shut off, even though it’s only warm in that one spot.

How to Troubleshoot

If the thermostat is faulty, just replace it. New devices are affordable, and as long as you replace it with an identical model, you probably won’t need a technician. When removing the old thermostat, take pictures of all the connections so you can reconnect the new wires in the same order.

A duct register pointing at the thermostat could cause it to shut off prematurely. Redirecting the register away from the thermostat should help. 

You might see the same issue if the thermostat is near a window or door with a leaky seal. Other areas of the house can also run warm, and a thermostat placed too close could cause room temperature problems. For example, your refrigerator or oven can generate heat that affects your thermostat settings. 

Pro Tip: Turn on your RV ceiling fan (or install a new one!) to help circulate warm air throughout your RV in the winter.

If possible, move your thermostat away from the warmer areas of your RV. 

Thermostat at Set Temperature, But Furnace Doesn’t Shut Off

If the RV has reached the desired temperature but the furnace fails to shut off, the thermostat will request more heat from your furnace. This can create rather balmy conditions in your rig. 

How to Troubleshoot

To troubleshoot this RV furnace problem, use a multimeter to check the voltage from the thermostat to the time delay switch. If voltage is present, the thermostat has failed. If there is no voltage, there’s a short somewhere in the system.

➡ We always keep a multimeter in our RV took kit. Find out what other tools we carry here: 36 Important Tools You Need In Your RV Tool Kit

You can check the fuse box in your RV. Your RV fuse box is a big black cover usually under a cabinet or stairwell. When you open it, you should see lots of fuses and labels. The RV furnace fuse should be labeled, otherwise consult your RV owner’s manual.

If the fuse was blown, just replace it, and things should go back to normal. If there’s a short, you can try to find it with your multimeter. Replace any faulty fuses and splice shorted wires. Depending on the situation and your comfort level with wiring, you might need professional help. 

Note that when the furnace reaches the desired temperature, the blower fan will continue to operate for a short time to bring the furnace temperature down. This is a safety factor that’s part of normal operation.

Furnace Not Working on Battery (vs. Shore Power)

An RV furnace should operate solely on 12-volt battery power. If it fails to work on battery power but still operates when plugged into shore power or while a generator runs, the battery is either not charged, failing, or corroded at the connections.

➡ What’s the difference between 12-volt battery power and shore power? Find out here: How Are RVs Wired? Helpful RV Electrical Basics for Beginners

How to Troubleshoot

Check to see if the voltage on the battery is below 12 volts. You shouldn’t discharge a lead-acid battery below 12 volts, as this causes battery damage. Charge the battery to full capacity, and the furnace should be working again.

If your battery won’t accept a charge or it drops in voltage immediately after charging, you probably have a faulty battery. Most auto supply stores will test your battery for free. If it fails the test, it’s time for a new battery.

Pro Tip: Installing reliable lithium-ion house batteries will decrease incidences of RV battery failure.

Do Lithium Batteries Work In Cold Weather? Testing Lithium Vs Lead Acid in Freezing Temps

Check for battery corrosion at least once a month. If you see corrosion on the posts, disconnect the cables–negative cable first–and then clean the posts and connectors. You can buy cleaners explicitly made for battery terminals or make your own. 

A mixture of 1/4 cup baking soda and 1-1/2 cups water sprayed on the posts and connectors should break down the corrosion. Let it sit for a few minutes, then rinse it with plain water.

Weak Air Flow Through Vents

Weak airflow through vents is either caused by a blockage, holes, or loose fittings.

How to Troubleshoot

Checking the air intake for debris is a good place to start when troubleshooting this RV furnace issue. If all is clear there, check the ends of the ducts to make sure they’re snugly connected. Finally, follow along the duct, checking for holes or tears. If you find any, use aluminum tape to repair them.

Removing, Cleaning, and Inspecting Our RV Furnace

Note that many furnaces will not operate without the exterior cover. So double-check the cover is in place any time you’re checking for airflow or other operations.

Furnace Fan Makes Loud Noises

Fan noise is generally caused by a fan blade rubbing against the fan housing. Debris or even lint build-up could be the culprit. The fan motor could also make noise because of a loose or bad bearing.

How to Troubleshoot

First, check for any debris or lint in the fan housing; clean out anything you find. This is also a good time to put a few drops of light viscosity grease on the fan motor shaft right next to the motor. Spin the fan blades by hand and listen. If the noise is gone, you’ve solved the problem.

Pro Tip: Consider investing in an RV vacuum to minimize dirt, dust, and debris in your rig.

If there’s still noise, check the fan housing to make sure it didn’t rattle a screw loose. If this is the case, it may be as simple as tightening the screw so that the housing no longer rubs on the fan blades.

Once you’ve tried the first couple steps, if the fan is still making a squealing or grinding noise, you likely have a loose or bad bearing. At this point, it may be time for a new fan motor.

When Should You Call a Repair Service?

Most of the time, a handy do-it-yourselfer can troubleshoot RV furnace problems and perform many repairs. But there are times when calling a professional is the best and safest option.

If you notice soot on the exhaust vent, it’s time to call in the pros. Soot is an indication that there’s a combustion problem, which can be extremely dangerous and cause a fire. It can also cause carbon monoxide–an odorless gas that’s deadly if inhaled. 

Regularly test your carbon monoxide detectors and watch for soot in the exhaust vent to prevent this. If you detect carbon monoxide or see soot on your external exhaust vent or elsewhere on your furnace, immediately shut it down and have a professional technician inspect it.

RV Furnace Troubleshooting:

The shelter of an RV and the added comfort of an RV furnace can make your travels extremely enjoyable. It’s much easier to explore the outdoors, particularly in the chillier months, when you know you can return to your rig and warm up in minutes.

However, anyone who has traveled for any amount of time in an RV knows that there are no guarantees that everything will go smoothly.

This is especially true for an appliance with several integrated parts, like an RV furnace. But with the troubleshooting tips you just learned, your RV furnace should operate for long periods with fewer instances of trouble.

And even if you do have issues, you soon will be more capable of returning your RV furnace to full functionality and staving off a chilly night in your rig.

Another appliance RVers commonly need to repair is the refrigerator. Learn how to fix your RV fridge here: RV Fridge Not Getting Cold? Try These Troubleshooting Tricks

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