RV Furnace Troubleshooting How To Fix Common Issues

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Last Updated on August 23, 2024 by Paul Clayton

RV Furnace Troubleshooting How To Fix Common Issues

You’ve been out and about all day and the temperature is dropping. You turn the dial on the thermostat, expecting a rush of warm air, but nothing happens. You’re in the middle of nowhere, everyone is wearing jumpers, and the temperature is set to plummet overnight.

What are you going to do? It’s time for a bit of RV troubleshooting. This is a horrible situation to find yourself in, but all is not lost; with a little bit of knowing how, it’s possible you can get the furnace back up and running within a few minutes. We’ll cover some common issues and how to fix them in this article, but to start with, we’ll get ourselves familiar with how an RV furnace works and the parts that make it work

How Does an RV Furnace Work?

This video has been included to clarify the topic. Credit goes to Camping World Tutorials

‘Video is not the main content of the page’

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We can’t account for every model and furnace type, but this applies to the most common RV furnaces.

1. The thermostat triggers a request for heat, sending a current to the RV furnace.
2. The current powers the time delay relay, which passes power to the RV furnace blower.
3. The blower spins up and pulls air from the Air Return, creating airflow through the heat exchanger and out of the ducts. Another fan pulls air into the combustion chamber to feed the furnace.
4. The fan air caused the sail switch to close as the blower speed increased.
5. Power flows through the High Limit Switch and to the Control Circuit Board.
6. The gas supply opens as power is delivered to the control board, causing the DSI igniter to spark.
7. The gas lights create heat within the combustion chamber.
8. Heat will pass into the heat exchanger, heating the air and passing it through the ducts.
9. The Thermostat will reach its preconfigured temperature as the RV begins to warm up.
10. The power is removed once the correct temperature is reached, and the burner shuts down.
11. The fab will continue to run to cool the furnace safely until the time delay switch opens.

If you own a furnace that operates a pilot light, the operation is similar, but the control board doesn’t trigger the ignitor. Once the pilot light is lit, the gas flow controls the furnace.

All RV furnaces operate on battery power alone, so you don’t need to plug into the mains or run a generator. As long as the RV’s batteries are suitably charged and you have a gas supply, you can operate the furnace with no issues.

RV Furnace Parts

Air Return: The air return is a vent on the inside of the RV that sucks in air to circulate through the heat exchanger and out through the ducts. This is not to be confused with the air used for combustion; there is a separate intake for this.

Blower Motor: The motor drives a couple of fans that circulate air through the furnace. One fan brings air in through the Air Return, and the other brings air in from outside into the combustion chamber and out through the exhaust.

On/Off Switch & Circuit Breaker: The circuit breaker and On/Off Switch interrupt power to the blower motor. The on/off switch is commonly used for servicing, while the circuit breaker can automatically shut down in case of an issue.

If the circuit breaker has triggered, it can often be reset, but the underlying cause of the trigger should be investigated and fixed.

Combustion Air Intake: The air inlet on the RV’s exterior pumps air into the combustion chamber.

Combustion Chamber: The chamber where oxygen and propane are burned to produce heat.

DSI: The DSI is an acronym (Direct Spart Ignition). An electronic igniter uses a spark to ignite the gas-air mix.

Ducts: The Ducts carry the heated air from the furnace to the interior of the RV.

Exhaust: The exhaust is an air outlet on the RV’s exterior that exhausts the gases produced during combustion. The gases are a combination of carbon dioxide and carbon monoxide. These gases must never enter the interior of the RV; doing so can result in serious injury or death.

Fan Speed Controller: The Fan Speed Controller controls the speed of the fans, increasing or decreasing the BTU output of the furnace. Lower fan speed will result in a lower BTU output.

Heat Exchanger: The heat exchanger uses conduction to take the heat generated within the combustion chamber and warm the air circulating through the ducts.

Gas Valve: The gas valve is an electronically controlled valve that opens to allow gas to flow into the combustion chamber. The circuit board controls it.

High Limit Switch: The high limit switch controls excess heat from damaging the heat exchanger. The switch cuts power and avoids damage if the temperatures get too high. Damage to the heat exchanger can cause deadly gases to enter the ducts, an essential safety device.

Igniter: The igniter generates a spark to ignite the propane. In a DSI furnace, the igniter replaces a pilot light. It will also act as a sensor to verify that ignition was successful.

Ignition Control Circuit Board: The ignition circuit board operates the gas valve and fires the ignitor spark. In some models, the ignitor will try several times to ignite the furnace; you may hear a distinct tick-tick-tick sound as the spark initiates. Some models may only attempt to ignite every 60 seconds, while others will attempt once and then shut down if the ignition is not achieved. These require the thermostat to be cycled to try again.

Pilot Light: The pilot light produces a small flame that continuously burns and will light the primary propane source when the valve is opened. This is not present in DSI furnaces.

Sail Switch: The sail switch features a paddle arm that covers the blower air stream. As the blower reaches full speed, the sail switch is pushed out of the way, allowing power to be passed to the ignition switch.

Thermostat: The thermostat monitors the internal temperature inside the RV and will trigger the furnace to turn on if the internal temperature has not met the specified threshold.

Time Delay Relay: The delay is slightly delayed before initiating the furnace cycle.

RV Furnace Troubleshooting General Tips

Tools

The voltmeter is the most important tool in your arsenal for troubleshooting an RV furnace. Having one and knowing how to use it will help you diagnose and fix most RV furnace issues.

We would use the voltmeter to ensure sufficient power reaches the components that make up the RV furnace. You don’t need to go out and buy an expensive voltmeter; a cheap one will usually suffice.  [

Diagnostic Codes and Lights

Newer RV furnaces tend to have a small LED attached to the ICB. This LED will flash several times if an issue is present; the number of flashes will indicate the type of issue. A chart will be available somewhere on the surface to help you decipher what the flashes indicate.

Fans and Blower Motors

The furnace fans are most often located behind the outside access cover. The motor will provide power through a shaft to the main furnace fan and the combustion air fan. Typically, the motor and fans are covered in a case containing the sail switch.

The RV’s 12v power system will power the motor. If the RV is plugged into shore power or has a generator running, the battery will remain fully charged, and there should be no drop in the motor voltage. However, if the RV battery is at the end of its life or has been powering the motor for an extended period, the voltage may not be sufficient to power the motor.

Wear and tear or corrosion of the wiring may also impact the voltage reaching the motor, so checking the voltage at the batteries and the motor may help diagnose some issues.

Combustion Exhaust and Air Intake

The external combustion exhaust and air intake are at the external furnace cover panel. Bugs, dirt, or even nesting mice can block airflow and inhibit operation, so it’s worthwhile checking for blockages.

Word of warning: some furnaces will not operate with the external cover removed, so ensure to replace it after checking for blockages.

Air Return and Ducts

All air vents should be kept as clean and dust-free as possible. The intake vents should be cleaned periodically to remove dirt buildup and ensure air flow. Dirt that enters the ducting can build up on fans, switches, and the heat exchanger, which can affect performance or cause a fire risk.

Resets and Lockouts

Some furnaces will enter a lockout condition if an issue is encountered. It simply 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 to a value that would not cause the furnace to turn on.

Wait approximately 30 seconds, then turn the thermostat back on and increase the temperature to the desired level.

Gas Pressure

All gas appliances are set to operate with a standard supply pressure of approximately 3psi. The pressure within a propane tank is much higher than this, so a propane regulator controls the gas pressure. A residue in the propane tank can interfere with the regulator, causing it to fail or work intermittently.

An empty tank will also not provide any pressure, so check your levels.

If you suspect an issue with the gas supply, a gas regulator is the most likely component to fail. Thankfully, they are inexpensive and can be easily replaced. Check out our article on the best RV propane regulators.

Common RV Furnace Problems

RV Furnace Blower Won’t Start

Several reasons can cause this:

1. Not enough power from the thermostat to the furnace. It can be caused by a bad wire or power not reaching the thermostat.
2. Failed Time Delay Relay
3. There is no power from the RV battery to the furnace relay switch.
4. The circuit breaker is triggered or turned off for servicing.
5. Loose wiring.
6. Failed blower motor.

Low RV battery voltage can cause a spike in the current, which may trigger the circuit breaker. Additionally, excessive strain on the motor caused by dirt can trigger the circuit breaker. If the motor is short, the breaker can also trigger.

Check the wiring, looking for corrosion or loose wires. Check for a buildup of dirt around the fans and the motor. Check the voltage coming from the battery and where it reaches the motor. Reset the circuit breaker and try again.

RV Furnace Fan Runs But No Heat

This is one of the most common issues you’ll encounter, but it’s also one of the most straightforward troubleshooting.

1. The Sail Switch fails to close fully, providing no power to the rest of the furnace. A stuck or faulty sail switch can cause this, or the fan turns too slowly to push the sail. The motor might be slow due to a lack of voltage, so check the voltage at the batteries and the fan. The motor may also turn slowly due to corrosion or dirt. Lastly, a blockage at the air return will cause a lack of airflow.
2. If the high-limit switch is not closed or has failed, no power will reach the controller circuit board. Check the voltage at the controller board and the switch.
3. The controller circuit board has failed, and the gas valve is not opening or triggering the ignition. Check the voltage at the gas valve during the turn-on cycle.
4. The gas valve is not opening, so no gas reaches the combustion chamber. This can be caused by a failed valve or a lack of power. Check the voltage at the gas valve.
5. The gas valve opens, but no propane flows. A line blockage, a bad regulator, or a lack of pressure can cause this. Check other gas appliances to ensure they are working.
6. The igniter is not sparking, and the pilot light is not on. It can be caused by a defective igniter or a lack of power. Check the voltage at the igniter and the gap between the igniter to ensure it’s not too large or short.
7. The furnace lights, but the igniter fails to detect a flame and initiates a shutdown.
8. Both propane and spares are used, but the burner still fails to light. This can happen if the air intake is blocked or insufficient airflow into the combustion chamber.
9. Corroded or loose fittings in any of the components listed above.

RV Furnace Runs Once But Won’t Restart

This issue is most often caused by a blockage in the air intake or exhaust, which causes a lack of air in the combustion chamber. Check for debris, dirt, or bugs in the exhaust or inlet. It can also be caused by a lack of gas pressure or a partially opening valve.

RV Furnace Stops and Starts

This issue is often caused by the thermostat receiving false readings. Hot air from the duct is blowing on the thermostat, causing it to think the RV is warmer than it is, or cold air is blowing across the thermostat, resulting in a similar issue. If the ducts can be directed, ensure they point away from the thermostat. Also, check for any drafts.

If the issue persists, the thermostat is likely faulty and should be replaced.

RV Burner Goes off and On

This problem is called ‘cycling on the limit switch’ and is a symptom of the heat exchanger overheating, which causes the high limit switch to act. Nine times out of ten, this is caused by a lack of air circulation through the furnace, generally due to a blockage of some sort.

A build-up of dust or dirt within the heat exchanger can also cause this problem; in some circumstances, a faulty limit switch can also cause it.

The RV Furnace Doesn’t Shut off When the Temperature is Reached

This problem would indicate that the thermostat is still requesting more heat. You should check the voltage from the thermostat and the time delay switch. If a voltage is present, then the thermostat is faulty. If no voltage is present, there’s likely a short somewhere creating the voltage that usually comes from the thermostat.

It should be noted that the fan typically runs for a couple of minutes after the required temperature is reached, cooling the furnace safely.

RV Soot on the Exhaust Vent

Soot indicates that combustion is not occurring cleanly. Carbon monoxide is another product produced during improper combustion, and it is a severe and dangerous gas. If you see soot on your external exhaust, you need to get the furnace inspected by a professional immediately. You MUST NOT use the furnace until it’s been inspected.

Soot and carbon monoxide are produced when no oxygen is available during the burn, usually caused by a blocked intake or fan not turning fast enough.

RV Furnace Works on Shore Power but not on Battery

If your RV furnace only works when you’re connected to mains power or a generator, it’s a sign that your battery needs replacing or that there’s corrosion. These issues result in reduced voltage reaching the furnace and a lack of power to the motor.

RV Furnace Stops Running Overnight

The most common cause of this problem is an exhausted battery. The furnace motor uses a lot of electricity, and if the battery or batteries are not up to spec, they may drain overnight.

In addition, corrosion of wiring can cause excessive current draw from the battery, resulting in the battery losing power faster than expected, so it’s worth checking

RV Furnace Fan Making a Noise

This issue is most likely caused by the fan blades rubbing against the fan housing; a loose or bad bearing within the fan motor may also cause it.

Weak Air Flow From RV Furnace

We often see this issue with ducts that are excessively long or have crimps somewhere. Check as many ducts as possible, straightening or removing excess ducts. It’s also worth checking the outlets; many have adjustable airflow, so removing the cover will allow you to check.

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