Carrier furnaces have the built-in self-diagnostic capability. If a system problem occurs, a flashing LED shows a fault code. In this guide, we’ll review some common Carrier furnace codes and how to read the error codes.
Carrier furnace error codes show in a two-digit number, with the first digit being the number of flashes by the yellow light and the second digit determined by the green light LED. When your furnace begins to blink, it means there’s a problem. The codes help you troubleshoot and ideally fix the issue before causing bigger problems.
Carrier Furnace Blinking Yellow Light
Carrier furnace continuously blinking YELLOW LED3 light indicates furnace is stuck in high fire mode, and continuously blinking GREEN LED4 light indicates furnace is stuck in low fire mode.
Typically, the furnace will run at low fire for up to 15 minutes, then switch to the high fire mode. Under most conditions, low fire mode will satisfy the thermostat and shut off the furnace before the high fire ever comes on.
If your Carrier furnace is stuck in high-fire mode, the flashing yellow light will appear as an error code. A furnace can get stuck in high fire mode due to a defective gas valve solenoid. Unfortunately, this problem can’t be repaired and needs to be replaced. You need to call a licensed HVAC technician to help out with the Carrier furnace blinking yellow light.
Carrier Furnace Error Codes
Here is the full list of error codes usually found on Carrier furnaces.
This guide uses your expertise and observations to lead you to the trouble spot as efficiently as possible. This Carrier furnace codes is only intended as a guide and should not be used blindly. Your experience and expertise are of high value when troubleshooting this unit.
Carrier Furnace Code 11
Problems: No-fault in recent history display.
This carrier furnace code indicates 1 of the following:
- No faults have occurred in the last 5 previous cycles, and setup switch SW-1 is in on position.
- The fault history can be cleared by jumpering r, w/w1, and y/y2 thermostat leads simultaneously while setup switch SW-1 is in on position.
How to fix carrier furnace code 11: Remove the blower access panel and depress the door switch.
Carrier Furnace Code 12
Problems: Blower calibration lockout.
This fault indicates that blower motor speed calculated for low heat is either less than 250 rpm or greater than 1300 rpm on 2 successive attempts at calibration.
How to fix carrier furnace code 12: Turn the power off, wait 30 sec, and then restore power. Reset thermostat. Observe operation of the furnace through 1 heating cycle. If the problem occurs, you may need to replace the blower motor or blower control module attached to the blower motor.
Carrier Furnace Code 13
Problems: Limit switch lockout
This fault indicates the limit switch has tripped 10 times in a row in a high fire or 3 times in a row in a low fire during a call for heat.
After 2 low-fire limit trips, the control is locked into high-heat mode; however, a third low-heat cycle can be forced due to excessive restriction in the air delivery system. Boards with date codes of 9506 or later will lock into high-heat mode after 2 low-fire limit trips and cannot be forced into a third low-heat cycle. Therefore, units with these boards can only lockout if the limit switch trips 10 times in a row in a high fire during a call for heat.
How to fix carrier furnace code 13:
- Reset the flame roll-out switch.
- Replace limit switch.
- Sometimes it also affects the control board.
Carrier Furnace Code 14
Problems: Ignition lockout.
This fault indicates the system failed to ignite the gas and prove flame in 4 attempts. This fault could also indicate the gas valve relay on the furnace control board is stuck closed, or there is a miswire/short to gas valve wiring.
How to fix carrier furnace code 14 : There is a miss wire or short to gas valve wiring. Call professional for help.
Carrier Furnace Code 21
Problems: Invalid model selection.
Personality connector pl5 is either not connected or jumpered wrong.
How to fix carrier furnace code 21: Replace or rewire the personality connector.
Carrier Furnace Code 22
Problems: Setup error.
This fault indicates that setup switches sw-1 or sw-6 are ON when they should be OFF. The following combinations will cause the fault:
- Thermostat call with SW-1 ON.
- Thermostat call with SW-6 ON.
- Sw-1 and SW-6 are both ON together.
How to fix carrier furnace code 22: Disconnect all thermostat terminal lead. Switch SW-1 in OFF position. Switch SW-6 in OFF position.
Carrier Furnace Code 23
Problems: Invalid blower airflow selection.
This fault indicates an improper a/c or cf switch setting. The -14 units can deliver sufficient airflow for 1-1/2 to 3-1/2 tons a/c and 600 to 1400 cfm for a continuous fan. The -20 unit can deliver sufficient airflow for 2 to 5 tons a/c and 800 to 2000 cfm for a continuous fan. If the fault code is flashing, the unit still operates, but it defaults to the closest allowable airflow.
Carrier Furnace Code 24
Problems: Secondary voltage fuse is open.
It Indicates the fuse is open and there is a short in low-voltage wiring.
Carrier Furnace Code 31
Problems: High-pressure switch fault.
Keep in mind that whenever the furnace control board shuts the unit down, gas shuts off immediately, the inducer continues running for 15 sec, and if the blower is running, it remains running at low-heat speed or reduces to low-heat speed for selected off delay.
How to fix carrier furnace code 31:
- If the high-pressure switch makes during pre-purge or just after ignition, the furnace control board continues operating until burners are lit, and inducer rpm is within 10% of calculated low-fire rpm. If the high-pressure switch remains made, the furnace control board starts flashing fault code 31, shuts the unit down, waits 2 minutes, stops flashing fault code 31, and restarts the heating cycle.
- If a high-pressure switch makes during low heat, the furnace control board starts flashing fault code 31, shuts the unit down, waits 2 minutes, stops flashing fault code 31, and restarts the heating cycle.
- If the high-pressure switch opens during high heat, the furnace control board starts flashing fault code 31 and ramps inducer rpm up until the high-pressure switch remakes. When the high-pressure switch remakes, the furnace control board stops flashing fault code 31 and continues the heating cycle.
- If the high-pressure switch does not remake within 45 sec after opening, the furnace control board continues flashing fault code 31, shuts the unit down, waits 2 minutes, stops flashing fault code 31, and restarts the heating cycle.
Carrier Furnace Code 32
Problems: Low-pressure switch fault.
How to fix carrier furnace code 32:
- If low-pressure switch does not make within 45 sec after call for heat is initiated, furnace control board starts flashing Fault Code 32, shuts unit down, waits 2 minutes, stops flashing Fault Code 32, and restarts heating cycle.
- If low-pressure switch opens before ignition, furnace control board starts flashing Fault Code 32 and ramps inducer RPM up until low-pressure switch remakes. When low-pressure switch remakes, furnace control board stops flashing Fault Code 32 and continues heating cycle.
- If low-pressure switch opens during low heat, furnace control board starts flashing Fault Code 32, shuts unit down, waits 2 minutes, stops flashing Fault Code 32, and restarts heating cycle.
Carrier Error Code 33
Problems: Limit switch fault.
This fault indicates the limit switch, rollout switch or auxiliary limit switch is open or unit is operating in high-heat only mode due to 2 successive low-heat limit trips.
How to Fix carrier furnace code 33: Reset the furnace. Turn the power off, remove the blower access panel, and disconnect the R thermostat lead.
Carrier Error Code 34
Problems: Ignition proving fault.
This fault can indicate 1 of the following:
- The flame was not sensed during the trial for the ignition period. The control will repeat the ignition sequence 3 more times before going into fault 14.
- The flame signal was lost after the trial for the ignition period.
- The flame signal was sensed while the gas valve was de-energized. The inducer will run at full speed until the fault is cleared.
Carrier Error Code 41
Problems: Blower outside valid speed range.
This fault indicates 1 of the following:
- Blower motor speed cannot be maintained within 10% of calculated speed over a 30-sec period.
- Blower motor speed is less than 250 rpm or greater than 1300 rpm for more than 10 sec.
Carrier Error Code 42
Problems: Inducer outside valid speed range.
This fault indicates that the inducer motor is not operating at calculated rpm or has not started within 10 sec after a call for heat.
How to fix carrier furnace code 42: Check the wire to motor: Jumper R and W/W1 thermostat terminals on furnace control board.
Carrier Error Code 43
Problems: Pressure switch calibration fault.
Indicates low-pressure switch and high-pressure switch make points during high-heat purge are not within the calibration range.
Carrier Error Code 44
Problems: Blower calibration fault.
This fault indicates that the calculated blower motor speed is below 250 or above 1300 rpm.
How to fix carrier furnace code 44: Check for undersized ductwork or excessive static caused by a dirty filter or closed registers.
Carrier furnace error codes can provide important information when troubleshooting a furnace. A furnace troubleshooting can often result in an easy fix, but sometimes you have to contact a professional HVAC technician. They will evaluate the whole system and provide you with better solutions.