RV Furnace Not Working? Let’s Troubleshoot!

If your RV furnace isn’t working, there are a number of possibilities as to the reasons why. Depending on the symptoms your furnace is experiencing, you can troubleshoot a non-working RV furnace on your own. This post aims to help you with that process.

We’re going to be focusing here on the most typical RV furnace, the propane furnace. Hydronic heat (HydroHot, AquaHot, Oasis) is a different breed of RV furnace, and we’re not covering those here. This post assumes you’ve got a typical propane RV furnace.

An important safety note: Your RV furnace uses both propane and electricity, both of which can potentially pose a danger. If you’re not comfortable dealing with propane or electricity, call in a professional for anything other than the most basic of these troubleshooting ideas.

Let’s get to it!

How Does an RV Furnace Work?

An RV propane furnace is a forced-hot-air system that requires a thermostat, a control board, a relay, a blower motor, sail switch, high-level switch, ignitor, and some ductwork.

A traditional RV propane furnace uses both propane and electricity (12V DC from the battery(ies) in your RV). The propane burns to create hot air while the electricity powers the electronics & circuits (in both the furnace and thermostat) and run the fans.

To make the system work, you set the thermostat higher than the RV’s current inside air temperature, which triggers the furnace to activate the blower motor. Ultimately, if the system functions correctly, the propane ignites, creating hot air that’s distributed throughout the RV through the ducts.

That’s the nutshell version. For a closer look at each of the steps involved in the operation of an RV propane furnace and the parts required for it, see our detailed post explaining how an RV propane furnace works.

What Are RV Furnace Diagnostic Codes?

Furnace diagnostic codes can assist you in determining if something has gone awry, keeping the system from working properly.

Newer RV furnaces will have a diagnostic light. The circuit board sends signals that illuminate the diagnostic light with a number of flashes representing a particular code (similar to Morse code).

A chart in the owner’s manual (or sometimes on a sticker on the furnace itself) identifies the meaning of each code, allowing you to interpret the information offered by the diagnostic lights.

So, you’ll note the number of flashes from the light, and then look up the meaning using the corresponding code in your owner’s manual or on the sticker on the furnace. With that information, you’re on your way to fixing the problem.

Typical RV Furnace Wiring Diagram

To get started with your troubleshooting, it will be helpful to understand how your furnace is wired. This is a diagram of a typical Atwood/Dometic RV furnace. The diagram for a Suburban RV furnace would be similar.

The Most Common Reasons Why an RV Furnace Is Not Working and How to Troubleshoot Them

There could be a number of reasons why your furnace doesn’t produce heat when you turn up the thermostat in your RV.

Let’s take a look at the most common issues and how to troubleshoot them.

You Turn Up Your RV’s Thermostat and Nothing Happens

When you turn up your RV’s thermostat, within a few seconds you should hear a fan kick on. If you turn up your RV’s thermostat and nothing happens at all, then your fan/blower motor isn’t starting. A non-functioning fan/blower motor could have a number of causes.

Inadequate Power Supply

A traditional RV propane furnace requires a strong 12V power supply for various furnace components to operate. If your furnace doesn’t kick on at all (meaning you never even hear the fan come on) this could be due to low battery voltage.

The first thing you’ll want to do is check your 12V power supply to make sure you have adequate 12V power to run the furnace. If you have a dead house battery, for example, the furnace won’t be able to function.

Confirm that you have a strong 12V power supply coming from your RV’s batteries, and then check the connections along the wire running from the thermostat to the furnace’s circuit board.

You can use a multimeter like this one to check for adequate 12V power.

Relay for the Blower Motor is Bad

Another reason why your furnace fan may not be kicking on involves the relay on the circuit board. If the relay isn’t opening, the blower/fan can’t start. In this case, you can troubleshoot by testing the relay.

To do this, you’ll bypass the relay to see if the fan will run on the direct power from the battery. If the fan functions using direct power, then you know that the fan is good and the problem is likely to be the relay.

However, if the fan doesn’t run on battery power, this indicates that your relay is likely okay but the fan itself is problematic (or stuck… if it’s been a while since you last used your furnace, it could be seized from rust).

Note that if you’re hearing a squealing sound from your RV furnace, this is likely a blower motor that needs to be replaced.

Here’s a look at the components of the blower – the motor, combustion wheel, and blower wheel:

Atwood/Dometic blower motor:

Atwood/Dometic combustion wheel:

Atwood/Dometic blower wheel:

My RV Furnace Fan Runs But There’s No Heat

If you turn up your RV’s thermostat and in a few seconds you hear the fan kick on but it’s blowing cold air that doesn’t warm up, you could have any one of a number of problems, most of which you may be able to address yourself.

Fuel (Propane) Source

The number one reason behind a furnace that’s not supplying heat is your fuel source. The most obvious issue, and the first one to check, is your propane supply. Make sure you have adequate propane to run your RV’s furnace.

If you don’t have a gauge handy, you can check your tank level without a gauge.

Or Peter can walk you through the process in our YouTube video on how to check your propane tank without a gauge:

You’ll also want to make sure your propane tank valve is open (did you close it when you stored your RV?), and your onboard propane regulator hasn’t failed or clogged. See our post for more information on RV propane regulators.

Sail Switch Failure

Another common reason for an RV furnace that’s running, but isn’t producing heat, is the failure of the sail switch to open. The sail switch is one of two safety switches in your RV furnace, and if it doesn’t open your RV furnace won’t produce heat.

The sail switch itself can fail over time, or it can simply be clogged with debris such as dust, pet hair, insect nests, or rust. In some cases, the sail switch may be able to be blown clean and continue to work properly. In others, it will need to be replaced.

You can find detailed information on the sail switch in our post: “What Is an RV Furnace Sail Switch?”

Here’s an example of a sail switch:

Bad Gas Valve

If your RV’s furnace fan runs but the furnace isn’t producing heat, you may also have a bad gas valve.

Take a seat near the exhaust port of your RV’s furnace while someone else works the thermostat to trigger the furnace to come on. When you fire up your RV furnace you should hear the fan turn on, then the solenoid should make a clicking sound. Next you should hear a rapid ticking sound (the ignitor), and then you should smell propane gas.

However, if your RV furnace’s fan turns on and you hear the click of the solenoids and then the rapid ticking sound, but you do NOT smell propane, you’ve likely got an issue with your furnace’s gas valve.

Here’s an example of a gas valve for a Suburban RV furnace:

Failure of the Ignitor

Next in line in the furnace lighting process is the ignitor, so let’s troubleshoot that element.

Once again, seated at the exhaust port of your RV’s furnace, listen carefully to what happens when the thermostat is turned up inside your RV.

You should hear the fan turn on followed by the click of the solenoid. Next you will either hear the rapid ticking or no ticking at all. If you DO smell LP gas at this stage of the process but your RV furnace doesn’t ignite, the problem may well be the ignitor.

Instructions for how to test the ignitor can be found in our post, “My RV Furnace Fan Runs But There’s No Heat”.

A Suburban RV furnace ignitor looks like this:

Faulty Control Board

And finally, if your RV furnace runs but there’s no heat, there could be an issue with the control board. This is essentially the brain of the RV furnace. Power needs to get TO the control board and also travel THROUGH the control board to the other components of the furnace.

Here again, if your RV furnace runs but there’s no heat and you suspect a faulty control board, visit our post for instructions on how to test the board.

An RV furnace control board:

Your RV Furnace Ignites and Produces Heat But Shuts Off Prematurely

If you turn up your thermostat, your RV’s furnace starts properly and is producing heat, but then shuts off on its own prior to reaching the temperature you’ve set, there are a couple of issues to troubleshoot.

High-Level Switch

The high-level switch (sometimes referred to as a high-limit switch) is the second of two safety switches in your RV’s propane furnace.

It’s the job of the high-level/high-limit switch to shut down the furnace if the temperature in the combustion chamber reaches a certain temperature. This excess heat can be caused by a leak in one of the combustion chamber tubes or by the improper exhausting of the hot air (which could be due to low voltage causing the exhaust fan to run too slowly or by some other failure in the exhaust system).

To address this, make sure that the exhaust is not blocked (by dust, dirt, debris, insect nests, etc.), and that there is proper airflow (check for anything that could be blocking/slowing the air intake for the furnace inside your RV).

You can also check the tubes in the combustion chamber for damage such as holes or cracks.

Should you find no issues after doing all of this, then your high-level switch may be bad. You can test your high-level switch with a multimeter.

This is a high-level (or high-limit) switch:

NOTE: Bear in mind that if you intend to order parts to repair your RV furnace, it’s imperative that you first confirm that the part is the correct part for your make/model.

Flame Sensor

The flame sensor is a critical safety component on your RV propane furnace. When the propane gas is ignited, the heat causes the flame sensor to produce a current of electricity.

However, if the flame in the combustion chamber of your RV’s propane furnace goes out, it will shut down the furnace completely. This occurs so that gas doesn’t continue flowing if it isn’t being combusted.

So, if your furnace ignites and begins to produce heat but then shuts off, the issue could be the flame sensor. The flame sensor is generally part of the ignitor assembly.

What Else Could Cause an RV Furnace to Not Work?

There are a couple of additional easy things to check if your RV furnace isn’t working properly.

Outside Exhaust Vent Blocked or Dirty

It’s important for the furnace’s exhaust port to be free of debris in order for the furnace to ignite and operate normally. Sometimes mud daubers, spiders, or other insects make their way inside from the exterior exhaust port and build nests that create a host of furnace issues.

Removing the exhaust housing and checking for nests and other debris and cleaning the area completely may help.

To prevent this from happening in the first place, installing screens can be extremely helpful.

This is the type that fits the furnace exhaust ports of our RV and may fit yours as well:

You can also purchase a kit like this one with a variety of screens for this and other exhaust ports on your RV:

Air Return Grill Blocked or Dirty

RV furnaces often experience long periods of no use and some are used only occasionally, if ever.

Always inspect your RV’s airreturn grill (and behind it) for dust, pet hair, dirt, and obstructions prior to using the furnace. Be sure nothing is blocking the fresh air return while you’re using the furnace. Keep items away from the return grill while the furnace is in use.

Incomplete Combustion

If your RV’s furnace isn’t working properly, carefully check the exhaust vent for soot. The presence of soot indicates incomplete combustion.

Make sure to check the exhaust vent only when the vent isn’t hot. Using a finger, check for black soot in and around the exhaust vent.

Should you find black soot in this area, don’t operate the furnace because incomplete combustion can expose you to dangerous carbon monoxide gas. Have your RV furnace inspected by a qualified technician ASAP.

Have You Experienced Issues With Your RV Furnace Not Working?

As always, we’d love to hear from you about any issues you may have experienced with your RV’s furnace and how you resolved them.

And it bears repeating that while it’s good to be able to narrow down what the issue could be using basic troubleshooting methods, RV furnaces can pose significant dangers due to the fact that they use both propane and electricity.

If you have any doubt about your ability to properly troubleshoot and/or repair your RV’s propane furnace, be sure to call a professional to avoid these dangers.

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