Expanded exact-code directory
Carrier gas furnace error codes
Carrier gas furnace codes as Carrier Residential HVAC (shareddocs) lists them, each with its meaning and the first safe check.
- 13Lockout. The limit, draft safeguard, flame rollout or
- 14Lockout. The furnace failed to ignite the gas
- 15Lockout. The blower failed to reach 250 RPM,
Carrier gas furnace code 11: meaning and exact next steps
11 means The control has no stored fault to report. Carrier explains that stored status codes are erased after 72 hours, or cleared by a technician, and that 11 is also what the control shows after a successful component test. When a technician replays stored codes, 11 marks the end of the list.
Open record Carrier gas furnace · exact codeCarrier gas furnace code 12: meaning and exact next steps
12 means Normal operation. The blower runs for 90 seconds when power is interrupted and restored during a call for heat, or if the call for heat drops during the blower on-delay. Carrier says a 12 that repeats every couple of minutes is probably a direct short in the pressure-switch circuits, the gas valve, the wiring to the gas valve or a humidifier coil.
Open record Carrier gas furnace · exact codeCarrier gas furnace code 23: meaning and exact next steps
23 means The low-heat or high-heat pressure switch was already made (closed) when the thermostat called for heat. The control flashes 23 until the switch opens, then starts the cycle.
Open record Carrier gas furnace · exact codeCarrier gas furnace code 33: meaning and exact next steps
33 means The limit, draft safeguard, flame rollout or blocked-vent switch is open, or the furnace is running in high-heat only because of 2 successive low-heat limit trips. The blower runs for 4 minutes or until the switch remakes, whichever is longer. If the switch stays open longer than 3 minutes the code becomes lockout 13. A flame rollout switch needs a manual reset.
Open record Carrier gas furnace · exact codeCarrier gas furnace code 34: meaning and exact next steps
34 means Flame was not sensed during the trial for ignition. The control repeats the ignition sequence 3 more times before going to lockout code 14. It can also mean the flame signal was lost during steady operation.
Open record Carrier gas furnace · exact codeCarrier gas furnace code 43: meaning and exact next steps
43 means The low-heat pressure switch did not make during a call for high heat while the high-heat switch did. The control keeps flashing 43; if the low-heat switch still has not closed after 5 minutes it shuts the unit down and waits 15 minutes before restarting.
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Every Carrier gas furnace code: what it means and what to do
Carrier gas furnace code 13
Lockout. The limit, draft safeguard, flame rollout or blocked-vent switch stayed open longer than 3 minutes, or there were 10 successive limit trips during high heat. The control resets itself after 3 hours. The flame rollout switch and the blocked-vent switch need a manual reset.
Turn the thermostat down, let the furnace cool, and check that the filter is clean and every supply and return register is open.
A code 13 means a safety switch tripped for a real reason, so do not keep resetting it. Carrier's flowchart works through the limit switch, the flame rollout switch, the blocked-vent safety switch and the draft safeguard switch, and asks about restricted vent pipe, wrong vent sizing and a missing elbow baffle. Excessive wind at the vent termination can also trip the blocked-vent switch. Replacing a switch before finding why it opened only repeats the lockout; a technician should find the airflow or venting cause.
Carrier gas furnace code 14
Lockout. The furnace failed to ignite the gas and prove flame in 4 attempts. The control resets itself after 3 hours. If the inducer motor is running at full speed during the lockout, Carrier says flame sense was lost 3 times within 60 minutes of gas-valve operating time, usually from flame rollout when the vent pipe has come apart inside the furnace or in a small enclosed closet.
Note whether the inducer fan is running during the lockout, and look for a disconnected vent pipe without touching it.
If the inducer is not running, Carrier sends you to code 34. If it is running at full speed, suspect flame rollout from a disconnected or damaged vent and stop using the furnace. Do not keep power-cycling to force another attempt; ignition problems are technician work.
Carrier gas furnace code 15
Lockout. The blower failed to reach 250 RPM, or failed to communicate with the furnace control within 30 seconds of turning on, in two successive heating cycles. The control resets itself after 3 hours.
Check that the furnace has power and that nothing is blocking the blower compartment or return air.
Carrier says to use its code 41 procedure. That procedure asks whether the blower wheel rubs the housing or is loose on the motor shaft, checks the 115-volt and 12-volt supply to the motor and the wiring between the control and the motor, and ends at replacing the blower motor or its control module, or the furnace control. It starts with removing the blower access panel, so it is technician work.
Carrier gas furnace code 21
Lockout. The main gas-valve relay on the control is stuck closed, or there is a mis-wire or short in the gas-valve wiring. Carrier notes the BLUE wire goes to the gas valve M terminal and the GREEN/YELLOW wire to the C terminal. The control does NOT reset itself.
Turn the furnace off at the switch and do not keep restoring power.
A code 21 that does not reset itself needs a technician. Carrier's flowchart first checks whether 21 still flashes with the thermostat lead disconnected, which points at a mis-wire or short in the gas-valve wiring. It then watches whether 21 starts when the low-heat or high-heat pressure switch makes: at low heat the answer is to replace the furnace control, and at high heat it points at the BLUE and GREEN wires to the gas valve being reversed. For an intermittent 21 it says to replace the furnace control, and if the problem persists after that, to contact your distributor. Do not adjust or bypass anything.
Carrier gas furnace code 22
The control sensed a flame signal while the gas valve was de-energized. The inducer keeps running until the fault clears.
Look for visible flame in the burner compartment through the sight glass only, without opening the furnace.
Carrier's flowchart begins by having the technician shut off the external manual gas valve and asking whether 22 stops flashing. The outcomes are replacing the gas valve or replacing the furnace control, depending on the answer. Treat a flame signal with the gas valve de-energized as a safety condition and call a technician.
Carrier gas furnace code 24
The 3-amp automotive-type fuse on the furnace control is open, which means there is a short in the low-voltage wiring.
Check whether the thermostat wiring has been disturbed or a new accessory (humidifier, thermostat) was just connected.
Carrier's flowchart replaces the fuse with a fuse of exactly 3 amps and then finds the short: it looks at the orange wire from the low-heat pressure switch, the blue wire to the gas valve, the humidifier, and loose or torn insulation on low-voltage wires. Using a larger fuse hides the short and risks the control.
Carrier gas furnace code 25
The control is missing its model plug (PL4), or has a setup-switch conflict. If 25 flashes only 4 times on power-up, the model plug is missing and the control is using the model stored in memory. If it flashes continuously, Carrier lists: no model plug and no stored model, a thermostat call with SW1-1 ON, a call with SW1-6 ON, both switches ON together, or two different furnace models twinned.
Note whether 25 flashed 4 times once at power-up or is flashing continuously.
This is a setup fault, common after a replacement control board is installed without the model plug. Carrier's flowchart moves the plug from the old control to the new one, checks each plug against the model-plug chart, and says two different-size furnaces cannot be twinned.
Carrier gas furnace code 31
The high-heat pressure switch or relay did not close, or reopened. On a call for high heat, if the switch has not made within 30 seconds of prepurge, or within 45 seconds after high heat was requested, the control flashes 31 and carries on; if it still has not made within the next 75 seconds, it shuts the unit down and keeps flashing 31 until the blower off-delay ends. Carrier notes that installations above 5,000 feet need a field-supplied high-altitude high-heat pressure switch, and a mis-wired gas valve can also cause this.
Look for anything blocking the exhaust and intake terminations outside, such as snow, ice, leaves or a nest.
The high-heat pressure switch proves the inducer is moving enough air. Carrier's flowchart runs through the switch and its wiring, the main wire harness, the inducer motor and wheel, the vent system, and the furnace control. Replace only what the check identifies, and never jumper the switch.
Carrier gas furnace code 32
The low-heat pressure switch did not close or reopened, or the low gas-pressure switch opened. If the switch has not made within 30 seconds of a call for heat, the control shows 32 until it closes; if it has not closed within 5 minutes it shuts down and waits 15 minutes before trying again. If it opens after the burners light, the control shuts down, runs the blower at low-heat airflow, and restarts, restricted to high heat if it opened within 5 minutes of ignition.
Check the exhaust and intake terminations outside for snow, ice or debris.
Code 32 points at the vent, the inducer or the switch circuit, and the guide also covers the low gas-pressure switch. Carrier's flowchart checks continuity across the low gas-pressure switch, whether the inducer motor runs, turns the right way and has a sound wheel firmly mounted, and the wiring from the control to the inducer and to the pressure switch. It names excessive restriction in the vent pipe, and leakage in the collector box or heat exchanger before the pressure tap, as causes, and ends at replacing the pressure switch, the inducer motor assembly, or the furnace control.
Carrier gas furnace code 41
The blower failed to reach 250 RPM, or failed to communicate with the furnace control within 30 seconds of being turned on or within 10 seconds during steady operation.
Confirm the furnace has power and that nothing is stuck against the blower compartment or the return air.
Carrier's flowchart runs 5 minutes of operation to see whether 41 appears, then checks whether the blower wheel rubs the housing, turns freely and is firmly on the motor shaft, and whether the connector pins and wires between the control and motor are intact. It measures 115 volts at the motor, the 12-volt DC supply on the red and green wires and the 5-volt serial signal. Its outcomes are replacing the whole blower motor or its control module (and inspecting a failed motor for water damage, including the A-coil and humidifier), repairing an open wire or harness, or replacing the furnace control.
Carrier gas furnace code 45
Lockout. The control detected a flame-sense circuit failure, a software check error or a gas-valve relay stuck open. It resets itself after 1 hour.
Turn the furnace off, wait an hour, and see whether it recovers without a repeat.
Carrier's guidance is direct: replace the variable-speed furnace control if the status code repeats. That is a technician repair, not a reset.