Why Is My Furnace Not Working in My RV?

Written by Jeff Campbell in RV Troubleshooting,RV Appliances

When traveling in your RV, it’s important to have a working heater. Unfortunately, it’s usually on a cold night when we find ourselves asking why is my furnace not working in my RV?

Here’s what I’ve learned from living in mine:

As a general rule, RV furnaces usually stop working because of insufficient battery voltage or dirty air filters. So check the air filters, and ensure shore power or a generator are providing power. Or if boondocking, ensure the batteries are charged and the inverter is on. 

There are a couple of other reasons why your RV furnace is not functioning as it should and having a general idea of how your RV furnace works will make troubleshooting issues much easier.

In this article, we’re diving deep into RV furnaces. We’ll talk about how RV furnaces work and troubleshoot common problems, like blowing cold air, how to light it, and how to test it.

RVs are great, but there’s always something new to learn, even for the most experienced RV owners.

Why is my furnace in my camper blowing cold air?

Common reasons for camper furnaces blowing cold air are low battery voltage or a dirty filter. If the voltage is too low, the fan will operate, but the gas valves will not open. Dirty filters will restrict air flow, causing the heat exchanger to overheat and shut off too quickly.

With the furnace in your home, the blower doesn’t start until the plenum is warmed up.

The plenum is an air distribution box attached to the supply outlet of the HVAC equipment. It is what’s responsible for heating or cooling the air to make your house comfortable.

In an RV, the furnace starts running immediately.

That’s because it uses the same motor to power the hot-air blower and the blower that moves air through the combustion area. If the batteries are too weak to power both blowers, the sail switch will not light. If it is already lit, it will shut off.

So, if the house batteries are weak, the blower motor spins.

But it doesn’t spin fast enough to trigger the sail switch. As a result, you get a furnace that blows cold air. If the blower is blowing, and the sail switch is triggered, but the furnace is still blowing cold air, it could be due to a dirty air filter.

Dirty air filters are the most common cause of furnace problems.

Dust and dirt restrict airflow. If the airflow is restricted too much, the heat exchanger will cut off. If the blower is running, but cold air is coming out, try replacing the filter.

If you turn your heating unit on and feel warm air for a moment and then feels cold, it could be the flame sensor. If the flame sensor is dirty, your gas burner won’t stay lit. This will cause the air to go cold shortly after the furnace is turned on.

This can also occur when the house batteries are weak. The blower motor spins, but not fast enough to deflect the sail switch. This results in a furnace that blows cold air.

How does an RV furnace work?

An RV thermostat indicates to the blower to turn. The motor will run for 15-30 seconds, then the pilot light or direct spark will ignite the burner to heat the air. After that, the blower propels warm air into your RV. 

Understanding how your furnace works is vital to diagnosing problems.

The furnace should turn off in the reverse order after reaching the set temperature. To troubleshoot a problem with your RV furnace, you have to first rule out simpler problems.

But to rule out simpler problems, you need to know the general mechanics. I can’t account for every model and furnace type, but most common RV furnaces will work similarly.

They will all work something like this:

  1. The thermostat triggers a request for heat, sending a current to the RV furnace.
  2. The electricity powers the time delay relay, which in turn passes power to the RV furnace blower. source
  3. The blower spins up and pulls air from the air return, creating a flow of air through the heat exchanger and out of the ducts. Another fan pulls air into the combustion chamber to feed the furnace.
  4. The blower speed increases, then the fan air causes the sail switch to close.
  5. Power then flows through the High Limit Switch and onwards to the Control Circuit Board.
  6. Power is delivered to the control board, it opens the gas supply and causes the DSI igniter to spark.
  7. The gas lights and creates heat within the combustion chamber.
  8. Heat will pass into the heat exchanger, heating the air passing through the Ducts.
  9. The RV begins to warm up, then the thermostat will reach its pre-configured temperature.
  10. Once the correct temperature is reached, power is removed, the burner will shut down.
  11. The fan will continue to run in order to cool the furnace safely until the time delay switch opens.

If you’re like me, you like to see how things work. Words simply aren’t enough. There is an excellent video that shows how RV furnaces work on the bottom part of this article.

Furnaces with pilot lights operate in a similar fashion, but the control board doesn’t trigger the ignitor. Once the pilot light is lit, the furnace is controlled by the flow of gas alone.

All RV furnaces operate on battery power.

You don’t need to plug into the mains or run a generator. As long as the RV batteries are suitably charged, and you have gas, you can operate the furnace with no issues.

How do I test or reset my RV furnace?

The reset button is located inside the blower compartment on the side of the motor. It is usually labeled, and sometimes red. Turn off the power supply and the gas to your furnace. If the reset button is up, push it to reset your furnace. You can also pull the fuse, wait a few minutes, and reinsert the fuse.

There are a few different ways to reset your furnace.

You may have to go as far as switching off the power and the gas and then turning it all back on before you do a reset. If that’s the case, you may have to press and hold the reset button for 30 seconds. For a more exact way to reset your furnace, consult the manual for your furnace.

How to test your furnace with basic tools

First, and most important, is a voltmeter. Having a voltmeter and knowing how to use it will help diagnose and fix most RV furnace issues. Use the voltmeter to ensure that sufficient power is reaching the components that make up the RV furnace. You don’t need anything fancy.

A cheap one will usually get the job done.

Newer RV furnaces will usually have a small LED attached to the ICB. If there is a problem, the LED will flash. The number of flashes will point to the type of issue. There should be a chart nearby to help you decipher the codes that the flashes indicate.

Typically, fans are located just behind the access cover. The motor provides power through a shaft to both the main furnace fan and the combustion fan. They are usually covered in a protective case that may also contain the sail switch.

The RV’s 12-volt power system will power the motor.

If the RV is plugged into shore power or has a generator running, there should be no drop in voltage to the motor. But if the RV battery is weak, the voltage may not be enough to power the motor.

Wear and tear or corrosion of the wiring may impact the voltage as well. Checking voltage at the batteries, as well as at the motor, may help diagnose some issues.

Airflow issues with your RV heater

You should also check the external combustion exhaust and air intake.

These are located at the external furnace cover panel. Bugs, dirt, and nests can block airflow, inhibiting operation. Be sure to replace the cover after checking for blockages. Some furnaces will not operate with the external cover removed.

Dirt that gets into ducts and air vents can restrict flow. Dirt in ducts can also build-up on the heat exchanger, which can affect performance or even be a risk for fire.

Some furnaces will enter a lockout condition if an issue is encountered. This means the control board won’t allow the furnace to start. The lockout condition can be reset by turning the thermostat off and reducing the temperature, so the furnace doesn’t turn on. Wait approximately 30 seconds, turn the thermostat back on and increase the temperature to the desired level.

All gas appliances are set to operate with a standard supply pressure of approximately 3 PSI.

The pressure within a propane tank is much higher than this, so a propane regulator is used to control the gas pressure. If a residue is present in the propane tank, this can interfere with the regulator, causing it to fail or work intermittently.

Additionally, an empty tank will not provide any pressure, so be sure to check your levels.

If you suspect an issue with the gas supply, then a gas regulator is the most likely component to fail. Thankfully they are inexpensive and can be easily replaced.

Will my RV furnace work without a battery?

An RV furnace will work without a battery when connected either shore power or when using a generator. But when not connected to those power sources, RV furnaces will require battery power. And even with one of those, it will still need propane.

All RV furnaces operate on battery power.

You don’t need to plug into the mains or run a generator. As long as the RV batteries are suitably charged, and you have gas, you can operate the furnace with no issues.

Most things in your RV need a properly functioning 12-volt DC house battery system. That is where your RV’s power converter is used. When plugged into shore power, the converter is converting 120 volt AC power into 12 volt DC power.

Furnaces don’t rely solely on electricity, either. They also need propane. So, you can bypass the need for a battery by hooking up to 110 power. But it still uses propane.

Your best bet for a properly functioning furnace is through your converter or good, fully charged batteries.

If you own a Class A motorhome and are considering living in it full-time, there are some things you want to keep in mind.

You want to consider the temperatures, the amount of snow and ice, as well as how insulated your RV is.

But there is a lot more to living in a Class A motorhome than that. Just read this recent article to learn more about living in a Class A motorhome in the winter.

Just click the link to read it on my site.

Does my RV furnace have a pilot light?

Old RV furnace systems mostly have pilot lights while most newer RV furnaces have replaced the pilot light with a direct spark ignition system. This means they have electric ignitions, and there is no need for a pilot light.

So unless you have an older RV, just make sure your propane is turned on, and the thermostat is adjusted properly.

The chances are that your RV does not have a pilot light or it has an automatic pilot light. Many new RV furnaces have replaced the pilot light with direct spark ignition or an automatic ignition system.

If your furnace is having a hard time keeping the pilot light lit, check the thermocouple to make sure it’s positioned correctly. A malfunctioning regulator on your propane tank could also cause an irregular pilot light.

First, make sure the main propane valve for your RV is turned on. The main shutoff valve is usually located at the propane tank.

To turn on the furnace, just use the thermostat. Make sure it’s set to heat and adjust it as necessary, just like you would at home. The furnace should automatically kick on and off to maintain the proper temperature.

If it does have a pilot light, make sure the propane tank is on, turn your fan to auto, and turn your thermostat to the highest heat setting. Let the fan run for a few minutes.

Next, remove the access panel and remove the cover.

Turn your gas dial to the pilot position and hold down the knob. Then, light the pilot. Press the striker ignition device several times, or use a lighter or a match. Release the knob, and turn it to the “on” position.

Set the thermostat to the desired position.

RV propane furnace troubleshooting tips

Dirty air filters are the most common cause of furnace problems. Dust and dirt restrict airflow. If the airflow is restricted too much, the heat exchanger will cut off, but the blower will continue to run, blowing out cold air.

While some issues can be resolved with these tips, not everything can be fixed. If your furnace still isn’t working, even after troubleshooting, it may be time to call a professional.

The first thing you want to do is take off the cover and get a look inside. Look for anything amiss, debris, or anything that could be blocking the exhaust.

Also, verify the intake is open and ventilated. Blow out any dust and debris from the assembly using pressurized air. Clean off the grate, and make sure there is nothing covering it. Clean out any debris the pressurized air missed.

If your furnace is blowing cold air, try turning the heat off and back on. If the air feels warm and then turns cold, it may be that the flame sensor is dirty. If the flame sensor is dirty, the burner won’t stay lit. This causes the air to go cold soon after the furnace is turned on.

If the flame sensor is clean, check your air filters.

Dust and dirt restrict airflow. If the airflow is restricted too much, the heat exchanger will cut off. If the blower is running, but cold air is coming out, try replacing the filter. Be mindful of the outside temperature.

If it’s a particularly cold day or night, your heat pump might just be blowing air that’s cooler than your body temperature, making you think it’s cold. But as it gets colder and your heat pump can’t pull as much heat in from the outdoor air, the air coming from your vents drops slightly in temperature. source

Check the battery. There should be a minimum of 10.5 volts coming into the unit. Check to make sure power is coming into the RV. Check all of the fuses. Check the thermostat to make sure it’s not damaged, and check to make sure the tubing that delivers the heat to the vents are not kinked or bent, obstructing airflow.

Check your propane levels. It could be that the furnace blower can start, but if you don’t have enough gas, the burner won’t ignite. Also, check to make sure your propane is turned on. If your furnace does have a pilot light, look inside and make sure it’s staying on.

If none of these things work, it’s time to consider calling a professional. The issue could lie within the furnace assembly.

Another note: If you see soot on the outside of your RV near the exhaust vent, this is a sign that there is improper combustion. It’s not normal to see soot on your exhaust vent.

RV Furnace Heating System Troubleshooting Tips and Guide | The Savvy Campers

Did I answer everything you wanted to know about why your furnace isn’t working?

I covered a lot of ground in this article!

If your furnace is blowing cold air, fixing it could be as easy as changing out the filter, but you may need to check your propane and battery power, too.

I’ve provided a troubleshooting guide to get you through most situations. If you haven’t found your fix yet, it’s probably time to consult a professional.

Jeff Campbell

Jeff Campbell travels on and off with his 3 daughters in a Newmar Baystar Class A Motorhome. He writes extensively on both RVs, campgrounds, parenting on the road tips, remote learning & schooling, and much more!

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