HVAC Code Lookup

Carrier fault codes

28 documented codes for Carrier furnaces, each cited to the manufacturer's own manual. Find your code in the table, then jump to what it means, the likely causes, what you can safely check, and when to call a technician.

Carrier, Bryant and Payne are all ICP/Carrier (Carrier Global) brands and share the same furnace control boards and the same 2-digit LED status-code system. A Bryant 926 or Payne PG92 will flash the same code numbers as the equivalent Carrier 58-series furnace.

Looking it up by flash count?

If you counted LED flashes rather than reading a code number, these are the codes that start with that many flashes:

  • 1 flashes: 10.1 (L1 polarity fault), 11 (No previous code), 12 (Blower on after power up), 13 (Limit circuit lockout), 14 (Ignition lockout), 14.2 (Flame lost lockout), 14.3 (Flame lost lockout), 15 (Blower motor lockout)
  • 2 flashes: 21 (Gas heating lockout), 22 (Abnormal flame-proving signal), 23 (Pressure switch did not open), 24 (The 3-amp secondary voltage fuse on the control board is blown, which means there is a short somewhere in the 24 V low-voltage wiring), 25 (Model selection or setup error)
  • 3 flashes: 31 (Pressure switch did not close, or reopened during the cycle), 32 (Low-heat pressure switch did not close on a call for low heat, or opened during low heat), 33 (Limit circuit fault), 34 (Ignition proving failure)
  • 4 flashes: 41 (Blower motor fault), 42 (Inducer motor fault), 43 (The low-heat pressure switch is open while the high-heat pressure switch is closed - a contradictory pressure switch state on a two-stage furnace), 45 (Control circuitry lockout), 45.1 (Control failure - flame circuit fault, memory mismatch, or sequence error inside the control board), 45.2 (Control failure - the gas valve relay on the control board will not close), 45.3 (Control failure - EEPROM memory issue on the control board), 46.1 (Momentary loss of power)

Furnace codes

CodeMeaningSeverity
LED offStatus LED is completely dark - no flashing at allThe control board has no powerWarning
LED on solidStatus LED glows steady, no flashingNormalStatus
rapid flashVery fast continuous flashing with no pause between flashesLine voltageHard lockout
10.1Rapid flashing LED; the 3-digit display reads 10.1L1 polarity faultHard lockout
111 short flash, 1 long flashNo previous codeStatus
121 short flash, 2 long flashesBlower on after power upStatus
131 short flash, 3 long flashesLimit circuit lockoutSoft lockout
141 short flash, 4 long flashesIgnition lockoutSoft lockout
14.2Major code 14 flashed on the LED (1 short, 4 long); 14.2 on the 3-digit displayFlame lost lockoutSafety fault
14.3Major code 14 flashed on the LED (1 short, 4 long); 14.3 on the 3-digit displayFlame lost lockoutSafety fault
151 short flash, 5 long flashesBlower motor lockoutSoft lockout
212 short flashes, 1 long flashGas heating lockoutHard lockout
222 short flashes, 2 long flashesAbnormal flame-proving signalSafety fault
232 short flashes, 3 long flashesPressure switch did not openWarning
242 short flashes, 4 long flashesThe 3-amp secondary voltage fuse on the control board is blown, which means there is a short somewhere in the 24 V low-voltage wiringHard lockout
252 short flashes, 5 long flashesModel selection or setup errorWarning
313 short flashes, 1 long flashPressure switch did not close, or reopened during the cycleWarning
323 short flashes, 2 long flashesLow-heat pressure switch did not close on a call for low heat, or opened during low heatWarning
333 short flashes, 3 long flashesLimit circuit faultSoft lockout
343 short flashes, 4 long flashesIgnition proving failureWarning
414 short flashes, 1 long flashBlower motor faultWarning
424 short flashes, 2 long flashesInducer motor faultWarning
434 short flashes, 3 long flashesThe low-heat pressure switch is open while the high-heat pressure switch is closed - a contradictory pressure switch state on a two-stage furnaceWarning
454 short flashes, 5 long flashesControl circuitry lockoutSoft lockout
45.1Major code 45 on the LED (4 short, 5 long); 45.1 on the 3-digit displayControl failure - flame circuit fault, memory mismatch, or sequence error inside the control boardSoft lockout
45.2Major code 45 on the LED (4 short, 5 long); 45.2 on the 3-digit displayControl failure - the gas valve relay on the control board will not closeSafety fault
45.3Major code 45 on the LED (4 short, 5 long); 45.3 on the 3-digit displayControl failure - EEPROM memory issue on the control boardSoft lockout
46.1Major code 46 on the LED (4 short, 6 long); 46.1 on the 3-digit displayMomentary loss of powerStatus

Carrier furnace LED Off: The control board has no power

WarningShown as: Status LED is completely dark - no flashing at all

The control board has no power. The manual's first step is to verify 115 VAC is reaching the board at L1 and L2 and that the transformer is delivering 24 VAC at SEC-1 and SEC-2.

Manual wording: “CONTINUOUS OFF - Check for 115VAC at L1 & L2, & 24VAC at SEC-1 & SEC-2.”

Documented for: 58MCB, 58MVP, 58UVB and most Carrier 58-series furnaces

Likely causes, most common first

  1. No 115 VAC at the furnace (breaker off, service switch off)
  2. Blower access door not seated, so the door interlock switch is holding power off
  3. Blown transformer or open 24 VAC circuit

What you can safely check yourself

  • Make sure the furnace blower door is fully closed and latched - the door switch cuts all power when it is open
  • Check that the furnace service switch (looks like a light switch near the furnace) is ON
  • Check the breaker labeled furnace in your electrical panel

When to call a technician

If the door is seated and the breaker and service switch are on but the board is still dark, the transformer, door switch, or board itself needs a technician with a meter.

Sources

Carrier furnace LED On Solid: Normal

StatusShown as: Status LED glows steady, no flashing

Normal. The control has 24 VAC power and no fault is stored or active.

Manual wording: “CONTINUOUS ON - Control has 24VAC power.”

Documented for: 58MCB, 58MVP, 58UVB and most Carrier 58-series furnaces

Likely causes, most common first

  1. Normal standby or normal operation

What you can safely check yourself

  • Nothing to do - a steady light means the board is powered and healthy

When to call a technician

If the furnace is not heating even though the light is steady, the problem is more likely the thermostat or its wiring than the furnace control.

Sources

Carrier furnace Rapid Flash: Line voltage

Hard lockoutShown as: Very fast continuous flashing with no pause between flashes

Line voltage (115 VAC) polarity is reversed at the furnace. The control cannot prove flame with reversed polarity, so the furnace will not run.

Manual wording: “RAPID FLASHING - Line voltage (115VAC) polarity reversed. If twinned, refer to twinning kit instructions.”

Documented for: 58MCB, 58MVP, 58UVB and most Carrier 58-series furnaces

Likely causes, most common first

  1. Hot and neutral swapped at a junction box, outlet, or the furnace itself
  2. On twinned furnaces, incorrect low-voltage (24 V) transformer phasing

When to call a technician

Reversed line-voltage polarity is an electrical wiring fault. A technician (or electrician) has to find and correct the crossed hot and neutral - this is not a homeowner repair.

Sources

Carrier furnace code 10.1: L1 polarity fault

Hard lockoutShown as: Rapid flashing LED; the 3-digit display reads 10.1

L1 polarity fault. The polarity of the incoming 115 V power is reversed and the furnace will not operate.

Manual wording: “10.1 L1 POLARITY FAULT - Rapid flash LED. Polarity of incoming 115V power is reversed.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Line voltage (115 V) hot and neutral reversed at a junction
  2. If units are twinned, improper low-voltage (24 V) transformer phasing

When to call a technician

Correcting 115 V polarity means opening junction boxes and working on live wiring - call a licensed HVAC technician or electrician.

Source

Carrier furnace code 11: No previous code

StatusShown as: 1 short flash, 1 long flash

No previous code. The control has no fault stored - either nothing has failed or the stored code has aged out. Stored codes erase automatically after 72 hours.

Manual wording: “11 NO PREVIOUS CODE - Stored status codes are erased automatically after 72 hours or as specified above.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB and most Carrier 58-series furnaces

Likely causes, most common first

  1. Normal - no fault in memory
  2. A previous fault was cleared by a power interruption or by the 72-hour timeout

What you can safely check yourself

  • Nothing to fix - run the furnace through a full heating cycle and see whether a real code appears

When to call a technician

If the furnace is misbehaving but only shows 11, have a technician watch a live heating cycle to catch the fault as it happens.

Sources

Carrier furnace code 12: Blower on after power up

StatusShown as: 1 short flash, 2 long flashes

Blower on after power up. Normal operation - if furnace power is interrupted and restored while the thermostat is calling for heat, the blower runs for 90 seconds.

Manual wording: “12 BLOWER ON AFTER POWER UP - (115 VAC or 24 VAC) - Blower runs for 90 seconds, if unit is powered up during a call for heat (R-W/W1 closed)”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB and most Carrier 58-series furnaces

Likely causes, most common first

  1. Power was interrupted and restored during a call for heat (R to W closed)
  2. The thermostat call ended during the blower on-delay period

What you can safely check yourself

  • Nothing to fix - this is normal after a power blip or after you flip the furnace switch back on

When to call a technician

If code 12 keeps appearing without any power outages, have a technician check for a loose 115 V connection or a failing door switch.

Sources

Carrier furnace code 13: Limit circuit lockout

Soft lockoutShown as: 1 short flash, 3 long flashes

Limit circuit lockout. The limit switch, draft safeguard, flame rollout, or blocked-vent switch has stayed open longer than 3 minutes (or the furnace tripped the limit 10 times in a row on high heat). The control locks out and auto-resets after 3 hours.

Manual wording: “13 LIMIT CIRCUIT LOCKOUT - Lockout occurs if the limit, or flame rollout switch is open longer than 3 minutes or 10 successive limit trips occurred during high-heat. Control will auto reset after 3 hours.”

Documented for: 58SC0A, 58SC0B, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. The furnace repeatedly overheated - almost always an airflow problem (see code 33 for the full cause list)
  2. Flame rollout switch tripped, which requires manual reset by a technician
  3. Defective limit switch or connections

What you can safely check yourself

  • Check the air filter and replace it if it is dirty - restricted airflow is the number one cause
  • Make sure supply registers and return grilles are open and not blocked by furniture or rugs
  • Check that the furnace door is fully closed

When to call a technician

Code 13 means the furnace has been overheating. Even if a new filter clears it, have a technician verify why the limit was tripping - a flame rollout trip in particular is a combustion problem that must be diagnosed before the furnace is put back in service.

Sources

Carrier furnace code 14: Ignition lockout

Soft lockoutShown as: 1 short flash, 4 long flashes

Ignition lockout. The furnace failed to ignite the gas and prove flame in four attempts. The control locks out and auto-resets after 3 hours.

Manual wording: “14 IGNITION LOCKOUT - System failed to ignite gas and prove flame in 4 attempts. Control will auto-reset after 3 hours. See status code 34.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Igniter or flame sensor problem (see code 34 for the manual's full list)
  2. Low inlet gas pressure or a closed manual gas valve
  3. Defective gas valve
  4. Loss of control ground continuity

What you can safely check yourself

  • Confirm other gas appliances in the house are working, so you know the gas supply itself is on
  • Turn the furnace off at the service switch for a minute and back on once to force one clean retry

When to call a technician

Ignition lockout is a gas-side fault. Diagnosing the igniter, flame sensor, gas valve, and gas pressure requires a technician - do not attempt to clean or move the flame sensor yourself.

Sources

Carrier furnace code 14.2: Flame lost lockout

Safety faultShown as: Major code 14 flashed on the LED (1 short, 4 long); 14.2 on the 3-digit display

Flame lost lockout. The flame signal was lost three times after the heating blower on-delay. The control auto-resets after 3 hours.

Manual wording: “14.2 FLAME LOST LOCKOUT - Flame signal was lost 3 times after heating blower on delay. Control will auto-reset after 3 hours. See status code 34.3.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Incorrect manifold pressure or gas firing rate
  2. Gas inlet pressure fluctuations
  3. Flame sensing problem - see code 34

What you can safely check yourself

  • Check that the furnace filter is clean and vents are open, since airflow problems can disturb the flame

When to call a technician

Losing an established flame repeatedly is a combustion problem. Have a technician check manifold pressure, gas supply pressure, and the flame sensing circuit before running the furnace.

Source

Carrier furnace code 14.3: Flame lost lockout

Safety faultShown as: Major code 14 flashed on the LED (1 short, 4 long); 14.3 on the 3-digit display

Flame lost lockout. The flame signal was lost seven times during a single heat request.

Manual wording: “14.3 FLAME LOST LOCKOUT - Flame signal was lost 7 times during a single heat request. See status code 34.2 to 34.3.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Incorrect manifold pressure and gas firing rate
  2. Gas inlet pressure fluctuations
  3. Flame sensing problem - see codes 34.2 and 34.3

What you can safely check yourself

  • Check that the furnace filter is clean and supply and return vents are open

When to call a technician

Repeated flame loss inside one heat call needs a technician to check gas pressure and the combustion setup. Do not keep resetting the furnace to force it to run.

Source

Carrier furnace code 15: Blower motor lockout

Soft lockoutShown as: 1 short flash, 5 long flashes

Blower motor lockout. The variable-speed blower failed to reach 250 RPM, or failed to communicate with the control within 30 seconds of being switched on, in two successive heating cycles. Auto-resets after 3 hours.

Manual wording: “15 BLOWER MOTOR LOCKOUT - Indicates the blower failed to reach 250 RPM or the blower failed to communicate within 30 seconds after being turned ON in two successive heating cycles.”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Failed blower motor or motor control module
  2. Loose or damaged blower motor wiring/communication harness

What you can safely check yourself

  • Check that the blower door is fully seated - the door switch removes power to the blower

When to call a technician

A variable-speed blower motor fault is a technician job; the motor, its module, and its harness all have to be tested.

Source

Carrier furnace code 21: Gas heating lockout

Hard lockoutShown as: 2 short flashes, 1 long flash

Gas heating lockout. The control detected 24 VAC on the gas valve when it should not be there. This lockout does NOT auto-reset.

Manual wording: “21 GAS HEATING LOCKOUT - Control will NOT auto reset. Check for: - Mis-wired gas valve. - Defective control (valve relay).”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Stuck-closed gas valve relay on the control board
  2. Mis-wired or shorted gas valve wire

When to call a technician

Code 21 means the control can no longer guarantee it can shut the gas valve off. Shut the furnace off at the service switch and call a technician - this one does not clear on its own.

Sources

Carrier furnace code 22: Abnormal flame-proving signal

Safety faultShown as: 2 short flashes, 2 long flashes

Abnormal flame-proving signal (false flame). The control senses flame while the gas valve is de-energized. The inducer will keep running until the fault clears.

Manual wording: “22 ABNORMAL FLAME-PROVING SIGNAL - Flame is proved while gas valve is de-energized. Inducer will run until fault is cleared.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Leaky gas valve
  2. Stuck-open gas valve

When to call a technician

This code means gas may be burning when the control has commanded the valve closed. Turn the furnace off at the service switch and call a technician immediately. Do not touch or attempt to test the gas valve.

Sources

Carrier furnace code 23: Pressure switch did not open

WarningShown as: 2 short flashes, 3 long flashes

Pressure switch did not open. The control expected the vent pressure switch to be open at the start of the cycle and it was still closed.

Manual wording: “23 PRESSURE SWITCH DID NOT OPEN - Check for: - Obstructed pressure tubing. - Pressure switch stuck closed.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Obstructed pressure tubing
  2. Pressure switch stuck closed

When to call a technician

The pressure switch is a combustion safety device. A technician needs to inspect the tubing and switch - never bypass or jumper a pressure switch.

Sources

Carrier furnace code 24: The 3-amp secondary voltage fuse on the control board is blown, which means there is a short somewhere in the 24 V low-voltage wiring

Hard lockoutShown as: 2 short flashes, 4 long flashes

The 3-amp secondary voltage fuse on the control board is blown, which means there is a short somewhere in the 24 V low-voltage wiring.

Manual wording: “24 SECONDARY VOLTAGE FUSE IS OPEN - Check for: - Short circuit in secondary voltage (24V) wiring including thermostat leads.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Short circuit in the 24 VAC secondary wiring, including the thermostat leads

When to call a technician

Replacing the fuse without finding the short just blows the new fuse. A technician needs to isolate the shorted thermostat or accessory wire.

Sources

Carrier furnace code 25: Model selection or setup error

WarningShown as: 2 short flashes, 5 long flashes

Model selection or setup error. The model plug (PL4) is missing or wrong, or a setup switch is in the wrong position. If the code flashes only 4 times at power-up, the control is running on the model selection stored in memory.

Manual wording: “25 MODEL SELECTION OR SETUP ERROR - Either Indicates the model plug (PL4) is missing or incorrect or setup switch "SW1-1" or "SW1-6" is positioned improperly.”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Model plug PL4 missing or incorrect (common after a replacement control board)
  2. Setup switch SW1-1 or SW1-6 left ON
  3. Two different furnace models twinned together

When to call a technician

This is a setup fault that appears after service work. The technician who last worked on the furnace needs to install the correct model plug and reset the setup switches.

Source

Carrier furnace code 31: Pressure switch did not close, or reopened during the cycle

WarningShown as: 3 short flashes, 1 long flash

Pressure switch did not close, or reopened during the cycle. On single-stage furnaces this is the main vent pressure switch; on two-stage furnaces code 31 is the high-heat pressure switch or relay. If the switch stays open longer than 5 minutes the inducer shuts off for 15 minutes before retrying.

Manual wording: “31 PRESSURE SWITCH DID NOT CLOSE OR REOPENED - If open longer than five minutes, inducer shuts off for 15 minutes before retry.”

Documented for: 58SC0A, 58MCB (single-stage); 58MVP, 58UVB high-heat pressure switch (two-stage)

Likely causes, most common first

  1. Restricted vent, or the intake/exhaust pipe blocked by snow, ice, leaves or a nest
  2. Plugged condensate drain
  3. Excessive wind at the vent termination
  4. Disconnected or obstructed pressure tubing
  5. Defective inducer motor or low inducer voltage
  6. Defective or out-of-calibration pressure switch
  7. Improper vent sizing or inadequate combustion air supply

What you can safely check yourself

  • Go outside and check the furnace intake and exhaust pipes for snow, ice, leaves, or a bird/insect nest, and clear anything blocking them
  • Check the condensate drain line and trap for a clog or standing water
  • Check that the air filter is clean

When to call a technician

If the vent pipes are clear and the drain is not clogged, the inducer motor, pressure switch, or tubing needs a technician. Never jumper a pressure switch to make the furnace run.

Sources

Carrier furnace code 32: Low-heat pressure switch did not close on a call for low heat, or opened during low heat

WarningShown as: 3 short flashes, 2 long flashes

Low-heat pressure switch did not close on a call for low heat, or opened during low heat. If it opens within 5 minutes after ignition, the next heating cycle is forced to high heat.

Manual wording: “32 LOW-HEAT PRESSURE SWITCH DID NOT CLOSE OR REOPENED - Indicates the low-heat pressure switch input failed to close on a call for low-heat, or opened during low-heat.”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Improper vent sizing
  2. Plugged condensate drain
  3. Low inlet gas pressure (if a low gas pressure switch is used)
  4. Excessive wind
  5. Restricted combustion air supply
  6. Improper pressure switch wiring
  7. Failed or out-of-calibration pressure switch
  8. Water in the vent piping from a sagging pipe
  9. Disconnected or obstructed pressure tubing

What you can safely check yourself

  • Check outdoor intake and exhaust pipe terminations for snow, ice, or debris
  • Check the condensate drain and trap for a clog
  • Replace a dirty air filter

When to call a technician

Vent sizing, sagging vent pipe, and pressure switch calibration are all technician diagnostics. Do not bypass the switch.

Source

Carrier furnace code 33: Limit circuit fault

Soft lockoutShown as: 3 short flashes, 3 long flashes

Limit circuit fault. The high-limit switch, draft safeguard, flame rollout, or blocked-vent shutoff switch is open - the furnace is overheating or venting badly. The blower runs for 4 minutes or until the switch remakes. If the switch stays open more than 3 minutes the code changes to lockout 13.

Manual wording: “33 LIMIT CIRCUIT FAULT - Indicates the limit, or flame rollout is open. Blower will run for 4 minutes or until open switch remakes whichever is longer.”

Documented for: 58SC0A, 58SC0B, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Dirty filter or restricted duct system
  2. Loose blower wheel
  3. Defective switch or connections
  4. Defective blower motor or capacitor
  5. Inadequate combustion air supply (flame rollout switch open)
  6. Restricted vent or improper vent sizing
  7. Excessive wind
  8. Improper gas input adjustment

What you can safely check yourself

  • Check and replace the air filter - a clogged filter is the most common cause
  • Make sure supply registers and return air grilles are open and unblocked
  • Confirm the furnace door is fully seated
  • Check outdoor vent terminations for blockage

When to call a technician

If the code returns after a filter change, the limit or rollout switch is tripping for a reason a technician must diagnose. The flame rollout switch requires manual reset and must never be reset without finding out why it tripped.

Sources

Carrier furnace code 34: Ignition proving failure

WarningShown as: 3 short flashes, 4 long flashes

Ignition proving failure. Flame was not sensed during the trial for ignition. The control will retry three more times before going to ignition lockout (code 14).

Manual wording: “34 IGNITION PROVING FAILURE - Control will try three more times before lockout #14 occurs.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Low inlet gas pressure
  2. Gas valve defective or turned off / manual shut-off valve closed
  3. Defective hot surface igniter
  4. Oxide buildup on the flame sensor
  5. Loss of control ground continuity - the green/yellow wire must be connected to the furnace sheet metal
  6. Flame sensor grounded or misplaced
  7. Inadequate flame carryover or rough ignition

What you can safely check yourself

  • Confirm other gas appliances in the house still work so you know gas service is on
  • Check that the furnace door is fully closed

When to call a technician

Cleaning the flame sensor, checking microamp flame current, and testing the igniter all require opening the burner compartment on a live gas appliance. Call a technician.

Sources

Carrier furnace code 41: Blower motor fault

WarningShown as: 4 short flashes, 1 long flash

Blower motor fault. The blower failed to reach 250 RPM, or failed to report back to the control within the allowed time (30 seconds after start, or 10 seconds during steady operation).

Manual wording: “41 BLOWER MOTOR FAULT - Indicates the blower failed to reach 250 RPM or the blower failed to communicate within the prescribed time limits.”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Failed blower motor or motor module
  2. Loose blower motor wiring or communication connection
  3. Blower wheel jammed or seized

What you can safely check yourself

  • Make sure the blower access door is fully closed and latched
  • Turn the furnace off at the service switch for a minute, then back on once, to force a fresh start

When to call a technician

Testing an ECM/variable-speed blower motor and its module requires a technician. Repeating this code usually means the motor or module is failing.

Source

Carrier furnace code 42: Inducer motor fault

WarningShown as: 4 short flashes, 2 long flashes

Inducer motor fault. The inducer did not start within 20 seconds of a call for heat, its RPM is outside the valid range, or the RPM signal was lost for 5 seconds during operation.

Manual wording: “42 INDUCER MOTOR FAULT - Indicates the inducer has not started within 20 seconds after a call for heat, the inducer motor RPM is outside its valid range of operation, or the inducer RPM signal was lost for 5 seconds during operation.”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Improper vent sizing
  2. Restricted combustion air supply
  3. Failed inducer motor
  4. Improper motor wiring

What you can safely check yourself

  • Check the outdoor intake and exhaust pipes for snow, ice, or debris blocking them

When to call a technician

The inducer motor and its wiring have to be tested by a technician. A furnace that cannot run its inducer cannot vent combustion gases safely.

Source

Carrier furnace code 43: The low-heat pressure switch is open while the high-heat pressure switch is closed - a contradictory pressure switch state on a two-stage furnace

WarningShown as: 4 short flashes, 3 long flashes

The low-heat pressure switch is open while the high-heat pressure switch is closed - a contradictory pressure switch state on a two-stage furnace.

Manual wording: “43 LOW-HEAT PRESSURE SWITCH OPEN WHILE HIGH-HEAT PRESSURE SWITCH IS CLOSED”

Documented for: 58MVP, 58UVB and other variable-speed two-stage Carrier furnaces

Likely causes, most common first

  1. Low inlet gas pressure (if a low gas pressure switch is used)
  2. Plugged condensate drain
  3. Improper pressure switch wiring
  4. Water in the vent piping from a sagging pipe
  5. Stuck-open low-heat pressure switch
  6. Disconnected or obstructed pressure tubing

What you can safely check yourself

  • Check the condensate drain line and trap for a clog or standing water
  • Check the outdoor vent terminations for blockage

When to call a technician

Pressure switch wiring and vent piping slope are technician diagnostics. Never jumper a pressure switch.

Source

Carrier furnace code 45: Control circuitry lockout

Soft lockoutShown as: 4 short flashes, 5 long flashes

Control circuitry lockout. The board detected an internal failure and locks out, auto-resetting after 1 hour.

Manual wording: “45 CONTROL CIRCUITRY LOCKOUT - Auto-reset after 1 hour lockout due to: - Flame sense circuit failure. - Gas valve relay stuck open. - Software check error.”

Documented for: 58SC0A, 58MCB, 58MVP, 58UVB

Likely causes, most common first

  1. Flame sense circuit failure
  2. Gas valve relay stuck open
  3. Software check error

What you can safely check yourself

  • Turn the furnace off at the service switch for a minute and back on once - the manual says resetting power clears this lockout

When to call a technician

If code 45 comes back after a power reset, the manual's own instruction is to replace the control board - that is a technician job.

Sources

Carrier furnace code 45.1: Control failure - flame circuit fault, memory mismatch, or sequence error inside the control board

Soft lockoutShown as: Major code 45 on the LED (4 short, 5 long); 45.1 on the 3-digit display

Control failure - flame circuit fault, memory mismatch, or sequence error inside the control board.

Manual wording: “45.1 CONTROL FAILURE - flame circuit fault, memory mismatch or sequence error.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Internal control board failure

What you can safely check yourself

  • Turn the furnace off at the service switch for a minute and back on once - the manual says to cycle power

When to call a technician

The manual says that if code 45 repeats after a power cycle, replace the control. That is a technician job.

Source

Carrier furnace code 45.2: Control failure - the gas valve relay on the control board will not close

Safety faultShown as: Major code 45 on the LED (4 short, 5 long); 45.2 on the 3-digit display

Control failure - the gas valve relay on the control board will not close.

Manual wording: “45.2 CONTROL FAILURE - gas valve relay will not close.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Failed gas valve relay on the control board

What you can safely check yourself

  • Turn the furnace off at the service switch and leave it off until a technician arrives

When to call a technician

A gas valve relay that will not close means the board can no longer control gas flow reliably. Shut the furnace off and call a technician; the manual's fix is to replace the control.

Source

Carrier furnace code 45.3: Control failure - EEPROM memory issue on the control board

Soft lockoutShown as: Major code 45 on the LED (4 short, 5 long); 45.3 on the 3-digit display

Control failure - EEPROM memory issue on the control board.

Manual wording: “45.3 CONTROL FAILURE - EEPROM memory issue.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Corrupted or failed memory on the control board

What you can safely check yourself

  • Turn the furnace off at the service switch for a minute and back on once

When to call a technician

If the code repeats after cycling power, the manual says to replace the control board.

Source

Carrier furnace code 46.1: Momentary loss of power

StatusShown as: Major code 46 on the LED (4 short, 6 long); 46.1 on the 3-digit display

Momentary loss of power. Heating stops and restarts on its own once the power fluctuation is resolved.

Manual wording: “46.1 MOMENTARY LOSS of power - Heating operation will stop and will restart once the power fluctuation is resolved.”

Documented for: 58SC0B/58SC1B

Likely causes, most common first

  1. Brownout or brief power interruption to the furnace

What you can safely check yourself

  • Nothing to fix if you had a power blip
  • If it happens often, check that the breaker is fully seated and the furnace service switch is not loose

When to call a technician

Frequent 46.1 codes with no utility outages point to a loose 115 V connection or failing door switch - have a technician check it.

Source

How old is this Carrier?

Age changes what a fault code means for you. The same failure is a routine repair on a six-year-old unit and the end of the line on a twenty-year-old one. Your Carrier serial number has the build date in it.

Decode your Carrierserial number →

Manuals used for this page