The readout is the part people get wrong, so start here. Carrier's amber status LED does not flash a simple count. It flashes the first digit as short pulses, pauses, then flashes the second digit as long pulses. One short and four long is code 14, an ignition lockout. Because the numbering is built that way, every classic Carrier code has two digits and the list starts at 11 — there is no code 1, 2 or 3 on these boards.
That also settles a myth worth naming. Carrier's classic amber-LED furnaces have no code 44: the numbering runs 41, 42, 43, then jumps to 45. Lists claiming a Carrier code 44 for undersized ductwork are describing a four-LED variable-speed board Carrier used around 1999, which counted digits from a yellow and a green light rather than short and long flashes, and whose numbering does not map onto anything on a modern furnace. If your board has one amber light, that older list does not apply to you.
To read the code, remove the main door only and look through the sight glass — Carrier's instructions specifically tell you not to pull the blower access panel. Newer Infinity-series furnaces from roughly 2022 onward add a three-digit display showing a major and a minor code together, and some meanings changed on those boards, so do not carry a classic definition across to a code written with a decimal point. Codes vary by model and the label inside the panel is the authority: where this page and that label disagree, the label wins. Our Carrier furnace repair page covers what we stock, and you can reach us here.
Carrier furnace codes, decoded
| Code | What it means | Safe? | Try first | When to call |
|---|---|---|---|---|
Continuous on | The control has 24-volt power and nothing to report. On a Carrier this steady amber light is the normal standby state. | keep running | Nothing. A solid light here is good news. | Not needed. |
Continuous off | No power at the board — check the 115-volt supply and the 24-volt secondary. | turn it off | Check the breaker, the service switch and that the door is closed. | If power is present and the light stays dark. |
Rapid flashing | Line voltage polarity is reversed, or on twinned furnaces the transformers are out of phase. | turn it off | Nothing at home — the supply wiring needs correcting. | Yes. Typical after an install or electrical work. |
11 | No previous code stored. The board has nothing in memory. | keep running | Nothing. This is what a healthy history looks like. | Not needed. |
12 | Blower on after power up — a normal 90-second run following a power interruption. | keep running | Nothing. Expect it after an outage. | Not needed unless it repeats constantly. |
13 | Limit circuit lockout after the limit stayed open past three minutes, or ten successive high-heat trips. Resets on its own after three hours. | turn it off | Fit a clean filter and open any registers that are shut. | If it returns once airflow is restored. |
14 | Ignition lockout — the furnace gave up trying to light. Auto-resets after three hours. | turn it off | Confirm gas is reaching the house using another gas appliance. | Same day when the house is cold. The classic no-heat code. |
15 | Blower motor lockout after the motor failed to reach speed or stopped reporting across two cycles. Auto-resets after three hours. | turn it off | Listen for a motor humming without moving air, then shut it down. | Right away. A stalled motor overheats. |
21 | Gas heating lockout. This one does not auto-reset — the board has stopped trying until someone intervenes. | turn it off | Nothing at home. Do not sit and cycle the breaker on this one. | Yes. A code that refuses to clear itself is telling you something. |
22 | Abnormal flame-proving signal — the board is seeing flame behaviour it does not expect from the gas valve state. | call now | Switch the furnace off and leave the gas shutoff as it is. | Immediately. Flame out of sequence is a safety matter. |
23 | Pressure switch did not open when it should have — the switch is stuck closed. | turn it off | Nothing safe at home. The switch guards the venting. | Right away. |
24 | Secondary voltage fuse is open. Something downstream shorted and took the fuse with it. | turn it off | Nothing. Replacing the fuse alone rarely ends the problem. | Yes — the short needs finding, not just the fuse. |
31 | High-heat pressure switch or its relay did not close, or opened again during the cycle. | turn it off | Check the outside terminations for snow, ice or a nest. | If the vents are clear and it still shows 31. |
32 | Low-heat pressure switch did not close, or reopened while running. | turn it off | Look for a blocked condensate trap or a drain backing up. | If the drain runs freely and the code stays. |
33 | Limit circuit fault. Left open past three minutes this becomes lockout 13, and if the rollout switch is what opened, it needs a manual reset. | turn it off | New filter first. If a rollout button on the burner box has popped, do not press it — stop there. | Immediately if a rollout switch tripped; otherwise once airflow is ruled out. |
34 | Ignition proving failure. The board gets three more attempts before it escalates to lockout 14. | turn it off | Check the gas supply, then leave it to run its retries. | Soon. This is code 14 in the making. |
41 | Blower motor fault — the motor is reporting a problem short of a full lockout. | turn it off | Note any new noise or vibration to describe on the phone. | Soon, before it becomes lockout 15. |
42 | Inducer motor fault. The venting fan is not performing the way the board expects. | turn it off | Nothing at home. | Soon. An inducer struggling is on its way out. |
45 | Control circuitry lockout — the board has found a fault in itself. Auto-resets after one hour. | turn it off | Allow one power cycle. If it comes straight back, stop. | Yes. Repeated 45s generally end in a board. |
The codes that usually mean a real repair
Codes 34 and 14 — the ignition sequence, then the lockout
These two codes are the same story at different stages. Code 34 is the furnace failing to prove flame and getting ready to try again; code 14 is what you find the next morning once it used up its attempts and locked out for three hours. The parts are almost always the hot surface igniter at $200–$450 or the flame sensor at $150–$300. Worth knowing which you are hearing: if the inducer runs and nothing glows, look at the igniter, and if burners light then die a few seconds later, the flame sensor is the usual culprit.
Codes 23, 31 and 32 — venting, drains and pressure switches
Carrier's pressure switch codes describe what the switch saw, not necessarily a broken switch, and the distinction saves money. Code 23 means it was stuck closed when it should have been open; 31 and 32 mean it never closed on the high or low heat stage. On condensing Carriers the usual cause is a condensate trap silted up over a few seasons, a drain backing up, or side-wall terminations icing during a freeze-thaw week off the lake. Clearing or replacing a blocked trap runs $150–$350, while the switch itself sits in the $250–$500 band.
Codes 41, 42 and 15 — the two motors
Carrier separates the blower and the inducer into their own codes, which makes quoting straightforward. Code 42 is the inducer, the small fan that pulls combustion gas through the heat exchanger, and a draft inducer motor replacement runs $400–$900. Codes 41 and 15 are the indoor blower, where a fault warning has become a lockout, and a blower motor is $500–$1,500 depending on whether it is a standard motor or a variable-speed ECM. Because 15 auto-resets after three hours, a failing blower can masquerade as an intermittent problem for weeks before anyone catches it in the act.
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Common questions
How do I count a Carrier furnace status code?
Watch for two different flash lengths. The amber LED gives the first digit as a series of short flashes, pauses, then gives the second digit as a series of long flashes. Three short flashes followed by four long ones is code 34. Because the code is built from two digits this way, the list begins at 11 and no single-digit Carrier codes exist. Watch several full cycles before deciding, and read the light through the sight glass with only the main door removed — Carrier's instructions say not to pull the blower access panel to do it.
Is a solid amber light on my Carrier furnace a problem?
No. On a Carrier, a continuous amber light means the control has 24-volt power and has nothing to report, which is exactly what you want to see in standby. This is worth stating plainly because the opposite is true on some other brands built by the same parent company, where a steady light means the furnace has locked out and a pulsing heartbeat means healthy. If someone has told you a solid light is bad, they were describing a different board.
What does Carrier error code 44 mean?
There isn't one on a modern Carrier furnace. The classic amber-LED numbering runs 41, 42, 43 and then jumps straight to 45, with no 44 in between. Lists that give a Carrier 44 are reproducing a four-LED variable-speed board from around 1999 that used an entirely different counting method, or they are quoting a fan coil code rather than a furnace code. If your board has a single amber status light, treat any 44 you find online as belonging to another appliance.
Which Carrier lockouts clear themselves?
Most of them, on their own schedule. Codes 13, 14 and 15 auto-reset after three hours, and code 45 resets after one hour. Code 21, the gas heating lockout, does not auto-reset at all — that one is deliberate, and it is the board declining to try again unattended. A furnace surviving a cold snap on three-hourly retries is still broken, and it will fail properly on the coldest night. Our furnace repair service runs a 24/7 line with no overtime surcharge if it has already got that far.
My Infinity control shows no alert but the furnace is misbehaving. Why?
Because the wall control does not surface everything the board logs. The Infinity control uses the same numbers as the furnace board, but several soft faults — the pressure switch and ignition proving codes among them — do not raise a banner at the thermostat even though the board recorded them. A quiet wall control is not proof that nothing happened. It is also worth checking which device a number came from, since the same number can mean different things on a fan coil or an outdoor unit than it does on the furnace — the outdoor numbers are on the Carrier AC and Infinity code guide.