Carrier Furnace Error Codes: Complete Diagnostic List
12 diagnostic codes documented · Official site ↗
🟡 Warning — Schedule Service
Blower On After Power Up
The Carrier error code 12, signaled by a specific LED blink pattern on the control board, indicates that the blower motor is running when it shouldn't be immediately after the unit powers up. This typically points to a problem within the system's control logic, preventing the blower motor from cycling on and off as expected. It's not a gas leak or immediate safety hazard, but it will likely prevent your system from heating or cooling your home effectively. This issue often arises from a faulty relay on the control board that's stuck in the 'on' position, or a miscommunication between the thermostat and the unit's control board. In some cases, it could also be a sign of a failing blower motor that's not responding correctly to the control signals. Because it involves electrical components, troubleshooting should be left to a qualified HVAC technician.
Pressure Switch Fault
The Carrier 23 error code, indicated by a specific blinking pattern on the unit's LED, signifies a problem with the pressure switch circuit. This switch is a crucial safety component that verifies proper venting before allowing the furnace to ignite. When the furnace induces draft, the pressure switch should close, proving that exhaust gases will vent properly. If the control board does not see the switch close, it will display error code 23 and shut down the unit to prevent potential hazards.
Secondary Voltage Fuse
The Carrier error code 24, or a blinking LED pattern of 2 long flashes followed by 4 short flashes, indicates a problem with the secondary voltage fuse. This fuse protects the low-voltage components of your Carrier system, such as the control board, sensors, and sometimes the thermostat. When this fuse blows, it means there's an overcurrent situation in the low-voltage circuit, which could be caused by a short circuit, a faulty component, or a wiring issue. The system will typically shut down to prevent further damage. Because this code relates to electrical components, it's important to have a qualified HVAC technician diagnose and repair the problem. They will be able to safely troubleshoot the electrical circuits, identify the cause of the blown fuse, and replace any faulty components. Attempting to fix this yourself without proper training and equipment could be dangerous and could potentially damage your system further.
High Stage Pressure Fault
The Carrier error code 31, or a blinking LED pattern indicating code 31, signals that the system's high-pressure switch has tripped during high-stage operation. This switch is a safety device designed to shut down the compressor when the refrigerant pressure gets too high, preventing damage to the compressor and other components. The high-stage refers to when the unit is operating at its maximum cooling or heating capacity. This error usually means there's a restriction in the refrigerant flow, a problem with the compressor, or an issue with the outdoor fan motor. It's important to address this issue promptly to prevent further damage to your HVAC system. Because this code indicates a locked-out system, you will likely need a professional to diagnose and fix the root cause.
Low Flame Sense
The Carrier error code 32, or a blinking LED pattern indicating 'Low Flame Sense,' means the furnace's control board isn't detecting a stable flame after ignition. The furnace goes through its normal start-up sequence, the gas valve opens, and the burners light. However, the flame sensor, a small metallic rod in the flame, isn't sending a strong enough signal back to the control board to confirm the flame is present. Because the furnace cannot reliably verify the flame, it shuts down as a safety precaution. This issue can stem from a few different problems, ranging from a dirty flame sensor to a more serious gas supply issue. Because gas furnaces are involved, it's important to address this issue promptly to ensure safe and reliable heating.
Ignition/Flame Sense Fault
Error code 34 on a Carrier furnace indicates an ignition or flame sensing issue. The control board isn't detecting a stable flame after the ignition sequence. This can happen for a few reasons, but it usually means the furnace has shut down as a safety precaution. The furnace will likely attempt to restart a few times before locking out completely, displaying the error code.
🔴 Critical — Shut Down Immediately
Limit/Rollout Fault
The Carrier error code 13, often displayed as a blinking LED pattern, signifies a 'Limit/Rollout Fault'. This means that either a limit switch or a rollout switch within your furnace has been triggered. These switches are safety devices designed to shut down the furnace when it detects potentially dangerous conditions like overheating or a flame where it shouldn't be. A limit switch monitors the furnace's internal temperature, and if it gets too hot, the switch opens, cutting off the gas supply. A rollout switch detects flames outside the normal burner area, indicating a potentially hazardous situation. Because this code indicates a potential safety issue, it's important to address it promptly. Continuing to run the furnace with this error could lead to equipment damage or, more seriously, a fire or carbon monoxide poisoning. Do not attempt to bypass any safety switches.
Ignition Lockout
The Carrier error code 14, also known as an ignition lockout, means your furnace tried to ignite the burners multiple times but failed. After several unsuccessful attempts, the control board locks out the system as a safety precaution. This prevents the continuous flow of gas into the combustion chamber, which could create a dangerous situation. This lockout requires manual reset in some cases, but should only be done after the underlying problem is resolved. Several factors can cause this issue, ranging from a faulty gas valve to a blocked flue. Because this code indicates a potential safety hazard related to gas flow and combustion, it's important to have a qualified HVAC technician diagnose and repair the problem. Do not attempt to troubleshoot gas-related components yourself.
Gas Heating Lockout
The Carrier 21 error code, also known as a gas heating lockout, signals that your furnace has tried to ignite the gas multiple times but failed. After several unsuccessful attempts, the system locks itself down as a safety precaution. This is often due to a problem in the ignition sequence or a detected hazard. It's important to address this issue promptly to restore heating and ensure your safety. Continuing to run a system with a lockout can potentially lead to dangerous conditions or further damage to the unit. Contact a qualified HVAC technician to diagnose and repair the problem.
Abnormal Flame
The Carrier 22 error code, often displayed as a blinking LED pattern on your furnace or HVAC system, signals that the system has detected an abnormal flame during operation. This could mean the flame is unstable, weak, or present when it shouldn't be. This is a serious issue because it could indicate a problem with gas combustion, potentially leading to a gas leak or carbon monoxide buildup. When this error occurs, the system typically shuts down as a safety precaution. Do not attempt to restart the system until the problem has been diagnosed and repaired by a qualified HVAC technician. Ignoring this error could lead to dangerous conditions in your home.
Limit/Rollout Switch Lockout
Error code 33 on your Carrier furnace signifies that the unit's control board has detected an open limit switch or rollout switch for longer than is considered safe. These switches are safety devices designed to shut down the furnace if it overheats or if flames are detected where they shouldn't be (like outside the burner box). The control board locks out after detecting this condition to prevent further operation until the issue is resolved. This lockout requires a manual reset, usually by cycling power to the furnace. This error is often triggered by a genuine safety concern, such as a blocked vent, a malfunctioning fan, or a cracked heat exchanger. It's crucial to address the underlying cause rather than simply resetting the furnace, as repeated lockouts could indicate a dangerous condition. Ignoring this error can lead to equipment damage, fire, or carbon monoxide poisoning.