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RV Furnace Not Working? Let’s Troubleshoot!

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.

Is your RV furnace not working? Check out the wiring schematic for an Atwood/Dometic RV furnace. (Diagram and photo credit: Atwood/Dometic)

Wiring diagram of an Atwood/Dometic RV propane furnace. The schematic for a Suburban 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.

Sale
AstroAI Digital Clamp Meter Multimeter 2000 Counts Amp Voltage Tester Auto-ranging with AC/DC Voltage, AC Current, Resistance, Capacitance, Continuity, Live Wire Test, Non-Contact Voltage Detection
  • Versatile Digital Clamp Meter: Accurately measures AC Current (DO NOT MEASURE DC CURRENT)! AC/DC Voltage, Capacitance, Resistance, Diode Continuity...
  • Large Jaw Opening: The jaw opening measures AC current in a conductor without touching or interrupting the circuit. Its slim and compact size makes it...

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 37697 Hydro Flame Replacement Motor
  • RELIABLE - The Atwood 37697 is a The Atwood 37697 is a Hydro Flame replacement motor for Atwood furnaces.
  • COMPATIBILE - Works with furnace models 85-IV 25, 85-IV 31.

Atwood/Dometic combustion wheel:

Atwood 33128 Hydro Flame Combustion Wheel
  • FURNACE PART - Hydro Flame Combustion Wheel
  • TRUSTED BRAND - One of hundreds of Atwood products for furnace solutions.

Atwood/Dometic blower wheel:

Atwood 33126 Blower Wheel
  • Atwood Fantastic Vent Corp. BLOWER WHEEL 8500-III&IV

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:

Suburban 161122 Gas Valve
  • Rig Rite 12/24 Volt Marine Circuit Breaker w/ Auto Reset - 40 Amp

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:

Sale
Suburban 230956 Electrode Assembly
  • package height : 6.35 cm
  • package length : 2.54 cm

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:

Sale

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:

Sale
JCJ M-300 Mud Dauber Screen for RV Furnace Outside Fitting
  • RV furnace and fan unit outside fittings
  • Fits DuoTherm and Suburban

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

Sale
RV Furnace Vent Screen for RV Water Heater Vent Cover, RV Bugs Screen,Flying Insect Screen,Stainless Steel Mesh with Installation Tool
  • 【Package Include】: 1x RV Water Heater Screen( 8.5''x 6''x1.3''), 1x RV Water Heater Screen (4.5" x 4.5" x 1.3") , 2 x RV Furance Screen( 2.8" x...
  • 【RV Insect Screen 8.5" x 6" x 1.3"】 : Compatible with Atwood 6 & 10 Gallon and Suburban 6 Gallon water heater vents. Easy to install: It comes...

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.

Is your RV furnace not working? Maybe the furnace vents on the exterior are blocked?

When the exhaust vents aren’t hot, use a finger to check for soot at the exhaust ports. Soot build-up is a sign of 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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David C

Saturday 3rd of December 2022

Our heater runs fine but when it gets super cold outside it shuts off. if we turn thermostat off and back on it will come back but only run for about four hours and then shut off again. Could the thermostat be faulty?

Jocelyn Antillon

Wednesday 30th of November 2022

Hello, our heater turns on and runs, warms to the desired temperature and cycles properly a few times but in the middle of the night it does not come back on and we have woken up due to being in a very cold RV by about midnight to 2am. If I turn the thermostat off, wait for it to click, and turn back on heat, it will warm up only to stop working again by about 5am (when we wake up freezing). Any input? Thank you!

Stan

Tuesday 20th of December 2022

@TheRVgeeks, Update, now the fan comes on but does not ignite the gas for heat. Currently Heater is not producing heat just cold air.

Stan

Monday 19th of December 2022

@TheRVgeeks, Like Ray, having same issue as Jocelyn however, I'm directly connected to power. no obstruction in exhaust and flames are blue. Heater will run for a few hours then will cut out. First the blower will run without the furnace trying to ignite, then will auto shut off completely until I cycle the wall power to turn it off and back on. It generally needs to sit off for about 12 hours before starting to heat again but only runs for a couple of hours then the same cycle again.

Ray

Wednesday 14th of December 2022

@TheRVgeeks, Having the same Issue but connected to shore power. also noticed the stove flame has quite a bit of orange in it and the water heater is taking longer than normal to heat up, when looking at the flame on the water heater it there was some carbon build up you could see glowing. Any thoughts or suggestions?

TheRVgeeks

Saturday 3rd of December 2022

HI Jocelyn. Sorry to hear about your issue. Sounds to us like it could be one of a couple of things (not in any particular order):

It could be that your house batteries are getting low/old. In the coldest part of the night, they may not be able to produce enough power to keep the furnace running. The furnace blower is usually a fairly large power draw, so if the batteries are getting weak, combining that with the cold temperatures could do the job and make the furnace not run. Look around for somewhere nearby that you could take your batteries to to have them do a load test on them to determine if they’re losing their ability to store & release energy. Replacing them with new ones may solve the problem. The thermostat could be failing and may need to be replaced. It may be easier to get and install a replacement thermostat (it’s usually just a couple of screws and a modular wire) to see if that does the job. It could also be an issue with the furnace itself… it may have something blocking its outlet, preventing proper airflow for cooling the workings… so, when it gets very cold at night and the furnace has to run longer in order to maintain the interior temperature, it’s overheating. By the time you wake up and notice that it’s gotten cold… the furnace has cooled off again, so toggling the thermostat off and then on again restarts the cycle. Look for mud dauber nests, spider webs, or something else nesting somewhere in the exhaust path for the furnace.

Hope these ideas lead to you finding the solution!

David C

Saturday 3rd of December 2022

@Jocelyn Antillon, Hi Jocelyn, same is happening to us, did you get a reply or resolution?

Abigail Morrison

Saturday 19th of November 2022

I have an sf35 and replaced sail switch. Before setting everything back in place I wanted to make sure it ignited, which it did. Once I got everything back in place I started it again and unfortunately it started doing the same thing as before which was the blower coming on then shutting off without heating. This happened after a power outage a couple weeks ago. Any thoughts would be most appreciated!

James

Wednesday 16th of November 2022

Atwood Model 8940-III DCLP Unit will only ignite and burn when exhaust port is covered. Please help.

TheRVgeeks

Thursday 17th of November 2022

Hi James. Sorry to hear you're having trouble. Without seeing it, and without being professional techs, we're guessing the sail switch or crud blocking the burner are the most likely causes. If you're unsure about it, you should probably try to find a local RV tech to check it out.

Darin Mahlke

Saturday 12th of November 2022

I live full time in my 4 season Grand Design 5th wheel and temps have dipped into the teens consistently at night here in eastern Idaho. I lived in this trailer in Boise Last winter with plenty of nights below freezing without any issues. Here in Idaho Falls it is colder but not by a significant amount. I returned from a work trip tonight to find that my lights went from flicker to not working, the fridge giving me a lo dc alert and not working (on electric or gas), and my furnace kicking on, starting to blow heat and then slowly sputtering out after about 1 -3 minutes.

I’m connected to 50amp shore power which has never given me issues but my batteries are down to 7V from always running at 12. I assume that’s from the cold, as I assume the low DC warning on the fridge is as well. I do have power in my outlets, microwave light, electric fireplace and some of the lights are now operable vs the previous flicker to completely fading out.

I’m completely ignorant to electrical/power systems and would sincerely appreciate some guidance. Should I disconnect batteries via the disconnect switch in passthrough bay? Is there a panel or switch which needs to be insulated or evaluated to cure the low dc power alert? Any feedback on what might be happening and advice would be an incredible help.

Thank You

TheRVgeeks

Sunday 13th of November 2022

Hi Darin. First, sorry to hear about the trouble you're having. From what you've described, we'd say it sounds like your battery(ies) may be dying. It's like in your car... oftentimes you don't realize your car's battery is getting old and needing replacement until the outdoor temps drop and all of a sudden it's having trouble starting, or the windows roll down slowly. The cold definitely slows down battery chemistry... and in an older/weaker battery, it's more noticeable.

If your batteries are a couple years old (flooded lead-acid, we assume), it's likely they need to be replaced. Now, if they're newer than that (and usually last you longer), then it's possible that there's a problem with your onboard converter/charger not re-charging them correctly.

Removing the batteries and having them load/stress tested at a battery dealer may be the way to tell. If the batteries test poorly, replace them. If they test out OK, you may need to begin sleuthing out issues with your converter/charger.

BTW... the fact that your 120V power outlets, microwave (light), electric fireplace and "some light" work is because they operate off of the 120V AC power coming in through your shore power cord. They're not affected by the low/dead battery. Your furnace fan blower, roof vent fans, slideout motor(s), and most of your other lights will be 12V DC, and need the battery to function.

Hope this helps... hit us up with other questions if you have them and we'll see what we can do to assist.

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