A red blinking light in the furnace could mean any number of things. While some of the issues can be fixed with a do-it-yourself approach, others may require professional help.
Try out some of these potential solutions before you pick up the phone to call in the experts.
What does a blinking red light on the furnace mean?
Unfortunately, a blinking red light isn’t always a cut-and-dried problem. Each manufacturer has their own specific set of codes that indicate the issue.
Once you have this code, you’ll want to reference the code chart. This may or may not be listed in the owner’s manual. You’ll have to check, but it definitely should be displayed on the furnace compartment door. For your convenience, some of the most popular furnace brands and their red-light codes are listed below.
So, how does this all work? If the code repeats the same dot pattern continuously with tiny breaks between the sets, then it’s a single digit. For an example, a “dot, dot, dot, dot, pause, dot, dot, dot, dot” pattern would communicate a “4” code.
Double-digit numbers are displayed a little differently. These codes are displayed repeatedly as “dot, dot pause, dash, dash, dash, dash, pause.” That would be a “24” code. It really is that simple once you know how to read the codes.
Once the pause is over, this pattern will continue to repeat itself until the issue is corrected.
Trane furnace blinking red light
| Code | Result | Fix |
| Flashing slow | This is normal. The furnace is not set for heat. | You only need to worry if your furnace doesn’t respond after raising the thermostat. |
| Flashing fast | This is normal when you raise the thermostat. | The only time you should be worried is if your thermostat is non-responsive. |
| Always on | This is an issue with your furnace’s control panel. | You’ll need to completely replace the control panel. |
| Always off | Check your furnace’s power supply. | Make sure your furnace is getting adequate power. |
| 2 Flashes | This is an external lockout. Your furnace will reset after 1 hour. | Inspect your furnace for miswiring, humidity within the device, and a clogged pilot tube. |
| 3 Flashes | There’s an issue with the pressure switch. | Inspect the drain tubes. Look to see if there’s too much moisture within them or if they’re clogged with debris like dirt. |
| 4 Flashes | The high limit switch tripped. | There’s a problem with the thermal protection. Replace the air filters and see if the issue corrects itself. If not, then it may be caused by loose wires or a blockage in the flue. |
| 5 Flashes | A flame exists inside of your unit, but it really shouldn’t be there. | Inspect the faulty flame sensor and see if there’s a stuck gas valve or if the gas valve is leaky. |
| 6 Flashes | You either have a poor grounding issue, or the polarity of the 115 VAC power has been reversed. | You’ll need to get the voltage polarity correct. Also, check and replace the wiring if need be. |
| 7 Flashes | The gas valve circuit is giving off an error code. | Inspect your furnace’s gas valves for any damage. |
| 8 Flashes | The low flame sensor is sending an error message. | Make sure the flame sensor is not malfunctioning. Check if your furnace has a low gas pressure issue. |
| 9 Flashes | The igniter is giving off an error code. | The igniter may need to be replaced. |
Goodman furnace blinking red light
| Code | Result | Fix |
| Steady on | Normal Operation | – |
| Off | There is a control failure. | You’ll need to replace the control board. |
| 1 Flash | The system is locked out. You’ve exceeded the retries. | You just have to wait an hour. After that time, your furnace will reset. |
| 2 Flashes | Your furnace’s pressure switch is stuck shut, or the draft inducer is having problems. | The pressure switch will need to be fixed or replaced. |
| 3 Flashes | Your furnace’s pressure switch is stuck open. | Look for blockages in the pressure switch hose. Also, look for an improper connection. |
| 4 Flashes | Your furnace’s high limit switch is open. | All the filters in your furnace should be cleaned. If they’re old, they should be replaced. Also, check to see if the flue has any blockages. |
| 5 Flashes | The furnace senses a flame, but the thermostat is not calling for heat at the moment. | Inspect the gas valve and make sure it’s not open or leaking. Also, make sure there’s no lingering burner flame. |
| 6 Flashes | The issue here is an open roll-out switch or an open fuse. | To resolve this issue, replace the fuse. |
| 7 Flashes | Low flame signal | Read the owner’s manual and adjust your gas pressure accordingly. The flame sensor may also need to be cleaned. |
| 8 Flashes | Igniter circuit problem | Either the igniter is defective, or the igniter is not connected properly. Replace or reattach the igniter. |
| 9 Flashes | The high-stage pressure switch is stuck open while a high-stage-induced draft blower operation is taking place. | Check the switch hose and make sure it’s not pinched, or the pressure switch hose isn’t being blocked. You can also try replacing the furnace filter. |
| Continuous LED flashing | The polarity of 115 VAC has been reversed. | Review the wiring diagram in the owner’s manual and reconnect the wiring polarity. |
York furnace blinking red light
The codes emitted from a York furnace are pretty simple to read. The number of red flashes relates to a specific issue.
One flash
If you see one red flash, it means that something is not allowing power to get to the gas valve. This may be attributed to a leaky or slow closing gas valve.
Two flashes
When you see this error code, it means that the normally open contacts of your pressure switch are stuck in the closed position. You’ll either need to clean it if it’s dirty or replace it if it’s bad.
Three flashes
This typically means that your pressure switch is jammed and stuck in the open position. You’ll either need to clean the switch or replace it.
Four flashes
The high-limit switch is more than likely open. This is usually attributed to a clogged air filter. Restricted airflow can also be the issue here. You’ll need to inspect your unit and see if you can tell where the air is getting restricted at.
Five flashes
This error code means that either the auxiliary switch or the roll-out switch may be open. You’ll need to do a reset here. Do this by pushing the middle portion of the red button located on your furnace. The button is located on the side of the unit.
Six flashes
This error code is attributed to a failed modulating gas valve. It’s best to replace this valve as soon as you can.
Seven flashes
When you see this error code, it means that your furnace is experiencing a lockdown. This happens after the furnace has tried three times to reignite itself but was unsuccessful in doing so. This lockdown will last for 1-hour. The furnace will try to reignite itself again.
Luxaire furnace blinking red light
| Code | Result | Fix |
| Rapid red flash | This is a twinning error. The 24V phasing is incorrect. | The best way to fix this issue is to check the twinning wire. You should also check the transformer. |
| 1 Red flash | This error code is displayed when the system senses a flame when the heat isn’t turned up. | Clean the gas valve. It’s clogged with dirt, or the valve may need to be replaced if it closes slowly. |
| 2 Red flashes | The pressure switch is faulty. It’s more than likely stuck in the closed position. | There’s a miswiring issue, or the pressure switch will need to be replaced. |
| 3 Red flashes | This code means that the open pressure switch did not shut after the inducer became energized. | Some of the issues that can cause this problem include a blocked vent pipe, a faulty pressure switch hose, a broken pressure switch, or a faulty inducer. |
| 4 Red flashes | This means that the normally closed contacts of an auxiliary or primary limit switch have been opened. | A dirty filter, incorrect blowing blower speed setting, incorrect firing rate, wrong-sized ductwork, or a broken blower motor are the issues that can cause this error code. |
| 5 Red flashes | If the normally closed contacts in the roll-out switch open up, you’ll receive this code. It’s important to note that the roll-out control is manually set. | When receiving this code, make sure the combustion air is where it should be, the inducer is working properly, if there is a burner problem, or if there is a primary heat exchanger failure. |
| 6 Red flashes | This code means that the pressure switch became open four different times when the temperature on the thermostat was raised. | Check to see if the main blower in your furnace is in a “Delay On” mode. If it is, the mode will automatically complete it. Your furnace will be locked down for one hour, and then it’ll restart. |
| 7 Red flashes | You’ll receive this code when the flame cannot be established. Your furnace will lock out for an hour. | The problem is usually due to low gas pressure, a faulty gas valve, a faulty hot surface ignitor, or even a burner problem. |
| 8 Red flashes | If the flame is lost five times during one heating cycle, you’ll receive this code. | Low gas pressure or a broken gas valve may be the problem here. Typically, when you exceed the five times, your furnace will lock out for an hour and then restart. |
| 9 Red flashes | This error message is displayed when there’s a grounding issue, or the voltage polarity has been reversed. | First, inspect the furnace and the branch for the right polarity. You’ll also want to make sure the furnace grounding is correct and that the flame probe has not been shorted. |
| 10 Red flashes | This error code is displayed when the gas valve became energized by itself, meaning no one turned up the thermostat. | More than likely, the problem is with the gas valve or the gas valve wiring. |
| 11 Red flashes | This error message means that the normally closed contacts for the limit switch have been open for more than 5 minutes. | A failed blower motor or blower wheel is typically the cause of this error message. |
Lennox furnace blinking red light
The normal operation of a Lennox furnace is as follows:
- When both lights flash slowly, the furnace is heating the way it’s designed to.
- When both lights are flashing fast, the heating system is requesting more heat. Like when you turn the thermostat up in temperature.
When your furnace has a low flame, you may see one light blinking fast and one blinking even faster. The flame sensing rod just might need to be cleaned or positioned incorrectly on the burner.
What do you do when your heating system refuses to turn on? First, you have to diagnose the problem. Listed below are some light patterns you may see displayed on your Lennox furnace.
Both of the LED lights are off
The main reason this may be happening is because your furnace isn’t getting power. You’ll want to check your breaker box to ensure that the furnace switch didn’t get accidentally flipped off. If the fuse did, in fact, get flipped, make sure you reset the fuse.
One light is blinking, and the other is steadily on
If you’re receiving this error code, more than likely, the problem is a faulty flame roll-out switch. This is an important part of the furnace. It helps prevent fires and the exposure to carbon monoxide. If you have no experience dealing with problems like this, then it’s best to call a professional.
One light is blinking fast, and the other is blinking slowly
When you see this being displayed, the problem is typically that your furnace’s polarity power has been inverted. A wiring problem is generally the cause of this issue.
Both of the lights are blinking slowly
In this situation, the most likely reason for this problem is the blower motor. The blower motor’s function is to move warm air through the vents of your furnace into your house.
One light is blinking rapidly, and the other is blinking slowly
A short circuit or a low voltage problem is the cause of this error code.
One light is blinking on-on-off while the other light is blinking on-off-on
This code is letting you know there might be an issue with the motherboard or the wiring.
Alternate slow blinking LEDs
A flame error is typically the cause of this issue. Check your gas supply and make sure it’s not low. A faulty gas valve or ignitor control may need to be replaced. Also, you should check the gas supply.
One light stays on steadily while the other flashes slowly
This error code is letting you know that the heating system’s limit switch is stuck open and needs to be shut. This switch prevents your HVAC system from overheating.
The lights are blinking rapidly but also simultaneously
When you see the lights on your furnace do this, it means that your blower motor is running, but no heat is being produced. The problem is more than likely the ignitor and will need to be replaced.
Coleman furnace blinking red light
| Code | Result | Fix |
| Steady on red | The problem is a control failure. | Check the control unit and replace it if it is necessary. |
| Rapid red flashing | The issue is a twinning problem. The 24V phasing is probably incorrect. | Check the twinning wiring. |
| Rapid amber flashing | The issue is a low flame sense current. | The flame sensor needs to be cleaned. The problem could also be improper gas flow. |
| 1 Red flash | There is a flame present, but the gas is turned off. | Start by checking the gas valve. It may be leaking or closing slowly. |
| 2 Red flashes | The issue here is that the pressure switch is jammed in the closed position. | Miswiring or a faulty pressure switch is the problem. |
| 3 Red flashes | This code means that the pressure switch is jammed in the open position. | A bad inducer, a blocked vent pipe, a bad pressure switch, or a damaged pressure switch hose are likely the issues. |
| 4 Red flashes | This code relates that your furnace’s limit switch is stuck while being open. | The problem is typically a dirty air filter, the wrong-sized ductwork, the wrong blower speed setting, or a bad blower motor. |
| 5 Red flashes | The roll-out switch is jammed while being open. | The roll-out control will automatically be reset. The problem is more than likely the inducer. The primary heat exchanger could also be faulty here. |
| 6 Red flashes | The pressure switch cycle is locked out. | You have nothing to worry about. For an hour, the furnace will lock out. Then it will reset itself. |
| 7 Red Flashes | There have been too many tries, and now there is an ignition lockout. | The problem is likely a bad gas valve. The flame sensor could also be dirty or bad. Other problems can include a bad hot surface ignitor or a bad burner. |
| 8 Red flashes | Because of repeated power recycles, the ignition has been locked out. | A filthy or damaged flame sensor may be the problem here. Low gas pressure can also be responsible for this error code. |
| 9 Red flashes | The problem is either a line polarity or a grounding issue. | Inspect the polarity of the furnace and the branch. |
| 10 Red flashes | Even though there’s no request for heat, the gas continues to flow. | The issue is either a bad gas valve or the gas valve wiring. |
American Standard furnace blinking red light
| Code | Result |
| 2 Flashes | Your furnace is probably blowing cool air because there is no flame. |
| 3 Flashes | There is an issue with the pressure switch. |
| 4 Flashes | There is an issue with the limit switch. |
| 6 Flashes | There is a problem with the grounding or the polarity. |
| 7 Flashes | The gas valve is faulty and needs to be replaced. |
| 9 Flashes | The ignition or the ignition circuit is bad. |
| 22 Flashes | There is an issue with the flame. |
Carrier furnace blinking red light
When working with a Carrier furnace, always remember to pay attention to how many times the LED light flashes and the speed at which it flashes.
To read these codes, remember that the first digit is decoded by the number of short flashes. The second digit is decoded by the number of long flashes. Listed below is a code chart for the Carrier furnace.
| Code | Result | Fix |
| Continuously on | 24VAC power | – |
| Rapid flashing | The polarization has been reversed. | Check the twinning wiring. |
| One short flash – One long flash | Stored previous codes are erased. | This happens when the power of the device is interrupted. |
| One short flash – Two long flashes | The blower is on after you power the unit up. | If the furnace is powered up after the thermostat is turned up, the blower will run for 90 seconds. |
| One short flash – Three long flashes | The roll-out switch has been locked out. | After 3 hours, the control will automatically reset. All you have to do is reset the switch or replace the fuse link if need be. |
| One short flash – Four long flashes | The ignition has been locked out. | After three hours, the control will automatically reset. |
| Two short flashes – One long flash | Gas heating is experiencing a lockout. | The control will not automatically reset. Inspect the gas valve to see if it’s bad or wrongly wired. |
| Two short flashes – Two long flashes | Abnormal flame-proving signal | The gas valve has been de-energized. Look for a leaky gas valve or see if the gas valve is stuck open. |
| Two short flashes – Three long flashes | The pressure switch failed to open. | See if the pressure switch is obstructed in any way. The pressure switch could also be stuck. |
| Two short flashes – Four long flashes | The secondary voltage fuse is open. | Inspect the wiring in the secondary voltage (24VAC) for a short circuit. |
| Three short flashes – One long flash | The draft safeguard or the aux-limit switch did not close properly. The vent switch could be blocked as well. | Unblock or replace the vent switch. You also may have to replace the aux-limit switch or the draft safeguard. |
| Three short flashes – Three long flashes | The problem here is the flame roll-out or limit switch is open. | Close or replace the limit switch or the flame roll-out switch. |
| Three short flashes – Four long flashes | Ignition-related failure | The ignition system may need to be replaced. |
Bryant furnace blinking red light
The codes that are used by the Bryant furnace are a series of LED lights or a 2-digit code with short and long flashes of light.
Red LED1 on: The furnace is performing in emergency heat.
Unless you purposely chose to start up this setting, having this automatically happen typically means you have trouble. The best thing to do in this situation is to call a furnace repair technician.
Red LED2 on: The microprocessor is not working correctly
Microprocessors are designed to monitor the temperature of a certain room. When you receive this error code, you’ll need to reset your furnace.
Red LED2: Flashing
The line voltage polarity is reversed when you see this error code. The red LED2 light might also be flashing if the circuit board is having problems. In most cases, when a circuit board starts giving your problems, it’ll need to be replaced.
Bryant Error Code Chart
| Code | Clarification |
| Error codes 12 and 44 | The blower calibration is having issues. |
| Error code 13 | There is an issue with the limit switch being tripped. Every three hours, the furnace will automatically reset itself. |
| Error code 14 | There’s a problem with the ignition. The control will automatically perform a reset after 3 hours. |
| Error code 23 | The blower airflow selection is having issues. |
| Error code 34 | The ignition is not performing as it was designed to. |
| Error code 41 | The blower is designed to operate at specific revolutions per minute, and if you get this code, it’s not operating correctly. |
| Error code 43 | The pressure switch calibration is experiencing issues. |
| Error code 45 | The control circuitry is experiencing problems and is experiencing a lockout. The system will reset itself after an hour. |
Ducane furnace blinking red light
| Code | Clarification |
| 1 Flash | The gas valve is off, yet the flame is present. |
| 2 Flashes | The pressure switch is turned off, and the inducer is off. |
| 3 Flashes | The roll-out or aux limit or low-fire pressure switch is currently open. |
| 4 Flashes | The high limit switch is open. |
| 5 Flashes | This setting is not used. |
| 6 Flashes | The pressure switch cycle has been locked out. |
| 7 Flashes | There’s a lockout because there’s no ignition. |
| 8 Flashes | Because of so many flame dropouts, the system has been locked out. |
| 9 Flashes | The polarity and the phasing are incorrect. |
Amana furnace blinking red light
| Code | Result | Fix |
| LED light stays on continuously | The furnace is getting no signal from the thermostat. | Check the connections and restart the unit. |
| 1 Flash | After three attempts to start up, the heating system has become locked. | You’ll need to find the interruption in the flow of gas and repair it. Do this by lowering the temperature a few seconds and raising it back to its original position. |
| 2 Flashes | The draft inducer is having problems. This error code could also be due to a faulty pressure switch. | You’ll either need to replace the pressure switch or fix the short in the pressure switch circuit. |
| 3 Flashes | The problem is that the pressure switch is open. | You’ll need to replace the pressure switch. |
| 4 Flashes | The primary limit switch is open. | The air filters need to either be cleaned or replaced. Also, clean the drain tubes. |
| 5 Flashes | A low closing valve is typically the cause of this error. This causes the system to sense a flame when you actually haven’t turned up the thermostat. | Turn off the gas. You’ll need to fix or replace the valve to solve this issue. |
| 7 Flashes | The flame sensor is bad. | Either clean the flame sensor if it’s dirty or replace the sensor if it’s bad. |
| 8 Flashes | You have a bad ignitor. | The ignitor will need to be replaced. |
| Continuous LED flashing | The polarity has been reversed. | In the owner’s manual, you should find a wiring diagram. Review it and fix the wiring, so you can get the polarity right. |
The most common issues causing a red light to flash
1. You’re getting no signal from the thermostat
If your thermostat is not sending a signal to your furnace, this lack of communication will cause the LED light to blink continuously. Some of the issues that could be causing this problem may be bad wiring within your walls or even a loose wire.
To resolve this issue, test all of your connections. If your wiring looks like it’s in good shape, then the problem is more than likely the thermostat.
2. You’re receiving a reverse polarity error code
The first thing you’ll want to do is check to make sure the polarity in your furnace is correct. If you have no experience doing this sort of thing, then you’ll want to call a real professional. This will ensure you don’t get injured and that the job gets completed right.
This is a typical issue with new furnaces. If you have an outlet that has reverse polarity, the electricity is continuously flowing out of the outlet. Even though your furnace can technically run on reverse polarity, down the road you will have problems. To fix this issue, the wiring in your outlet will need to be rewired.
3. Flame problem
If the flame is failing to ignite, the problem is a lack of a steady flow of gas or air. There are several possible causes of this. These causes include:
- Dirty burner chamber
- Clogged filters
- A dirty tank
- Damaged burners
- Too much pressure on the inside of the combustion chambers
To resolve this issue, start by cleaning the filters and replacing them if need be. Look in the burner chamber or the inside of the tank and clean out all the debris. Also, inspect the burner or the tank for anything that might be broken. When in doubt, call a professional to have a look.
4. Pressure switch failure
When the pressure switch goes bad, the bad gasses can’t be fully emitted. This can cause health problems and other potential issues.
To resolve this issue, you will need to replace the pressure switch. It’s also important to note that problems like a clogged condensate drain or another vent blockage can also be attributed to a bad pressure switch.
5. Gas valve problem
If there is not enough pressure to feed the gas through the gas line and into the combustion chambers, you will either need to adjust the pressure knob or replace the gas valve. A damaged gas valve can leak gas and lower the pressure.
6. Roll-out switch and the high limit switch
Roll-out switches are generally located on the inside of your heating system. Their purpose is to monitor for heat in areas where there’s not supposed to be any heat. The high limit switch detects when the heat exchanger is too high in temperature.
Typically, when you have a high limit switch error code, you will need to replace the filter.
7. Failure with the circuit board
If you’re getting a circuit board failure code, then your best bet is to call a professional. You’ll want to get the circuit board fixed or replaced as soon as you can before more problems arise.
8. Blower on after power up
If you’re seeing this code, don’t fret. Everything is working properly. You’ll also see this code anytime the furnace is being restarted or you’re starting your furnace for the first time. This code should stop flashing a few minutes after the system starts up.
Common troubleshooting ideas
If you have trouble getting your hands on a copy of the manual, there are some basic tactics you can try to resolve major issues with your furnace. These are things that you can tackle yourself before calling in the pros.
- First and foremost, try changing your air filters. Many homeowners don’t change these frequently enough. Experts recommend switching out your filters every thirty to ninety days, depending on your living situation. A clogged air filter can make your furnace work overtime to keep your home warm.
- Second, you can check to make sure that nothing is obstructing the airflow to your unit. You may want to check on the outside of your house to make sure that ice and debris aren’t clogging the intake or exhaust pipes. The flue may also have some blockages that need to be addressed in order to turn off the blinking light on your gas furnace.
- Third, check the thermostat to ensure that it is working properly. The furnace may not be coming on because the thermostat isn’t communicating with it clearly. Sometimes, this is what the blinking red light on the furnace indicates.Start by turning the thermostat up as high as it can go to see if it forces the furnace to produce hot air. If it does and the blinking red light stops, then you can rest easy and enjoy the warmth.
- Lastly, you can try resetting the furnace. This is the simplest task that you can do to try to get your furnace back in working order. Turn it off and let the unit rest for thirty seconds to one minute. Once you turn it back on, you may find that the unit magically works again for a while. If you do restart your furnace, leave it off for at least 30 seconds before turning it back on. By doing this, you’re clearing the board. Once it starts up, your unit will flash error codes if there’s a problem with the system. This is the best way to know what’s going on with your furnace.
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