Carrier Furnace & AC Error Codes

Below is a complete list of Carrier furnace and air conditioner diagnostic error codes (also applies to Bryant, Payne, Heil, Day & Night). Each code includes what it means, safe DIY checks you can try, when to call a professional, and estimated repair costs.

How to Read Carrier Error Codes

Locate the diagnostic LED visible through the small sight glass on the furnace access panel. The yellow LED flashes first (first digit), pauses, then the green LED flashes (second digit). Count each set of flashes to determine the two-digit code. Do NOT turn off power while reading codes, as this clears the stored error.

LED Location: Visible through the small sight glass on the lower access panel of the furnace. Some models have two LEDs (yellow and green) on the control board itself.

Code Format: Two-digit code: first digit = yellow LED flashes, second digit = green LED flashes (e.g., Code 2-1 means 2 yellow flashes followed by 1 green flash)

Safety Warning

1 emergency code(s) require immediate professional attention. 8 high-urgency code(s) should be addressed promptly. If you smell gas, hear unusual sounds, or see sparks, turn off the system and call a professional immediately.

Quick Navigation — 16 Error Codes

Code 1-1 Code 1-2 Code 1-3 Code 2-1 Code 2-2 Code 2-3 Code 2-4 Code 3-1 Code 3-3 Code 3-4 Code 1-4 Code 4-1 Code 4-2 Code 4-5 Rapid LED Flash (continuous) LED Off (no light)

Carrier Code 1-1: No previous error code

Low Urgency

The control board has no stored error codes. Status codes are erased when power to the control is interrupted. This is a normal status indicating the system has been reset or has not encountered any faults since last power cycle.

Common Causes

  • Power was recently restored to the furnace
  • Control board was reset or replaced
  • System is operating normally with no faults

DIY Troubleshooting Steps

  1. This is a normal status — no action needed if your furnace is working properly
  2. If the furnace is not working despite showing 1-1, check your thermostat settings and ensure it is calling for heat

Call a professional when: The furnace is not producing heat despite this normal status code — there may be an issue the board is not detecting.

Carrier Code 1-2: Blower on after power up

Low Urgency

The blower motor runs for 90 seconds if the unit is powered up during an active call for heat. This is a safety feature, not an error. The furnace is clearing residual heat from the heat exchanger.

Common Causes

  • Furnace was powered on while the thermostat was calling for heat
  • Power outage recovery during a heating cycle
  • Breaker was reset while heat was being requested

DIY Troubleshooting Steps

  1. Wait 90 seconds — the blower should stop and the furnace should begin a normal heating cycle
  2. Verify your thermostat is set correctly and calling for heat

Call a professional when: The blower continues to run beyond 90 seconds without the furnace starting a heating cycle, or if this code persists after multiple reset attempts.

Carrier Code 1-3: Limit or flame roll-out switch lockout

High Urgency

The furnace has locked out due to the high-temperature limit switch or flame roll-out switch tripping repeatedly. The control will auto-reset after 3 hours. This is a serious safety code indicating the furnace is overheating or flames are escaping the burner compartment.

Estimated repair cost: $150 – $600

Common Causes

  • Dirty or clogged air filter restricting airflow and causing overheating
  • Blocked or restricted ductwork reducing airflow through the heat exchanger
  • Defective blower motor or capacitor preventing proper air circulation
  • Cracked heat exchanger allowing flames to roll out

DIY Troubleshooting Steps

  1. Check and replace the air filter immediately — a clogged filter is the most common cause of overheating
  2. Ensure all supply and return vents throughout the home are open and not blocked by furniture
  3. Look for any visible obstructions in the flue or exhaust pipe

Call a professional when: The code returns after replacing the filter and ensuring vents are open. Repeated flame roll-out can indicate a cracked heat exchanger, which is a serious safety hazard involving potential carbon monoxide exposure.

Carrier Code 2-1: Gas heating lockout

High Urgency

The furnace has entered a hard lockout due to a gas heating failure. The control will NOT auto-reset — manual intervention is required. This means the furnace attempted to ignite multiple times and failed, or the gas valve circuit has a problem.

Estimated repair cost: $200 – $600

Common Causes

  • Mis-wired gas valve connection
  • Defective gas valve not opening properly
  • Defective control board sending incorrect signals to the gas valve
  • Gas supply interrupted (shut-off valve closed, empty propane tank, or utility outage)

DIY Troubleshooting Steps

  1. Verify the gas supply is turned on — check the manual shut-off valve on the gas line near the furnace (handle should be parallel to the pipe)
  2. If you have propane, check that the tank is not empty
  3. Try resetting the furnace by turning power off for 30 seconds, then back on

Call a professional when: The lockout persists after confirming gas supply is on and resetting the furnace. Gas valve and wiring issues require a licensed technician. Never attempt to repair gas valve wiring yourself.

Carrier Code 2-2: Abnormal flame-proving signal

Emergency

The control board is detecting a flame signal at an unexpected time, either when the gas valve should be off or with a signal that is outside normal parameters. This can indicate a dangerous condition where gas is flowing when it should not be.

Estimated repair cost: $200 – $650

Common Causes

  • Leaking or stuck-open gas valve allowing gas to flow when valve is commanded off
  • Faulty flame sensor providing false readings to the control board
  • Short circuit in the flame sensing wiring
  • Defective control board misinterpreting the flame signal

DIY Troubleshooting Steps

  1. If you smell gas, leave the home immediately and call your gas company or 911 — do NOT flip any switches
  2. Turn off the gas supply to the furnace at the manual shut-off valve and call a professional

Call a professional when: This code should always be evaluated by a professional. A stuck-open gas valve is a serious safety hazard that can lead to gas accumulation and potential explosion.

Carrier Code 2-3: Pressure switch did not open

Medium Urgency

The pressure switch circuit remained closed when the inducer motor was not running, or the switch did not open as expected during the control sequence. This indicates the pressure switch may be stuck in the closed position.

Estimated repair cost: $150 – $400

Common Causes

  • Pressure switch stuck in closed position due to mechanical failure
  • Short circuit in the pressure switch wiring
  • Obstruction in the pressure tubing holding back-pressure on the switch
  • Defective pressure switch contacts welded shut

DIY Troubleshooting Steps

  1. Inspect the small rubber tubing connected to the pressure switch for kinks, cracks, or water blockage
  2. Check that the exhaust vent pipe is not blocked by debris, ice, or animal nests

Call a professional when: A stuck-closed pressure switch typically needs to be replaced by a technician. The switch is a safety device that should not be bypassed under any circumstances.

Carrier Code 2-4: Secondary voltage fuse is open

Medium Urgency

The low-voltage (24V) fuse on the control board has blown. This fuse protects the control board from short circuits in the thermostat wiring or low-voltage accessories.

Estimated repair cost: $100 – $300

Common Causes

  • Short circuit in the thermostat wiring (common during thermostat installation or replacement)
  • Defective or shorted-out thermostat
  • Short in the humidifier, electronic air cleaner, or other 24V accessory wiring
  • Damaged low-voltage wiring (rodent damage, nail through wire, pinched wire)

DIY Troubleshooting Steps

  1. If you recently installed a new thermostat, double-check that all wires are connected to the correct terminals and no bare wires are touching
  2. Look for any visible damage to the thin thermostat wires between the furnace and the thermostat

Call a professional when: The fuse blows again after replacement. Repeated blown fuses indicate a short circuit in the wiring that must be found and repaired. A technician can trace the short safely.

Carrier Code 3-1: Pressure/draft safeguard switch did not close

Medium Urgency

The pressure switch, draft safeguard switch, auxiliary limit switch, or blocked vent switch failed to close (or reopened) during operation. If the switch stays open for more than 5 minutes, the inducer motor shuts off for 15 minutes before retrying.

Estimated repair cost: $150 – $500

Common Causes

  • Blocked or restricted exhaust vent pipe (ice, bird nests, leaves, debris)
  • Failed or weak inducer motor not generating enough draft
  • Cracked or disconnected pressure switch hose
  • Clogged condensate drain (on high-efficiency 90%+ furnaces) causing water backup

DIY Troubleshooting Steps

  1. Inspect the exhaust vent pipe outside your home for visible blockages such as ice, snow, leaves, or animal nests
  2. Check the condensate drain line and drain trap for clogs — pour warm water through to clear any blockage
  3. Listen for the inducer motor (small motor near the top of the furnace) — it should start running when heat is called for

Call a professional when: The vent is clear and the inducer motor runs but the code persists. This often indicates a weak inducer motor, failed pressure switch, or a cracked heat exchanger creating a draft imbalance.

Carrier Code 3-3: Limit or flame roll-out switch is open

High Urgency

The high-temperature limit switch or flame roll-out switch is currently open (tripped). If the switch remains open for more than 3 minutes, the code escalates to 1-3 (lockout). The flame roll-out switch requires a manual reset.

Estimated repair cost: $150 – $600

Common Causes

  • Dirty air filter causing overheating due to restricted airflow
  • Defective blower motor or bad capacitor preventing proper airflow
  • Blocked or closed supply registers and return grilles
  • Inadequate combustion air supply or cracked heat exchanger

DIY Troubleshooting Steps

  1. Replace the air filter immediately if it appears dirty or has not been changed in over 3 months
  2. Open all supply and return vents in the home — do not close more than 20% of vents
  3. Check that the blower fan is spinning when the furnace is running — listen for the fan motor

Call a professional when: The limit switch keeps tripping after filter replacement and vent clearing. Recurring overheating may indicate a blower motor failure, bad capacitor, or a cracked heat exchanger, all of which require professional repair.

Carrier Code 3-4: Ignition proving failure

High Urgency

The furnace ignited but the flame was not proven (detected) by the flame sensor within the trial-for-ignition period, OR the flame was established but then lost. The control will retry three more times before entering lockout (code 1-4). If flame is lost after the trial period, the blower runs for a 90-second recycle delay.

Estimated repair cost: $100 – $350

Common Causes

  • Dirty flame sensor covered in oxidation buildup (most common cause)
  • Weak or failing igniter not producing enough heat to ignite gas
  • Low gas pressure causing weak or intermittent flame
  • Cracked flame sensor ceramic insulator grounding the sensor

DIY Troubleshooting Steps

  1. A dirty flame sensor is the number one cause of this code — if you are comfortable, turn off power, remove the flame sensor (single screw), and gently clean the metal rod with fine steel wool or emery cloth, then reinstall
  2. Verify gas supply is fully on and other gas appliances in the home are working

Call a professional when: Cleaning the flame sensor does not resolve the issue, or if the furnace ignites briefly then shuts down repeatedly. This could indicate low gas pressure, a failing igniter, or gas valve problems.

Carrier Code 1-4: Ignition lockout

High Urgency

The furnace has entered a hard lockout after failing to prove ignition after multiple retry attempts. The control will NOT auto-reset. This follows repeated code 3-4 failures.

Estimated repair cost: $150 – $400

Common Causes

  • Failed hot surface igniter (cracked or worn out)
  • Dirty or defective flame sensor not detecting the flame
  • Gas valve not opening or delivering insufficient gas
  • Gas supply issue (shut-off valve closed, low gas pressure)

DIY Troubleshooting Steps

  1. Reset the furnace by turning the power off for 30 seconds, then back on
  2. Verify gas supply is on and other gas appliances in the home work
  3. Check and clean the flame sensor if accessible (turn off power first)

Call a professional when: The lockout occurs again after reset. A technician can test the igniter amperage draw, verify gas pressure, and check the flame sensor microamp signal to identify the failing component.

Carrier Code 4-1: Low-stage heating lockout (two-stage models)

Medium Urgency

On two-stage furnaces, the low-stage heating has locked out due to repeated ignition failures on the low-fire setting. The furnace may still attempt high-stage operation.

Estimated repair cost: $150 – $450

Common Causes

  • Dirty flame sensor not detecting the lower flame properly
  • Gas pressure slightly low, affecting the weaker low-stage flame more than high stage
  • Partially clogged burner reducing flame quality at low stage
  • Control board two-stage valve driver issue

DIY Troubleshooting Steps

  1. Clean the flame sensor with fine steel wool or emery cloth (turn off power first)
  2. Replace the air filter if dirty to ensure proper airflow at all stages

Call a professional when: The code persists after cleaning the flame sensor. A technician needs to check gas manifold pressure at both stages and verify the two-stage gas valve operation.

Carrier Code 4-2: High-stage heating lockout (two-stage models)

High Urgency

On two-stage furnaces, the high-stage heating has locked out due to repeated ignition failures on the high-fire setting. This code is less common since higher gas flow is usually easier to ignite.

Estimated repair cost: $200 – $600

Common Causes

  • Gas valve high-stage solenoid failure
  • Insufficient gas supply unable to sustain high-stage flame
  • Dirty flame sensor not reading the flame signal accurately
  • Control board or wiring issue with the high-stage valve circuit

DIY Troubleshooting Steps

  1. Clean the flame sensor (turn off power first)
  2. Verify gas supply is fully on and no other high-demand gas appliances are running simultaneously

Call a professional when: This code requires professional diagnosis. A technician must measure gas pressure at the high-stage setting and test the two-stage gas valve solenoid.

Carrier Code 4-5: Control circuitry lockout

High Urgency

An internal control board failure has been detected. The control will NOT auto-reset. This typically indicates the control board itself has a fault in its circuitry.

Estimated repair cost: $400 – $1,200

Common Causes

  • Defective control board (failed component on the circuit board)
  • Power surge or lightning strike damage to the board
  • Intermittent wiring short causing the board to malfunction
  • Age-related degradation of control board components

DIY Troubleshooting Steps

  1. Try resetting the furnace by turning power off for 60 seconds, then back on
  2. Check for any signs of burn marks, melted components, or damaged wiring on the control board (turn off power and remove the access panel)

Call a professional when: This code almost always requires a control board replacement. A technician can verify the board has failed and source the correct replacement board for your model.

Carrier Rapid LED Flash (continuous): Line voltage polarity reversed

High Urgency

The 115V AC line voltage wiring to the furnace has reversed polarity (hot and neutral wires are swapped). This is an electrical wiring issue that prevents the furnace from operating safely.

Estimated repair cost: $100 – $250

Common Causes

  • Hot and neutral wires reversed at the furnace junction box
  • Outlet or disconnect wired incorrectly (common after electrical work)
  • Faulty extension cord or power source (if applicable)
  • Wiring error at the electrical panel

DIY Troubleshooting Steps

  1. If the furnace was recently serviced or new electrical work was done, this is likely the cause — call the electrician or HVAC technician who did the work
  2. Do NOT attempt to rewire the furnace yourself unless you are a licensed electrician

Call a professional when: Always call a professional for this code. Reversed polarity is an electrical hazard that can damage the control board and create shock risk. An electrician or HVAC technician needs to correct the wiring.

Carrier LED Off (no light): No power to furnace control board

Medium Urgency

The diagnostic LED is completely off, indicating no electrical power is reaching the furnace control board.

Estimated repair cost: $0 – $300

Common Causes

  • Tripped circuit breaker at the electrical panel
  • Furnace power switch turned off (looks like a light switch, usually on or near the furnace)
  • Blown fuse on the control board
  • Disconnected or damaged power wiring to the furnace

DIY Troubleshooting Steps

  1. Check the circuit breaker labeled for the furnace at your electrical panel — reset it if tripped
  2. Look for the furnace power switch (usually a standard light switch on the furnace or on a nearby wall) and make sure it is in the ON position
  3. Check the outdoor disconnect if applicable

Call a professional when: The breaker keeps tripping after being reset, or the LED remains off after confirming power is on. This may indicate an internal electrical fault.

Need Carrier Repair in Central Texas?

Texas Temp Masters provides expert HVAC repair for Carrier , Bryant, Payne, Heil, Day & Night, and all major brands in Killeen, Waco, Temple, and surrounding areas. Call (817) 704-0706 for fast, reliable service, or contact us online.

Error code information cross-referenced from manufacturer documentation, HVAC/appliance professional resources, and verified repair databases. Codes can vary by specific model and control board revision. Always verify against your unit's diagnostic label or owner's manual. Repair costs are estimates based on national averages. Last updated February 2026.

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