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Better Know What The Blinking Red Light On Your Furnace Means

Better Know What The Blinking Red Light On Your Furnace Means

Today’s furnaces typically include an LED light mounted on the circuit board to assist you in determining what’s wrong with the system. You might be wondering what a blinking red light on a different model of furnace implies. We can assist you figure out what a blinking red light indicates.

The red light on the heater communicates with you using the same Morse Code principle as Lennox, Trane, Goodman, and York furnaces. The amount of flashes corresponds to a specific code that signifies a certain problem. It also communicates the necessity for simple HVAC maintenance.

You must be able to interpret the red light codes for each furnace in order to identify the problem with your furnace.

What Does A Furnace’s Blinking Red Light Mean?

We’ll go over the various codes each manufacturer employs to identify the furnace’s red blinking light.


Better Know What The Blinking Red Light On Your Furnace Means

Lennox furnaces have two red LED lights that flash at different frequencies, and the following will explain what they signify:

  • The first LED slowly blinks while the other LED is on or stable. This reveals that the HVAC system’s high limit switch, a safety feature designed to prevent overheating, is open.
  • While the first LED gradually flickers, the second is shut off. This means your furnace was unable to detect gas. There could be a problem with the gas supply, valve, or ignitor control.
  • The first LED is turned off, while the second blinks steadily. This indicates a problem with either the draft inducer or the pressure switch circuit.
  • Both LEDs alternately blink slowly one after the other. This implies that the flame system of the furnace has failed as a result of a broken HVAC system, which could be caused by a problem with the gas supply, valve, or ignitor control.
  • Both LEDs alternately blink rapidly. This implies that the furnace is not receiving enough power to operate correctly. This might point to a potential issue with the furnace’s ignitor, which ignites the fuel.
  • While the second LED blinks swiftly, the first LED flashes gradually. This indicates a low flame level in the furnace, which can happen even when the heating system is operating as it should.
  • While the second LED blinks slowly, the first LED flashes quickly. This indicates that the polarity of your furnace is inverted, which may be the result of a wiring issue with the heater.
  • Each LED is gradually blinking. This suggests that your Lennox heater’s blower motor, which moves hot air from the HVAC system into your living area, isn’t operating properly.
  • While the other LED is stable, the first one is flashing. This suggests that the flame rollout switch on your Lennox furnace is open.


Better To Know What The Blinking Red Light On Your Furnace Means
  • If the red light is flashing slowly, that is normal. It is not configured for heat, as indicated by this.
  • The light flashing rapidly is also common, especially when the thermostat is turned up.
  • A lockout is indicated by two flashes from the outside. Your furnace will restart an hour later.
  • The pressure switch is malfunctioning if there are three flashes.
  • When there are four flashes, the high limit switch has triggered.
  • If your unit flashes five times, there may be an unauthorized flame inside.
  • Six flashes signal a problem with your grounding or that the polarity of your 115 volt AC (VAC) power is inverted.
  • The gas valve circuit generates an error code of seven flashes.
  • The low flame sensor sends an error warning of eight flashes.
  • The presence of nine flashes indicates a problem with the igniter.


  • A single constant red flash indicates that the furnace is not getting a signal from the thermostat and will not operate.
  • A single flash that blinks on and off signals that your furnace has locked out due to too many failed ignition attempts.
  • Two red flashes indicate a faulty draft blower or a shorted pressure switch circuit in your furnace.
  • Three red flashes indicate that the pressure switch circuit in your furnace is open or that the induced draft blower is working when it should not be.
  • If you see four flashes, it means your furnace has a primary open limit circuit.
  • Five red flashes indicate that your furnace senses a flame but does not get a heat request.
  • The flame sense microamp signal is low after seven flashes. This is caused by a coated flame sensor or a slow flame caused by low gas pressure.
  • The presence of eight red flashes indicates that your furnace has an igniter circuit problem, which is caused by a malfunctioning or improperly connected igniter.
  • A high-stage pressure switch on the furnace that does not close when the high-stage induced draft blower is operating is indicated by nine flashes.
  • The polarity of the 115-volt power to the furnace is inverted, as shown by persistent red flashes.


Better To Know What The Blinking Red Light On Your Furnace Means
  • Your York Furnace’s solitary red flash is a sign that the gas valve isn’t getting electricity. The valve might be experiencing a gas leak.
  • A pressure control switch that has two red lights could be jammed. If this switch becomes stuck in the “closed” position, this error code will show up.
  • Your pressure switch is probably locked in the “open” position if you see three flashes of the color red.
  • Four red-colored flashes could indicate that the “high-limit” switch is activated.
  • If your York Furnace displays five red flashes, this indicates that the roll-out switch, also known as the auxiliary switch, is open. You can reset this switch by tapping the centre of your furnace’s red button ( it should be located on the side ).
  • If you witness six red flashes, the modulating gas valve in your furnace has failed. This valve will need to be replaced.
  • The presence of seven red lights means that your furnace is in “lock-out mode,” which will be activated for one hour if three attempts to relight the unit fail. After an hour, another attempt to relight will be undertaken.


When you observe a furnace with a blinking red light, your system is sending you an error code. The above lists can assist you in narrowing down the possible causes of your furnace not working properly. If you can’t figure out what the blinking red light means, contact an HVAC specialist for assistance.

Better Know What The Blinking Red Light On Your Furnace Means

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Written by HVAC Contributor

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