RV Furnace Troubleshooting Tips

Your furnace is excellent when it keeps your RV warm on cool summer nights or helps you extend your camping season into the early spring or late fall. But you’ll need these RV furnace troubleshooting tips when it doesn’t work as anticipated. 

There’s nothing quite worse than waking up in the middle of the night to realize your furnace isn’t working – I’ve been there more times than I’d care for. While you can always supplement your furnace with a space heater for RV use, but these will only heat the living space and not the underneath compartments or belly pan where your plumbing is located. So, you eventually need to figure out why your furnace isn’t working.

Technician Tip: Always play it safe when troubleshooting gas RV appliances. When in doubt, contact an RV furnace professional. Consult the owner’s manual for your furnace for model-specific troubleshooting tips. 

What Is Normal RV Furnace Operation?

Let’s begin by defining what’s “normal” in the operation of an RV furnace. Learning how RV furnaces work will give you the background to troubleshoot more efficiently when the need arises. 

Starting out, you must have propane, it must be connected to your furnace, and the valve on the top of your propane container(s) must be completely open. Then, you must turn the furnace on and adjust the thermostat to a setting higher than the ambient air temperature inside your RV.

When you’ve completed those steps, the following sequence occurs when your RV is functioning properly:  

• The fan turns on first
• Within 5-10 seconds, you should hear the click of the igniter followed by the sound of the burner being lit
• Another 5-10 seconds later, you should feel warm air coming from the furnace vent(s)

Quick Safety Tip: Check the outside furnace vent for the free flow of exhaust gases.

RV Furnace Troubleshooting For When It’s “Not Normal”

Again, your owner’s manual is your best source for RV furnace troubleshooting advice. However, the four most common issues that RVers experience when their furnace isn’t working are:

1. Nothing happens when I turn on my furnace
2. The blower turns on, but my furnace does not ignite
3. The furnace cycles frequently
4. The furnace doesn’t shut off

Let’s cover the potential causes and troubleshooting paths you can take for each of these common issues. 

1: Nothing happens when I turn my furnace on

You’ve confirmed your furnace is turned on, but nothing is happening.

The first potential cause is your thermostat is simply set too low.

Adjust the thermostat setting to a temperature that’s higher than the ambient temperature inside your RV, and listen for the fan to commence blowing. If not? 

The next potential cause is low battery voltage. 

To eliminate low battery voltage as a potential cause, you can: 

• Check battery connections for corrosion (recommended at least once a month)
• Check battery levels
• Recharge the battery if the output is below 12 volts

A third potential cause is a blown fuse.

To check this, inspect the 12-volt DC fuse in your RV’s distribution panel. If blown, replace it with one of the same size and type. However, if a fuse blows, something has caused it to blow. It’s important to find out what caused the fuse to blow before continuing, which is where you may need the assistance of a certified RV technician.

2: The blower turns on, but my furnace does not ignite

You’ve turned your furnace on and adjusted the thermostat as recommended above. The blower motor comes on to power the fan, but no ignition occurs. 

The first potential cause to investigate is a lack of propane.

This could be caused by an insufficient propane supply or a closed propane valve on top of your container(s). 

Take the following steps to investigate this potential cause: 

• Turn off the furnace
• Check your propane container levels
• Ensure the tank valve is completely open
• Turn on the furnace and adjust the thermostat to retest

If propane supply isn’t the issue?

The next potential cause is air built up in the propane supply line.

This can happen between uses when the propane supply is shut off at the container valves.

To check and/or remedy this issue: 

• Turn off the furnace
• Turn on a gas appliance that’s located closer to the fuel source (i.e., your stovetop or water heater)
• Allow that appliance to run for five to ten seconds to fill the line with gas
• Shut off and retest the furnace

Still not getting ignition?

The next potential cause is insufficient airflow. 

Follow these steps to check that your RV furnace is getting enough airflow for safe burning ignition: 

• Turn off the furnace
• Check the air intake on the exterior of your RV
• Clean it out if blocked with leaves, dirt, or other debris

Now that you’ve eliminated propane supply, air buildup, and insufficient airflow, what’s next?

Another potential cause of a furnace failing to ignite is a broken ignitor.

To check your ignitor’s condition, ask yourself the following question: 

• Do you hear the click of the ignitor after the blower has been running for 5-10 seconds?

If yes:

The ignitor is good, and you may have another cause (i.e. no propane or air in propane lines).

If no: 

The ignitor may be bad. But before jumping to that conclusion, it’s worth checking the sail switch and the high-voltage ignitor circuit. If the ignitor relay on the circuit board is supplying power, you may have a bad ignitor coil. 

But here’s where we start to require the expertise of a certified RV technician. Why?

The final potential causes of a failure to ignite are a failing sail or high limit switch, a failing gas valve, or a failing ignitor control circuit board.

With all these potential causes, your safest action is to contact your nearest RV service center or a mobile RV mechanic to schedule a full furnace diagnostic.

3: My furnace cycles frequently

Your furnace is turning on and blowing hot air, but it’s cycling on and off more frequently than it should – or at least more frequently than in the past. 

The easiest potential cause of a frequently cycling furnace is drafts coming from worn door or window seals. 

Cool air from leaky windows and doors can cause your thermostat to cycle on more frequently than necessary. Check the seals around all doors and windows near the thermostat to eliminate drafts. 

Ensure there are no rugs or blankets covering the floor registers or an ice chest or suitcase blocking the return air vent as these will restrict airflow and overheat the furnace resulting in short cycling.

Additionally, if the furnace duct is misaligned and pointing towards your thermostat, warm air will rise around the thermostat and cause it to shut off even if the rest of your RV is below its temperature setting. Check the furnace duct position and realign if necessary.

Finally, try turning on a vent fan or the fan function on your A/C unit to circulate air more evenly through your RV.

The next potential cause is a faulty thermostat. 

To check your thermostat’s operation:  

• Check the voltage from the thermostat to the time delay switch. If voltage is present, the thermostat has failed. 

The remedy for this issue is to replace the thermostat with an identical model. Lucky for you, we have a comprehensive tutorial to help you with an RV thermostat replacement.

• If voltage isn’t present, you may have an electrical short in the system.

You can also check your RV’s fuse box. 

• If the fuse is blown, replace it with one of the same size and type and retest.
• If the fuse isn’t blown, you may have a shorted wire or faulty fuse.

If you’re worried about an electrical short or a faulty fuse, your safety course of action is to consult a certified RV technician.

4: The furnace doesn’t shut off

Your furnace doesn’t have any issue turning on and producing heated air, but it’s not shutting off (which is a major safety red flag!). 

The likely potential cause is a faulty thermostat. 

To check your thermostat’s operation:  

• Check the voltage from the thermostat to the time delay switch. If voltage is present, the thermostat has failed. If voltage isn’t present, you may have an electrical short in the system.

Additionally, you can check the fuse box on your RV’s distribution panel. 

• If the fuse is blown, replace it with one of the same size and type and retest.
• If the fuse isn’t blown, you may have a shorted wire or faulty fuse.

If you’ve exhausted these troubleshooting tips and you’re worried about an electrical short or a faulty fuse, your safety course of action is to consult a certified RV technician.

Proper maintenance is vital to your furnace’s continued operation. In addition to knowing how your furnace works and understanding these troubleshooting tips, read our guide to keeping your furnace in good working order to add the recommended procedures to your periodic RV maintenance calendar. Here are additional resources:

• How Does a Tankless Water Heater Work in an RV?
• RV AC Dripping Water Inside?
• RV Water Heater Troubleshooting

Are you experiencing other furnace issues, or do you have questions about these troubleshooting tips? Let us know in the comments below.