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RV Furnace Troubleshooting: Common Problems to Look For

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. 

Dometic RV Thermostat
When you turn on your thermostat, your furnace goes through a series of internal processes before you feel warm air blowing.

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. 

RV furnace troubleshooting
This is an example of an RV furnace installed in a truck camper.

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.

Furnace Circuit Board
The circuit board inside your furnace will signal the diagnostic light if there’s a problem.

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.

The Fan Runs, but There’s No Heat

Usually, if the blower fan turns on but no heat comes out, you’re dealing with a fuel, ignition 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 ignight.

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 Siwtch: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 its 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 its supplying power when it starts up. If so, but the ignitor is not firing, its 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.

Troubleshooting RV Furnace Thermostat
A faulty thermostat could be the culprit if your furnace constantly stops and starts.

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. 

RV oven with door open
Appliances like ovens can affect your thermostat, especially if they are located in close proximity to one another.

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 rig 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

Troubleshooting RV furnace tripped breaker
Sometimes the problem is a tripped fuse.

You can check the fuse box in your RV. 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.

Battle Born Lithium-Ion Batteries
Furnaces can operate on 12-volt battery power or shore power.

➡ 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
Keep in mind that cold weather when you need the furnace has a big negative effect on battery performance.

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 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.

RV Heat Register and Central Vacuum
Your RV furnace is as susceptible to collecting dust and debris as any other part of your camper.

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. 

RV CO Detector
Make sure you have a CO detector installed in your camper AND make sure it works!

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.

Snow covered fifth wheel
A working furnace will keep you cozy warm all winter long.

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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Tom & Caitlin Morton of Mortons on the Move gave up the stationary life for one where they are constantly on the move. They are full-time travelers, television hosts, and digital media producers.
They left their jobs, sold their house and possessions, and hit the road in September 2015 in their full-time “home on wheels”. Since then they have traveled the US, Canada, and even internationally by RV.
Now, they are Discovery Channel & PBS TV Co-stars of The RVers, producers of “Go North” on Amazon Prime, co-founders and instructors of RV Masterclass, and contributing authors for Hwy.co and an Arizona travel guide.

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Walter E. Bennett

Wednesday 2nd of March 2022

If your furnace is making a loud noise just as it starts, this could be caused by a serious problem called “delayed ignition.” This occurs when unburned oil builds up in the firebox chamber and is ignited all at once. This can be dangerous, and you should call a qualified HVAC specialist immediately.

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