Common Furnace Error Codes (Lennox, Carrier, York, Rheem, Nordyne)

Furnace codes are invaluable during the troubleshooting of heating systems. If you know how to read the codes correctly, you can cross-reference with your owner’s manual to determine why your furnace is misbehaving. 

To this end, we’ve rounded up all the important codes from the leading furnace manufacturers, so you know where to start whenever you run into a problem with your furnace.  

Carrier Furnace Codes

Carrier is among the top HVAC brands in Canada and North America and offers a wide range of highly efficient furnaces. The following are the common error codes to help you with troubleshooting whenever you run into a problem. 

  • Code 1-1: This is shown when stored status codes are erased since power is interrupted.
  • Code 1-2: Signals blower ON after power-up. It means that the blower has to run for some seconds when the unit is powered up during a call for heat.
  • Code 1-3: Indicates that a limit flame switch problem that normally auto-resets after 3 hours. 
  • Code 1-4: Represents an ignition problem. However, the furnace will auto-reset after some hours.
  • Code 2-1: This is a sign of gas heating lockout. You need to check if the gas valve wiring is correct.
  • Code 2-2: Signals an abnormal flame sensing process. You should check for a leaky gas valve that can result from a gas valve stuck open.
  • Code 2-3: Signals a pressure switch problem. To correct this issue, you should check if the pressure switch is stuck or obstructed.
  • Code 2-4: Indicates that the secondary voltage fuse is open. This often results from short-circuiting in the secondary voltage wiring.
  • Code 3-1: This means you have a blocked vent switch. Common causes are inadequate combustion air supply, a defective pressure switch, vent issues, and a defective inducer motor.
  • Code 3-3: Says the flame roll-out switch is open. You most likely have a faulty switch, inadequate combustion air supply, loose blower wheel, or a dirty filter.
  • Code 3-4: Signals an ignition problem. To fix the issue, troubleshoot the furnace for low inlet gas pressure, a defective gas valve, low flame carryover, rough ignition, or an ungrounded flame sensor.

Lennox Furnace Error Codes

Lennox furnaces have two LED lights that flash in different patterns depending on the underlying issue. The LED lights can also light continuously or blink slowly or fast, depending on the issue. You need to know how to read them to correctly troubleshoot the ongoing problem. 

For instance, if both LEDs are concurrently flashing slowly, it means that the furnace is working normally – but there’s no call for heat, i.e., your furnace isn’t heating your home. However, if both are flashing quickly, the operation is normal, and there is a call for heat, i.e., it’s heating your home. 

The following are several other codes and what they represent;

  • If the first light is blinking slowly and the other one blinking rapidly, it indicates that your furnace has low voltage.
  • If the first LED light is flashing rapidly and the other one is blinking slowly, it signals that your furnace has incorrect wiring.
  • If the first light is lighting continuously and the other one is flickering slowly, it shows that the flame roll-out switch is likely not operating well.
  • If both LED lights are not lit, your furnace is not working because it is not receiving power.
  • If the pair of lights are blinking slowly, it means that the furnace’s blower motor is not operating correctly.

York Furnace Error Codes

Like other furnaces, York models have various ways to signal different errors. The furnaces typically have a built-in light-emitting diode (LED) located behind a transparent cover in the lower door of the furnace. 

In addition, the flashing LEDs on your furnace will communicate a specific fault code that appears on the diagnostic chart. 

These error codes are seen in three different colors, i.e., red, green, and amber (or yellow). The following is a summary of what each color and the different color combinations represent, depending on the number of flashes. 

Red Flashes

  • One red flash: One red flash signals that a flame is present, but the gas valve isn’t getting power. 
  • Two red flashes: Show that the pressure switch is stuck in the closed position. This can be caused by low pressure or incorrect wiring of the pressure switch.
  • Three red flashes: Are a sign that the pressure switch is stuck in the open position. This can be caused by a blocked air intake pipe, blocked vent pipes, or faulty combustion air blower.  
  • Four red flashes: This indicates that the high-limit switch is open. The cause could be a dirty air filter, a faulty blower motor, or restricted circulating airflow.

Green Flashes

  • One flash: Indicates normal operation with no call for heat.
  • Two and three flashes: Indicate that there are no error codes stored in the memory system.
  • A rapid green flash: Is used during factory testing.

Amber Flashes 

  • One amber flash: Indicates regular operation with a call for cooling.
  • Two amber flashes: Are a sign of regular operation with a call for heating.
  • Three amber flashes: Signal regular operation hence ending the cycle of the furnace burner.

Trane Furnace Error Codes

If you are a Trane furnace user, you should know that you own one of the best furnaces today. Trane furnaces are reliable, high-performing, and long-lasting. Moreover, the company provides exemplary customer support. 

However, before you dial the customer support line, you should try decoding the onboard error codes to see if you can fix the problem yourself. The flashing LEDs correspond to a specific fault code shown on a diagnostic chart. 

The following are the main codes to get you started with the troubleshooting process;

  • The lights are flashing slowly: This indicates that the furnace is operating normally, but there’s no call for heat.
  • The lights are flashing fast: This signals that the furnace is operating normally and calling for heat, i.e., heating your home. 
  • Lights are OFF: If the lights are off, it means the furnace isn’t getting power. This may point to a wiring problem, PCB issues, or a power blackout. 
  • Two flashes: Check for incorrect wiring or a clogged pilot tube. Clean the pilot orifice and if the issue doesn’t resolve, call an HVAC expert. 
  • Three flashes: The pressure switch is having a problem. Perhaps the draft inducer motor has malfunctioned, or the pressure switch is bad. 
  • There are four flashes: Signals an open high limit switch. You need to check the thermal protection system.
  • Five flashes: This means that the flame has been sensed where no flame should be present, i.e., a flame roll-out. 

Rheem Furnace Error Codes

Rheem furnaces have integrated controls that flash a warning LED light when there is a problem with operation. An `OK’ LED light on the control board blinks a code that indicates the underlying problem. As long as you can count the number of light flashes, you can easily find out the underlying issue. 

So, what do the various number of flashes mean?

  • One flash

One flash of the light with a two-second pause between the flashes indicates a lockout for an hour. A Rheem furnace cannot run when the lockout is in progress, no matter how hard you try. 

A failed ignition sequence causes this lockout problem. Unfortunately, a problem experienced during the ignition sequence constitutes a safety hazard. So, DIY is out of the equation. Instead, you need to call an HVAC expert. 

  • Two flashes

Two flashes of the LED light are a sign that the pressure switch is open. Rheem furnaces are manufactured uniquely with default pressure settings. If the pressure level doesn’t rise to the setting, the switch will remain open. Thus, the furnace cannot run. 

An open pressure switch may point to a bad furnace inducer motor, a bad pressure switch hose, an electrical circuit issue, or a defective switch.  

  • Three or four flashes

Three LED flashes indicate that the high limit switch is closed at the start of the heating process. Remember that the limit switch prevents the furnace from overheating, such as in the event of flame roll-out. 

If the light blinks four times, the pressure switch is closed when it should be open. The switch is likely stuck closed, perhaps because of an electrical malfunction. 

Also, check if the furnace control board has no light

Goodman Furnace Error Codes

Goodman furnaces have many error codes. We’ll only focus on the codes for the most common errors. 

  • One LED flash, constantly ON: Signals that your furnace is not operating normally. You should check if the thermostat is connected correctly.
  • One LED flash which blinks on and off: Means that the furnace has locked out because of too many ignition attempts. You need to reset it manually. 
  • Two LED flashes: Indicate the draft inducer motor isn’t functioning correctly. Alternatively, your furnace needs pressure switch replacement.
  • Three LED flashes: The furnace has a closed pressure switch circuit that transfers electric current when it shouldn’t. You should check the wiring.
  • Four LED flashes: Show that your furnace has a primary open circuit. This calls for filter checking and cleaning and tightening loose wires.
  • Five LED flashes: Indicate that your furnace can sense a flame, but there’s no call for heat. 
  • Seven LED flashes: Are a warning of a low flame sensor amp reading due to low gas pressure. You need to adjust the gas pressure using information from the manufacturer. Otherwise, turn off the furnace and find out if you have a gas leak.
  • Eight LED flashes: Indicate that your furnace has a defective ignitor, which needs to be replaced. Also, check the wiring for proper connections.
  • Nine LED flashes: Warns you that your furnace has a high-stage pressure switch that won’t close during a high-stage induced draft blower operation.
  • Continuous LED Flashes: Are a warning that your furnace has reversed polarity or higher voltage due to incorrect wiring.

American Standard Furnace Error Codes

Whereas most furnaces use error codes to communicate various operation errors, American Standard uses what are known as flash codes instead.

The furnaces feature a red LED light that constantly blinks. If it’s blinking steadily and continuously, the furnace is running normally and doesn’t require intervention. However, if it begins to flash in patterns, something is amiss. 

The number of flashes between breaks will give you a hint of the underlying issue. Below is a summary of the most common flash codes and what they mean.  

  • Two flashes: Two flashes show that the furnace is likely to blow cold air because of the dropping flame. Causes of a dropping flame include a bad gas valve, low gas pressure, and blocked burners. 
  • Three flashes: Three flashes are a sign that the pressure switch has a problem. It may be operating when it shouldn’t.
  • Four flashes: Signal a problem with the limit switch. Is the limit switch stuck? Is it open when it should be closed?
  • Six flashes: Indicate a polarity problem. Your furnace is likely experiencing reversed polarity.  
  • Seven flashes: Indicate a problem with the gas valve. Is the valve faulty? Is it leaking gas? Is it blocked?
  • Nine flashes: Signal an ignition problem. This might be because of incorrect wiring or a defective igniter. 
  • Twenty-two flashes: Indicate a problem with the flame itself. You might have a low flame sense signal due to low gas pressure.

Nodryne Furnace Codes 

The LED light on the Nordyn furnace has many functions. It indicates the state or mode in which the burner is operating. It also signals fault and helps determine the underlying issue. The following are common codes and what they mean;

  • LED lights normally to the end: If the LED light comes on when you start the furnace and stays on for the rest of the heating operation, everything is fine.
  • Flashing quickly: If the LED flashes quickly, i.e., On ½ second and Off 1/2 second, it’s in lockout state or restricted mode. To exit the lockout state, press the reset button. 
  • Flashing slowly: If the furnace flashes slowly, i.e., ON for two seconds, then OFF for two seconds, it’s in the recycle state. It means that it stopped trying to sense the flame after a lockout timer expired. The furnace returns to an idle state after 60 seconds. 

Arcoaire Furnace Codes

Arcoaire furnaces use a combination of flashing LED lights and codes to alert you about potential issues with your furnace. The most common codes are as follows;

  • Error codes 12 and 44: Indicate that the blower calibration has a problem that needs to be addressed.
  • Error code 13: This shows that the limit switch has tripped. The good news is that the problem auto-resolves after three hours. 
  • Error code 14: This is all about an ignition problem. Perhaps the system isn’t getting gas, or the ignitor doesn’t work. 
  • Error code 41: This indicates that the blower isn’t running at the required revolutions per minute.
  • Error code 43:  This informs you that the pressure switch has a problem.
  • Error code 45: The furnace will be flashing yellow, showing that polarity has reversed. To fix this problem, you need to do proper polarity testing.

Additional error codes on Arcoair furnaces include;

  • Red LED1 ON: This indicates that the furnace is operating in emergency heat.
  • Red LED2 ON: This means that the microprocessor has a problem.
  • Yellow LED3 ON: The furnace is operating under high heat.
  • Green LED4 ON: Furnace is functioning in low heat.
  • Red LED2 flashing: Line voltage polarity reversed.

Coleman Furnace Error Codes

Coleman makes excellent furnaces known for durability and reliability. The furnaces are also typically quiet and very efficient (98% AFUE or higher). If you ever run into a problem with your Coleman furnace., the following codes can help you find out what’s wrong. 

  • Slow green flashing means that the furnace is working perfectly.
  • Slow amber flashing means that the furnace is operating normally and calling for heat.  
  • Rapid amber flashing is a warning of a low flame sense current. Do you have a weak flame, or is your flame sensor defective? 
  • One red flash is a sign that there is a flame, but the gas is turned off. This is very dangerous. You must immediately check if the gas valve is leaky.
  • Two red flashes signal a problem with the pressure switch. You need to check the wiring. If the wiring is OK, the switch could be faulty. 
  • Four red flashes indicate a problem with the limit switch. You need to check for dirty filters, an incorrect blower speed setting, or a faulty blower motor.
  • Five red flashes show that the roll-out switch is stuck while open. You should check if the inducer system is operating normally. If it is, the primary heat exchanger likely has a problem.  
  • Six red flashes indicate that the pressure switch has caused a furnace lockout. You need to fix or replace the switch then reset the furnace
  • Seven red flashes show that the ignition has a problem. Troubleshoot the furnace for a defective flame sensor, faulty gas valve, or malfunctioned burner.
  • Eight red flashes mean that there is ignition lockout due to repeated power cycles.
  • Nine red flashes mean there is a polarity problem.
  • Ten red flashes show that there is a flow of gas without a call for heating. This is also dangerous. Turn off the furnace immediately before you begin diagnosis. 

Bryant Furnace Codes

Like other units, Bryant furnaces use flashing LED lights to give you information about potential underlying issues whenever the heater isn’t operating normally or not working altogether. The codes are similar to Arcoair codes. Nevertheless, the following are the typical codes and their meanings. 

  • Error codes 12 and 44: This indicates that the blower calibration has a problem that needs to be addressed.
  • Error code 13: This shows that the limit switch and will auto-reset after three hours. So, you need to wait. 
  • Error code 14: Error code 14 on Bryant furnaces points to an ignition issue.  
  • Error code 41: This indicates that the blower isn’t turning at the required speed (revolutions per minute).
  • Error code 43:  This informs you that the pressure switch has a problem.
  • Error code 45: The furnace will be flashing yellow, showing that polarity has reversed. To fix this problem, you need to do proper polarity.

   Other codes include;

  • Red LED1 ON: This indicates that the furnace is operating in emergency heat. 
  • Red LED2 ON: This means that the microprocessor has a problem.
  • Yellow LED3 ON: The furnace is operating under high heat.
  • Green LED4 ON: The furnace is functioning in low heat.
  • Red LED2 is flashing: Means line voltage polarity is reversed.

Payne Furnace Codes

Payne furnaces have a built-in diagnostic system that reminds you when things are not going to plan. The furnaces have flashing LED lights within their control boards where error codes are displayed. The most common codes include;

  • Code 11: This means that no fault has been experienced in the last five cycles. So, it’s good news. 
  • Code 12: This one indicates blower calibration lockout. The good thing about it is that it auto-resets after a while.
  • Code 13: This shows limit switch lockout. It can either be successive limit trips due to high heat or successive trips due to low heat.
  • Code 14 and 34: These two typically indicate ignition lockout. Both errors are usually auto-resolved after some time. However, it would be best if you examined the valve on your incoming gas line. The lever is parallel when the gas supply is ON. 
  • Code 31: Indicates that the pressure switch is open. It could be stuck open or not getting enough negative pressure. Whichever the case, you need to diagnose the issue quickly.
  • Code 33: Indicates an open flame roll-out switch. Flame roll-outs can be dangerous. So, make sure to fix the underlying problem right away. 
  • Code 43: Signals a pressure switch calibration fault. You should check for improper switch wiring, possibly sagging pipes, etc.
  • Code 45: Signals circuitry lockout. Although the problem typically auto-resolves after one hour, you still need to find out the cause of the circuit lockout. Is it an open limit switch? Is gas supply ON? 

Keeprite Furnace Error Codes     

Understanding the basic error codes on your Keeprite furnace can help you take better care of the unit for a longer life or reliable use. The following are the most common codes decoded. 

  • Two flashes: Two flashes mean that the pressure switch has a problem. Specifically, it means that the switch is closed when it should be open. What’s keeping it open? Is it an electrical issue? Is the switch dirty? Or is it defective?
  • Three flashes: Three flashes are often observed when the pressure switch is open when it should be closed. To fix it, check for restricted exhaust vent, defective inducer motor, defective pressure switch, or tiny vent size.
  • Four flashes: Four flashes are only seen on a Keeprite furnace if the limit switch has a problem. You should check for proper vent sizing, dirty air filters, and a defective blower.
  • Five blinks: If your Keeprite furnace blinks five times, the flame sensor is out of sequence because the gas valve is stuck open.
  • Six blinks: Are seen when the ignition system has a problem, or the flame is lost while operating. To fix it, check if the flame sensor is ungrounded. Also, check for carbon monoxide build-up, a shut gas valve, and rough ignition.
  • Seven flashes: Seven flashes are a sign of limit circuit lockout. The furnace is ordinarily auto-reset after 3 hours.
  • Eight flashes: Signal a gas heating lockout. This may be due to a closed gas valve.
  • Nine flashes: Are a sign that the switch didn’t close even with medium or high pressure. Could it be stuck open? 
  • Ten flashes: Indicate that line voltage polarity is reversed. Review your owner’s manual to correct polarity.

Ruud Furnace Error Codes

If you are a Ruud home furnace owner and have recently encountered a few issues running the furnace, the blinking lights on the appliance can help with troubleshooting. The following are common patterns the flashing lights can make and what each blinking pattern means. 

  • LED light steadily ON: This means that a normal flame has been detected. It’s a sign that the furnace is working well.
  • Single LED flash: A single LED flash signals that the furnace has failed to detect a flame within three attempts from the time of ignition. In short, it has entered soft lockout. 
  • Two LED flashes: Two LED flashes are a sign of a pressure switch problem. You need to check your blowers and vents for air pressure. If everything else is working well, the pressure switch may be broken. 
  • Three LED flashes: Indicate that the limit switch is open or there is roll-out control. It could also mean that the inducer motor is working when it shouldn’t. You may want to check for a defective blower, loose blower wheel, or a dirty air filter.
  • Four LED flashes: Are a sign that the pressure switch is stuck closed, i.e., it won’t close no matter what. It could signal a defective pressure switch or an electrical issue. 
  • Six LED flashes: Six LED flashes signal that the poles are reversed. You need to diagnose the furnace’s wiring system. 


The biggest takeaway from this guide is that furnaces from all the leading manufacturers have diagnostic error codes that can be valuable during troubleshooting. So, that flashing LED light is the first thing you want to look at whenever you run into any issues. 

Does it light in a particular color? Perhaps red or orange? Does it flash a few times, stop, then start flashing again? It could be telling you about an underlying problem. 

Your job is to note down the color of the light, determine whether it’s flashing or continuous, and, if it’s flashing, note how fast it flashes. Also, count the number of flashes between pauses. 

Then, armed with this information, pull out your owner’s manual to find out what the light pattern means.