Blinking Red Light On Furnace Meaning [Lennox, Trane, Goodman And More]

Today's furnaces frequently come with an LED light installed on the circuit board to help you figure out what's going on with the system. You might wonder what a blinking red light means on a different model of furnace. We’re here to help and have gathered information from experts to determine what a blinking red light means.

For Lennox, Trane, Goodman, York, Bryant, Rheem, and Carrier furnaces, the red light on the heater communicates with you using the same principle of Morse Code. The number of times the light flashes corresponds to a specific code that denotes a specific issue. It is also communicating that basic HVAC maintenance is needed.

This article will explain how you read the red light codes for each furnace, how to interpret the codes and figure out what's wrong with your furnace. So keep reading!

Home high efficiency Goodman furnace, Blinking Red Light On Furnace Meaning [Lennox, Trane, Goodman And More]

Meaning of Blinking Red Light On Furnace 

Each manufacturer has its own set of codes that describe the red blinking light on the furnace, which will be covered here.


Lennox sign logo

Lennox furnaces have two LED lights that flash red at different frequencies, and the meaning will be discussed below:

  • First LED blinks slowly, while the other stays on or steady. This shows that the high limit switch is open, which is a safety feature that prevents the HVAC system from overheating.
  • The first LED is slowly blinking, while the other is off. This means that your furnace failed to detect gas. A fault with the gas supply, valve, or ignitor control is possible. 
  • The first LED is off, while the second is slowly blinking. This means either the draft inducer is broken or the pressure switch circuit is closed.
  • Both LEDs alternate blinking slowly one after the other. This means the furnace's flame system has failed as a result of a malfunctioning HVAC system, which could be caused by a problem with the gas supply, valve, or ignitor control.
  • Both LEDs alternately blink quickly. This means the furnace isn't getting enough voltage to run properly. This could potentially indicate a problem with the ignitor in the furnace, which ignites the fuel.
  • The first LED flashes slowly, while the second blinks quickly. This shows that the flame level in the furnace is low, which can occur even if the furnace's heating system is working properly.
  • The first LED flashes quickly, while the second blinks slowly. This means your furnace's polarity is reversed, which could be caused by a problem with the heater's wiring.
  • Both LEDs are slowly blinking. This implies that the blower motor in your Lennox heater, which transports hot air from the HVAC system into your living space, isn't working properly.
  • One LED is flashing, while the other is steady. This implies that your Lennox furnace's flame rollout switch is open.


Trance logo

  • It is normal if the red light is flashing low. This means that it is not set for heat.
  • It is also normal if the light is flashing fast, especially when you raise the thermostat.
  • Two flashes indicate a lockout from the outside. After an hour, your furnace will restart.
  • Three flashes indicate a problem with the pressure switch.
  • Four flashes mean that the high limit switch tripped.
  • Five flashes indicate that there is a flame inside your unit that isn't supposed to be there.
  • Six flashes indicate either your grounding is bad or the polarity of the 115 volt AC (VAC) power is reversed.
  • Seven flashes is an error code generated by the gas valve circuit.
  • Eight flashes is an error message sent by the low flame sensor.
  • Nine flashes indicate an issue with the igniter.


Goodman high efficiency furnace

  • A single red flash that is steady indicates that the furnace is not receiving a signal from the thermostat and will not work.
  • A single flash that blinks on and off indicates that your furnace has locked out as a result of too many attempted ignitions.
  • Two red flashes indicate a malfunctioning draft blower or the pressure switch circuit in your furnace is shorted
  • Three red flashes indicate that your furnace's pressure switch circuit is open or that the induced draft blower is running when it shouldn't.
  • Four flashes signify that your furnace has a primary open limit circuit if this is the case.
  • Five red flashes indicate that your furnace detects a flame without receiving a call for heat.
  • Seven flashes indicate that the flame sense microamp signal is low. A coated flame sensor or a sluggish flame due to low gas pressure causes this.
  • Eight red flashes indicate that your furnace has an igniter circuit problem caused by a faulty or poorly connected igniter.
  • Nine flashes indicate that the furnace has a high-stage pressure switch that does not close during high-stage induced draft blower operation.
  • Continuous red flashes indicate that the furnace's 115-volt polarity is inverted.


York logo

  • A single red-colored flash on your York Furnace indicates that the gas valve isn't receiving electricity. There could be a gas leak at the valve.
  • Two red lights indicate that the pressure control switch is possibly stuck. This error code will appear if this switch becomes stuck in the 'closed' position.
  • If you witness three red-colored flashes, your pressure switch is most likely locked in the 'open' position.
  • The "high-limit" switch may be open if four red-colored flashes appear. This York Furnace error code could be caused by a clogged air filter or restricted airflow.
  • If you see five red-colored flashes on your York Furnace, it means the roll-out switch, also known as the auxiliary switch, is open. By pressing the middle of your furnace's red button, you can reset this switch ( it should be located on the side ).
  • The modulating gas valve in your furnace has failed if you see six red-colored flashes. This valve will require replacement.
  • The presence of seven red lights indicates that your furnace is in "lock-out mode." If three attempts to relight the device fail, "lock-out mode" will be activated for one hour. After the hour has passed, another attempt to relight will be made.


The Bryant furnace uses a sequence of LED lights or a 2-digit code with short and long light flashes. The first digit of the two-digit code is indicated by the short flashes, and the second digit is indicated by the long flashes.

  • If the first red LED is on, it means that the furnace is currently providing emergency heat. Unless you chose to start this option on purpose, having it start up automatically usually suggests you're having problems.
  • If the second red LED is on, it means the microprocessor is malfunctioning. Microprocessors are used to keep track of a room's temperature. You'll need to reset your furnace if you get this problem code.
  • If the second red LED is flashing, it indicates that the line voltage polarity is inverted. It may also mean that the circuit board is encountering trouble. In most circumstances, a circuit board will need to be changed once it begins to malfunction.
  • 13 (one short flash – three long flash) means that the limit switch is tripped. The furnace will automatically reset every 3 hours.
  • 14 means that the ignition is malfunctioning. After 3 hours, the control will automatically reset.
  • 23 indicates that the airflow selection on the blower is problematic.
  • 34 indicates that the ignition system isn't working properly.
  • 41 indicates that the blower isn't working properly because it is supposed to turn at a set rate.
  • 43 means that there are problems with the pressure switch calibration.
  • 44 and 12 indicate that the blower calibration isn't working properly.
  • 45 signifies that the control circuitry is having issues and is now locked out. After an hour, the system will reboot.


  • If the red light flashes rapidly, it means there’s an unexpected flame.
  • If the red light flashes slowly, it means marginal flame sense.
  • Steady light red means normal flame detected.
  • A single flash means there’s an ignition failure and after 1 hour it will lock out.
  • Two flashes mean that when the inducer is turned on, the pressure switch is stuck open and will not close. Examine the exhaust and intake flue venting, as well as the pressure switch.
  • Three flashes mean that the main limit or roll-out control is open. Replace the furnace filters as needed.
  • Four flashes mean that the pressure switch is stuck shut. The switch will not be activated.
  • Six flashes mean that the line and neutral wires are reversed. 


Carrier corporation sign and symbol

When working with a Carrier furnace, keep an eye on the number of times the LED light flashes and the speed with which it flashes. The short flashes decode the initial digit while the long flashes represent the second digit. 

  • If the red light is rapidly flashing, it means that the polarity is inverted.
  • 11 (one short flash – one long flash) means that previous codes are wiped off.
  • 12 means that when you turn on the unit, the blower starts.
  • 13 means that the switch that controls the roll-out has been disabled.
  • 14 means that the ignition has been disabled.
  • 21 means that the gas heating system is broken.
  • 22 signals an abnormal flame-proving.
  • 23 means that the pressure switch didn't work.
  • 24 means that there is an open secondary voltage fuse.
  • 31 means that the draft guard or aux-limit switch was not properly closed. The vent switch may also be obstructed.
  • 33 means that the flame roll-out or limit switch is open.
  • 34 means that there’s a problem with the ignition.


When you see a blinking red light on a furnace, your system is sending you an error code. The lists above can help you narrow down the possible causes of your furnace not working properly. If you can't decode the blinking red light, you should call an HVAC technician to help identify the problem. 

Check out these related blog posts for more information. 

Do Electric Furnaces Need Yearly Maintenance?

How To Clean An Electric Furnace?


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