Before matching a Carrier furnace code
Match the furnace model before interpreting its flashes. A two-digit status pattern in the covered furnace manuals is different from a Greenspeed message on an Infinity control, and the 59SU5A has its own table below. Record the whole sequence through the observation window before a reset. A $99 diagnostic visit addresses the cause, not just the displayed number.
Keep the furnace door in place. Note whether the blower ran, whether heating began and when it stopped. If a limit or rollout fault is indicated, do not bypass the device or reset a rollout switch yourself. A dirty filter may be one item to check through normal owner access; it does not exclude a combustion or other safety problem.
A Carrier furnace tells you what’s wrong with an amber light on the control board. You see it through the small window in the blower door. A Carrier Greenspeed heat pump or AC does it differently: the outdoor unit sends a code like 18-11 to the Infinity thermostat on the wall. Both lists below come from Carrier’s own service manuals, and each one names the models it covers.
How to read the furnace light
The 59SC5B Comfort 95 manual puts it in one sentence. The amber LED is either on continuously, rapid flashing, or a code made of 2 digits. The first digit is the number of short flashes, the second digit is the number of long flashes. So code 33 is three short flashes, then three long ones.
The service label on the furnace door explains the three states that aren’t numbers:
- Continuous off: the control isn’t getting power. Carrier tells the technician to check for 115 volts at L1 and L2 and 24 volts at SEC-1 and SEC-2. For you, that means the breaker, the furnace switch and the blower door.
- Continuous on: the control has 24 volt power. Normal.
- Rapid flashing: line voltage (115 volt) polarity is reversed. The furnace won’t heat until that’s fixed.
Look before you open the blower door. The door has a safety switch, and Carrier’s 59TP6C manual warns that it removes 115 volt power to the control when the door comes off.
The control also remembers the last fault. Stored codes stay in memory when power is cut, and code 11 means there’s nothing stored, since stored codes are erased after 72 hours. Pulling the stored code means taking off the control door and briefly disconnecting a limit wire, so that’s a technician’s step.
Carrier furnace status code chart
This table is from the troubleshooting guide in Carrier’s 58SB0A Comfort 80 manual (Fig. 51, page 37) and the 59SC5B Comfort 95 manual (Fig. 69 and 70, pages 63 to 65). The two lists use the same codes. The 59SC5B adds code 32 and uses code 31 for its high pressure switch, as noted in the table.
| Code | What Carrier’s label says | What you can do |
|---|---|---|
| 11 | No previous code. Stored codes are erased after 72 hours. | Nothing. Run a heating or cooling cycle and watch. |
| 12 | Blower on after power up (115V or 24V). Normal operation. The blower runs for 90 seconds if the unit is powered up during a call for heat. | Nothing. |
| 13 | Limit circuit lockout. A limit or flame rollout switch was open longer than 3 minutes. Control will auto-reset after 3 hours. | Check the filter and registers (see 33). If it repeats, call. |
| 14 | Ignition lockout. System failed to ignite gas and prove flame in 4 attempts. Control will auto-reset after 3 hours. | Call a technician. |
| 21 | Gas heating lockout. Check for a stuck closed gas valve relay on the control, or a miswire or short to the gas valve wire. | Call a technician. |
| 22 | Abnormal flame-proving signal. Flame is proved while the gas valve is de-energized. Check for a stuck open or leaky gas valve. | Call a technician now. |
| 23 | Pressure switch did not open. Check for an obstructed pressure tube or a pressure switch stuck closed. | Call a technician. |
| 24 | Secondary voltage fuse is open. Check for a short circuit in the 24V wiring, including thermostat leads. | Call a technician. |
| 31 | 58SB0A: pressure switch did not close or reopened. 59SC5B: HPS (high pressure switch) did not close or reopened. | Call a technician. |
| 32 | 59SC5B only: LPS (low pressure switch) did not close or reopened. If open longer than 5 minutes, the inducer shuts off for 15 minutes before retry. | Call a technician. |
| 33 | Limit circuit fault. A limit or flame rollout switch is open. If open longer than 3 minutes, the code changes to lockout 13. | Check the filter and registers first. If it repeats, call. |
| 34 | Ignition proving failure. Flame wasn’t sensed during the trial for ignition. The control tries 3 more times before lockout 14. | Call a technician. |
| 45 | Control circuitry lockout. Auto-reset after 1 hour, due to a flame circuit failure, a gas valve relay stuck open, or a software check error. Replace control if code repeats. | Call a technician. |
The ultra-low NOx 59SU5A is different
Carrier’s 59SU5A ultra-low NOx furnace uses a pressure transducer and a burner thermal switch, so a few codes change. From its service label (Fig. 61, page 51):
| Code | What Carrier’s label says |
|---|---|
| 21 | Gas heating lockout. Control will NOT auto-reset. Check for a mis-wired gas valve, a defective control (valve relay), or 24VAC at the gas valve when it shouldn’t be there. |
| 23 | Pressure above 0.15 in. w.c. at start-up. Check for an obstruction in the pressure tubing or transducer vent holes, a defective transducer, or transducer wiring. |
| 25 | Invalid model selection or setup error. The model plug is missing or incorrect. |
| 26 | Burner thermal switch (BTS) open. If it is open during a call for heat, a permanent lockout occurs. Cycle power to reset the lockout. |
| 31 | Pressure transducer input does not sense target pressure, or pressure is out of range. |
| 42 | Inducer motor fault. RPM pulses are not detected from the inducer motor within 20 seconds after a heat request, or the RPM signal was lost. |
All of these are technician codes. A 26 means the burner thermal switch opened, and Carrier’s checklist for it starts with a blocked burner inlet, a blocked burner mesh and poor inducer flow. Find out which before anyone resets it.
The newer 59TP6C Performance 96 has a three-digit display instead of a blinking-only light. Its manual shows the idle state as iDl and an active fault as a number with a decimal. For example, reversed polarity shows as 10.1 with a rapid flashing light. Use the label on that furnace’s door for the rest of its codes.
Greenspeed heat pump and AC fault codes (24VNA6, 25VNA4)
On a Greenspeed system the code is reported by the thermostat. Carrier’s table lists a first number for the area and a second number for the exact fault, in two columns: fault and malfunction. In the manual’s own descriptions the malfunction number is the lockout. For example, 38-13 is a compressor start failure and 38-53 is the lockout after repeated start failures.
From Table 6, Fault Code Table, in the 24VNA6 / 25VNA4 service manual (pages 25 and 26):
| Code | What Carrier’s table says |
|---|---|
| 14-94 | Line Voltage Low |
| 15-94 | Line Voltage High |
| 17-06 | PCM-Bluetooth Module Communication Failure |
| 18-11 | Indoor Coil Freeze Protection |
| 24-58 | 5V PCM External Power Out of Range |
| 25-22, 25-24, 25-61, 25-62, 25-63 | Model Plug Missing (22, 62), Model Plug Changed (24), Invalid Model Plug (61), VFD/Equipment Model Mismatch (63) |
| 26-26, 26-27, 26-31 | PCM MCU Old Version, PCM Reprogramming Failure, EEPROM Write Failure |
| 28-71, 28-72 | Fuse 1 Open (PEV / RVS), Fuse 2 Open (LLV) |
| 31-11, 31-58, 31-16, 31-19 | Compressor High Pressure Limit (11, 58), High Pressure Switch Trip (16), High Pressure Disable (19) |
| 32-15, 32-55, 32-59 | Compressor Low Pressure Limit (15, 55), Low Pressure Disable (59) |
| 33-15, 33-55 | Compressor Low Discharge Limit |
| 34-11, 34-58 | Compressor High Temperature Limit |
| 35-11, 35-58 | Compressor High Compression Limit |
| 36-15, 36-55 | Compressor Low Compression Limit |
| 38-13, 38-53, 38-54, 38-18, 38-31, 38-71 | Compressor Starting Error (13, 53), Compressor No Pump (54), High Differential Pressure Start Disable (18), VFD Estimator Error (31, 71) |
| 39-13, 39-53, 39-14, 39-15, 39-55, 39-58 | Fan Start Error (13, 53), Fan Speed Error (14), Unexpected Fan Shutdown (15, 55), Fan Motor Error (58) |
| 41-13 | Defrost Overrun |
| 44-13 | PEV Timeout |
| 51-01, 51-02 | OAT (Outdoor Air Thermistor) Open/Low Temp, Shorted/High Temp |
| 52-01, 52-02 | OCT (Outdoor Coil Thermistor) Open/Low Temp, Shorted/High Temp |
| 53-41, 53-42 | OST (Outdoor Suction Thermistor) Open/Low Temp, Shorted/High Temp |
| 54-01, 54-02 | ODT (Outdoor Discharge Thermistor) Open/Low Temp, Shorted/High Temp |
| 57-01, 57-41, 57-02, 57-42, 57-43 | P1 Open (01, 41), P1 Shorted (02, 42), P1 Sensor Error (43) |
| 58-01, 58-41, 58-02, 58-42, 58-43 | P2 Open (01, 41), P2 Shorted (02, 42), P2 Sensor Error (43) |
| 61-41 | Reversing Valve Solenoid Open |
| 62-01 | PEV Solenoid Open |
| 64-41, 64-44, 64-45 | EXV-H Phase Open, Power Short to Ground, Phase Short to Ground |
| 65-41, 65-44, 65-45 | EXV-VI Phase Open, Power Short to Ground, Phase Short to Ground |
| 66-41, 66-42 | VFD Control Relay Coil Open, Shorted |
| 81-13, 81-53, 81-14, 81-54, 81-58 | PFC Error (13, 53), Unbalanced PFCM Error (14, 54), VFD System Wiring Error (58) |
| 82-11 to 82-57 | VFD Line Current Speed Reduction (11), VFD Reset with Power Dropout (13, 53), VFD Shutdown with Power Dropout (15, 55), Low Voltage Shutdown (16, 56), High Voltage Shutdown (17, 57) |
| 83-11 to 83-57 | Compressor Current Limit 1 and 2 Speed Reduction (11, 12), Current Limit 3 and 4 Shutdown (15, 55, 16, 56), Compressor Underspeed Shutdown (57) |
| 84-11, 84-58 | VFD Heat Sink Overtemp Shutdown |
| 85-13, 85-53, 85-14, 85-54 | DC Under Voltage Shutdown (13, 53), DC Over Voltage Shutdown (14, 54) |
| 86-06, 86-46 | VFD Communication Error |
| 87-13, 87-53 | VFD Initialization Error |
| 88-15 to 88-78 | Unexpected VFD Reset (15, 55), VFD Reprogramming Failure (27), VFD Internal Error: Current Sensor, IPM Temp Sensor, DC Link Sensor, PFCM Sensor A and B, Line Volt Sensor, PFCM Temp Sensor, DC Discharge (31 to 38, with lockouts 71, 73 to 76 and 78) |
Two of these often come from outside the outdoor unit. 14-94 and 15-94 are line voltage low and high. Carrier sets low below 180 volts and high above 285 volts, and the unit won’t run while either is active. The manual’s first checks are the incoming voltage and the tightness of every line voltage connection, then the utility. 18-11 means the outdoor unit is slowing the compressor to keep ice off the indoor coil, and Carrier names a dirty filter, restrictive ductwork and low refrigerant charge as the causes.
What you can check yourself
The filter. Codes 13 and 33 on the furnace and 18-11 on a Greenspeed all list a dirty filter or restricted ductwork. Replace the filter, open every supply register and clear the return grilles.
Power. No light on the furnace means no power to the control. Check the breaker, the furnace switch and that the blower door is fully seated.
The gas valve on a 34. Carrier’s first checks for an ignition proving failure are that the gas valve and the manual shut-off valve are turned on. If someone recently worked on the furnace and you know where its shut-off is, look. If you don’t, leave it for us. Don’t touch the flame sensor or the igniter.
One reset. Several codes reset on their own: 13 and 14 after 3 hours, 45 after 1 hour. Turning power off and back on starts the furnace over. If the same code comes back, the reset only hid it. Our Carrier ignition lockout guide goes through what usually causes a 14.
When it’s a technician’s job
Anything with gas, flame or venting is ours: 14, 21, 22, 23, 31, 32, 34 and 45 on the furnace, and the ultra-low NOx codes. A 22 means the control sees flame when the gas valve should be closed. Shut the furnace off and call. A rollout switch that tripped needs a manual reset, and Carrier’s list for it includes improper gas input and an inadequate combustion air supply. Someone has to find which one before it’s reset.
On a Greenspeed system, the pressure, compressor, fan, sensor, valve and inverter codes all come down to meters, gauges and the Carrier service app. A code tells us where to start testing, not which part to buy.
When to call us
Call (925) 999-4095 to schedule a visit.
Write down the code, the number of short and long flashes, and the model number from the furnace or outdoor unit label. Then call (925) 999-4095. Our diagnostic is $99, and we credit it toward the repair if you go ahead with us. You get a written estimate before any work starts. We service Carrier furnaces, heat pumps and AC systems across the Bay Area, usually same or next-day. See our Carrier service page.
Sources
The codes and descriptions on this page come from these Carrier manuals:
- Carrier 58SB0A / 58SB1A Comfort 80 installation, start-up, operating and service instructions: troubleshooting guide, Fig. 51, p. 37.
- Carrier 59SC5B Comfort 95 installation, start-up, operating and service instructions: status code LED and stored codes, p. 55 and 56; service label, Fig. 69, p. 63; troubleshooting guide, Fig. 70, p. 65.
- Carrier 59SU5A ultra-low NOx installation, start-up, operating and service instructions: service label, Fig. 61, p. 51.
- Carrier 59TP6C Performance 96 installation, start-up, operating and service instructions: system status display codes, Table 21, p. 54; start-up, p. 56.
- Carrier 24VNA6 / 25VNA4 Greenspeed service manual: diagnostic code descriptions from p. 15; fault code table, Table 6, p. 25 and 26.
Key takeaways
- A Carrier furnace status code is two digits. Count the short flashes for the first digit and the long flashes for the second. Code 33 is three short flashes, then three long ones.
- Steady on means the control has 24 volt power. Off means check power. Rapid flashing means the 115 volt polarity is reversed.
- Codes 13 and 33 are the limit codes. Carrier's checklist includes a dirty filter or a restricted duct system, so start with the filter.
- Greenspeed 24VNA6 AC and 25VNA4 heat pump codes show on the Infinity thermostat as two numbers, like 18-11. In Carrier's table the malfunction number is the lockout version, so 38-53 is the lockout after 38-13.
- Gas valve, flame, pressure switch, rollout and inverter codes need a technician.
Related questions
How do I read a Carrier furnace status code?
What does code 33 mean on a Carrier furnace?
What does code 31 mean on a Carrier furnace?
What does 18-11 mean on a Carrier Greenspeed heat pump?
Is there a Carrier EC error code on this page?
Need help with your system? Call (925) 999-4095 or book a visit. Repair diagnostics are $99, credited toward the repair. Installation assessments are free.
Further reading
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