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When Your RV Furnace is Not Working, Then What?

Published on December 14th, 2023 by Lucinda Belden

Four-season camping is enjoyable when you’re prepared for cold weather. But if the temperature drops and your RV furnace is not working, you might be tempted to pack up and go home. But before you leave that great campsite, first try these troubleshooting tips. Hopefully one of them will lead to an easy field repair or at-home fix.

Key Takeaways

  • A basic understanding of furnace parts and operations makes it easier to troubleshoot your furnace problem.
  • Most RVers experience one of three common reasons why their RV furnace won’t work.
    Reason 1: The blower fan does not come on when the temperature should trigger it.
    Reason 2: The blower fan does come on, but turns off shortly thereafter.
    Reason 3: Once turned on, the furnace never shuts off.
  • This article explains both novice and advanced level ways to troubleshoot and fix each potential RV furnace malfunction.

Step 1: Get to Know Your RV Furnace Parts

Before you can really understand why your RV furnace is not working, you need to have a basic knowledge of the typical RV furnace setup, and all related parts. Most RV furnaces are propane fueled.  These systems usually consist of these major parts:

Power

Fused, 12-volt power supply

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Fuel

Propane tank supply

Blower Fan

This moves the heated air into the duct or vents to heat the rig. It also supplies air for combustion.

Vents and Ducts

The path the heated air travels into the coach, and often, the underbelly.

Igniter

When it’s time to produce heat, the igniter sparks, causing the propane to ignite. The igniter assy also contains the flame sensor

Controller Circuit Board

Reads input from other sensors, opens, or closes the propane valve, triggers propane ignition, and starts or stops blower operation.

Sail Switch

This small sensor detects the movement of air created by the blower.

High Limit Switch

The RV furnace high limit switch is designed to turn off the burner if the temperature surrounding the combustion chamber becomes too hot. This is a safety feature

Thermostat

This can be analog (physical slide) or digital, where a desired temperature is set, and a signal is sent to the controller to tell it to turn the furnace on or off as the temperature changes to below or above that setting.

Step 2: Understand How Furnace Components Work Together

Your next job is to understand how the individual furnace components work correctly together to heat your RV. Here is a basic step-by-step way in which RV furnace systems work.

  1. The thermostat detects a lower temperature than the desired setting. (We’ll use 60° as an example.)
  2. Thermostat tells the controller to turn on the furnace.
  3. The controller turns on the blower. Then the blower fan pushes the heated air through the ducting along with air for combustion.
  4. The sail switch confirms to the controller that air is moving. This safety feature confirms the combustion chamber has been purged and that air is being supplied for combustion.
  5. The controller opens the propane valve to the ignition chamber.
  6. The controller triggers the ignition device to light the propane.The thermal sensor (which is part of the igniter assembly) tells the controller that there is now heat.
  7. The rig begins to heat up. When the thermostat detects the desired 60° temperature, it tells the controller to turn off the furnace.
  8. The controller closes the propane valve and the flame ceases.
  9. The blower may continue to run for an additional time to move the remaining heated air through the ducts, cool down the device and ensure any unspent propane is exhausted through the outside vents.

This is the ideal scenario of a working RV furnace. These various steps, while somewhat simplified, explain how all the pieces work together. 

We have a 2019 Jayco Northpoint. Our furnace was working, this morning it was putting out cool air, not hot. Any thoughts?

Furnace Not Heating, @Patti, Jayco Owners Forums

The Three Most Common Reasons Why an RV Furnace Won’t Work

When an RV furnace is broken, it’s usually caused by one of two common scenarios. Let’s look at each.

Scenario 1: The blower fan does not come on when the temperature should trigger it.

A blown 12v fuse to the furnace power
Dead or very drained batteries
Loss of shore power
One or more loose wires
Loss of shore power
A seized motor or motor shaft
The controller board has gone bad
A bad thermostat might also be the problem

Important: Whether air is moving or not is very important.

If there is no movement, then the heat and flame sit in one place instead of passing through the ducting. If this happens, the entire furnace unit, the housing and anything surrounding it could get excessively hot and possibly cause a fire.

Also, If there is no air movement the sail switch won’t engage, which prevents ignition. If ignition somehow still occurred, the limit switch would cut power to the board / gas valve. Combustion would be shut down before the furnace becomes too hot

Scenario 2: The blower fan does come on, but turns off shortly thereafter, and has only pushed cold air through the vents before turning off.

The propane supply has run out so no flame can be made. (This can, and most likely will occur during an on-cycle, causing the furnace to shut off prematurely.)
The igniter is misaligned or malfunctioning and not lighting the propane
The sail switch is bad and did not detect air current or did not signal to the controller that it detected it.
The high limit switch has gone bad and isn’t opening when the area surrounding the combustion chamber becomes too hot.
One or more of the ducts has a blockage and is creating additional heat buildup in the system, triggering the thermal sensor too early. In this scenario, if you are able to feel cold air initially, you would sense some warm air before the limit switch opens. Plus, the fan would continue to run until the limit switch cooled and closed, starting the ignition cycle again.

Here’s one possibility: The controller has gone bad and isn’t performing one or more of these responsibilities:

  • opening the propane valve
  • triggering ignition
  • reading the sail switch confirmation
  • reading the thermal sensor confirmation

Scenario 3: Once turned on, the furnace never shuts off.

If this happens, it could mean that:

  • The thermostat isn’t reading the correct temperature, so its not telling the controller the desired temperature has been reached.
  • The outside temperature is cold enough that the furnace simply cannot heat the entire area enough to reach the intended temperature.

This possibility can be problematic. You will run out of propane much faster. And your rig can reach a temperature higher than you anticipated.

A situation where the ambient temperature never reaches the intended setting can be tricky. While it’s important to keep the furnace running to prevent your Pex RV water lines from freezing, the constant operation of the unit will quickly burn through your propane.  Once you’re out, you may have no way to heat the rig, especially if you’re boondocking. 

Can RV Heat Pumps replace your broken RV furnace?

While an air conditioning unit that also has a heat pump can keep you from freezing during the cold temperatures, it most likely cannot send heat to the RV’s underbelly where the water lines are located. This is because most A/C units are located on the roof of the rig.

My furnace is not working. When the thermostat is set to FURN, nothing happens; no blower, no clicking, nothing. The gas is on and the stove lights, the thermostat is set to the correct mode and the temperature is set high enough for the furnace to come on. The 12v fuse is good. I have reset the breaker on the furnace and checked for loose wires.

I am trying to determine whether the problem lies with the furnace or the thermostat. According to the wiring diagram, the blue wires are from the thermostat. How can I test to see if the start signal from the thermostat is reaching the furnace?

RV Furnace is Not Working, @RonaldC303, AirForums

How to Troubleshoot Your RV Furnace Problem

Whatever potential issue you are facing, there are some debugging steps to go through. Some are easy and some that are more difficult.  Let’s start with the easiest troubleshooting steps.

Check Your RV Batteries’ Charge

RV battery monitor readouts for troubleshooting when an RV furnace is not working
Ensure your batteries have ample power for their type.

This is easy enough if you have a battery monitor. For lithium batteries, the monitor usually indicates a percentage of capacity.  For non-lithium, you’ll need to be familiar with the voltages that indicate your level of charge. Turn to the battery manufacturer for the most accurate specifications of your batteries.

While a healthy, fully charged lead acid battery might read between 12.3 Volts and 12.6 Volts at rest depending on charge level (with 12.6 being fully charged), these levels are different for modern lithium batteries!

Let’s have a look at 12Vlithium iron phosphate batteries, such as the Renogy lifepo4 battery, often used in solar applications. A fully charged 12V lithium iron phosphate battery should read between 13.4 Volts and 13.6 Volts at rest. However, it’s worth noting that these readings may vary depending on the specific manufacturer and model of the battery.

What Should A 12 Volt Battery Read When Fully Charged? Renogy

Check Your Furnace Fuse

12-volt RV fuse panel
Check the 12v fuse in the fuse panel.

Another easy check. Just pull the fuse and look for a burned-out or solid element.  Optionally, if you are comfortable performing basic electronics, you can use a voltmeter to check for continuity on the fuse itself. 

You may also be able to check the fuse panel itself for a 12-volt feed on the incoming side of the fuse socket (positive) with a good ground (negative) available.

Check Your Propane

Propane safety gauge example
Check your propane tank levels.

If you have a gauge on the tank connection, look to see if you’re in the green or in the red. But if you don’t have one of these, and you have removable, portable tanks, you might need to close the valve, disconnect it, loosen the straps, and check the weight.

Keep in mind that the furnace problem might also be caused by too low of gas pressure caused by a faulty regulator or something like a propane leak.

I have a 2021 Crossroads Sunset Trail Super Lite. My furnace will not fire up. It was working fine and now want ignite to produce any heat. What can I do to troubleshoot.

RV Furnace Not Firing, @chuck31 Crossroads Owners Forums

Advanced Ways to Troubleshoot an RV Furance

If none of these debugging steps revealed an easy fix, it’s time to move on to the more complex RV furnace troubleshooting. 

The best way to find out why your RV furnace is not working is by having the right tools and spare parts. Many RVers carry extra parts for not the time when not if but when an RV furnace is not working. Having extra parts on-hand, before you have a problem is very helpful. Carrying extras of these components can make the difference between a warm, cozy night in the cold, versus freezing in your rig or having burst water lines.

You can learn to test the parts described below by reviewing the Do It Yourself RV article “how to Test RV Furnace Components.

Many of the components in your furnace are the same as in your hot water heater, refrigerator, and AC systems. Therefore, many of the same tests would apply and can help you in troubleshooting and repairing these systems.

How to Test RV Furnace Components,” Do It Yourself RV

When removing your furnace from the rig for testing and parts replacement, consult your RV service center and/or RV furnace appliance manuals. If you don’t have a copy, just search the web to locate your specific furnace model’s user manual.

Before performing any of these steps, turn off any propane supply and pull the fuse for the furnace.

Troubleshooting Task 1: Check for loose wires between components and controller board 

RV furnace wiring
RV furnace wiring

If you’re getting into the furnace compartment, be sure that each wire is connected to their intended locations. There can be a lot of wires.

Troubleshooting Task 2. Is Your Sail Switch Bad?

RV furnace not working sail switch
The most common issue is a bad sail switch.

A bad RV furnace sail switch is usually somewhat easy to replace. The cost for doing so can range anywhere from $10 to $20. Get a sail switch that is compatible with your furnace make and model.

On some furnace types they are very accessible since it is indeed a common failure. Other furnace units may have the sail switch located in an accessible, but hard to reach spot. RV furnace sail switches come in various shapes and colors, but a general design is pictured above.

Troubleshooting Task 3: Check the Limit Switch

RV Furnace limit switch
Is your limit switch bad?

Different furnace models may have this located in different places on the furnace. The limit switch is another component that’s easy to test and replace. They range in price from $5 to $20. A limit switch is made of metal.

Troubleshooting Task 4: Test your RV Propane Furnace Igniter

Suburban 525009 (232286) OEM RV Suburban Furnace Igniter Electrode Assembly
Suburban 525009 (232286) OEM RV Suburban Furnace Igniter Electrode Assembly

If you can’t achieve a spark, you can’t have heat. An RV furnace igniter like the one shown above is often in a less accessible location. Replacement will most likely require you to remove the furnace unit out of its housing. Igniters can be purchased for $10 to $20.

Troubleshooting Task 5: Test the Control Board

Troubleshooting an RV furnace control board.
An RV furnace control board.

This is the more expensive option should it need replacing. Depending on the model or age of your RV furnace, you may be able to buy a direct replacement from the manufacturer. Or, replacement could require you to obtain a similar board type from an after-market vendor.  The price of an RV furnace control board can range anywhere between $50 to $100 or more.

RV Furnace Troubleshooting Summary

As you can see, there are a few ways to uncover why your RV furnace is not working. Depending on your level of expertise with testing, replacing, and troubleshooting, the diagnosis and actual RV furnace repair can vary.  Doing it yourself requires you to feel comfortable with the task and the amount of work required to get it running again. 

If all else fails when your RV furnace is not working, go to an RV service center. Just be prepared for a wait. You can also call a mobile RV technician in your area. Keep in mind that RV furnace parts may be hard or slow to obtain. A smart RV purchases the correct RV furnace replacement parts ahead of time, which practically guarantees that your winter camping nights will be as warm as you’d like them.

This post may contain affiliate links or mention our own products, please check out our disclosure policy here.

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