Carrier AC Error Codes Explained: Full List, Causes, and Fixes (2026)

Your Carrier system just stopped working – and now you’re staring at a blinking light or confusing error code.

Is it something simple… or an expensive repair?

Here’s the truth:
Most Carrier error codes point to specific, fixable problems – from clogged filters and airflow issues to ignition failures or communication faults.

But ignoring the wrong one?
That can turn a $50 fix into a $2,000 breakdown.

⚠️ Before You Panic – Check This First

Some of the most common Carrier error codes:

• Code 31 / 32 → Pressure or airflow problem
• Code 33 → Overheating (very common)
• Code 41 → Blower motor issue
• Code 45 → System lockout

Many of these can be diagnosed in minutes – if you know what to look for.

How To Read Carrier Blinking Lights

The green computer board inside uses a simple blinking language. The short flashes give you the first number. The long flashes give you the second number. For example, three short flashes and one long flash means Code 31. The computer uses this language to tell you what part is broken.

These codes are safety lockouts. The computer brain shuts the gas and power off to prevent the heavy machine from starting a house fire. Read our Carrier Furnace Blinking Red Light Codes guide to see the full secret light language. We have the complete Carrier AC error codes list ready for you.

If you’re seeing repeated system failures, it may not be just a code issue – check the AC not cooling properly guide to diagnose deeper problems.

Carrier Error Codes

Code	System Type	Error Name	What It Means	Common Causes	Severity	SEO Priority	User Intent
12	Furnace	Blower On After Power Up	Normal startup behavior	Power restored	Low	Low	Informational
13	Furnace	Limit Circuit Lockout	System overheated	Dirty filter, blocked vents	High	🔥 High	Fix
16	Infinity	Communication Fault	Indoor/outdoor units not communicating	Wiring, control board	High	🔥 High	Fix
17	Infinity	Outdoor Comm Loss	Outdoor unit disconnected	Loose wires, board issue	High	🔥 High	Fix
18	Infinity	Variable-Speed Fault	Blower motor issue	ECM motor failure	Medium	Medium	Fix
21	Furnace	Gas Heating Lockout	Gas issue detected	Valve, ignition failure	High	Medium	Fix
22	Furnace	Flame Signal Fault	Flame detected incorrectly	Dirty flame sensor	Medium	Medium	Fix
23	Furnace	Pressure Switch Fault	Switch didn’t open	Vent blockage	Medium	Medium	Fix
24	Furnace	Fuse Open	Electrical protection triggered	Short circuit	Medium	Medium	Fix
25	Furnace	Invalid Limit State	Limit switch logic error	Control board issue	Medium	Medium	Fix
31	Furnace	Pressure Switch Fault	Draft/venting issue	Blocked flue, inducer motor	🔥 Critical	🔥 VERY HIGH	Fix NOW
32	Furnace	Low Pressure Switch	Insufficient airflow	Clogged drain, vent issue	🔥 Critical	🔥 VERY HIGH	Fix NOW
33	Furnace	Limit Circuit Fault	Overheating condition	Dirty filter, airflow issue	🔥 Critical	🔥 VERY HIGH	Fix
34	Furnace	Ignition Failure	Burner won’t ignite	Igniter, gas supply	🔥 Critical	🔥 VERY HIGH	Fix
35	Furnace	Flame Rollout	Dangerous flame issue	Blocked heat exchanger	🚨 Emergency	🔥 VERY HIGH	Emergency
41	AC / Furnace	Blower Motor Fault	Fan not working properly	Capacitor, motor failure	High	🔥 High	Fix
43	AC	Low Airflow	Insufficient air circulation	Dirty filter, duct blockage	High	🔥 High	Fix
45	Furnace	Lockout	Too many failed attempts	Ignition/limit issues	High	🔥 High	Reset
47	System	Control Board Fault	Main board malfunction	Electrical failure	Medium	Medium	Replace
52	Heat Pump	High Temp Lockout	Overheating detected	Poor airflow	Medium	Medium	Fix
53	Infinity	Communication Error	System communication lost	Wiring, board	High	🔥 High	Fix
54	Heat Pump	Temp Sensor Fault	Sensor malfunction	Wiring, sensor failure	Medium	Medium	Fix
55	System	Lockout (Manual Reset)	Critical shutdown	Multiple faults	High	🔥 High	Reset

Carrier Error Codes 31 And 32

Why The Pressure Switch Fails

The machine must push toxic smoke out of your house safely through a white plastic pipe. The pressure switch makes sure the pipe is clear. The switch feels the air pushing through the plastic tube.

If a dead bird or heavy snow blocks the white pipe outside, the switch shuts the gas off. The machine refuses to choke your family with dangerous exhaust fumes. This is a very smart safety feature. A Carrier code 31 fix is incredibly common during heavy winter snowstorms.

Fix

We must test the rubber hoses and the plastic safety switch. Replacing a broken pressure switch costs between $150 and $300 depending on the specific furnace model. We clear the blocked white pipes and install a fresh new safety sensor.

If you try to bypass this safety switch, the toxic smoke will back up into the metal heating chamber. If ignored, you will pay over $2,500 to replace a completely cracked heat exchanger. You must fix the blocked pipe fast to protect the heavy metal parts.

Carrier Error Code 34

The Dirty Flame Sensor

The machine opens the gas valve and tries to spark a fire. A tiny metal rod sits in the flames to prove the fire is burning. This tiny part is the flame sensor.

This metal rod gets covered in dark black carbon soot over the winter. The soot builds up like a thick blanket. The computer cannot feel the fire through the thick black dirt. Carrier error code 34 means the machine turned the gas off because it thought the fire blew out.

Fix

We must pull the sensor out and scrub the tiny metal rod with a special soft pad. We do not use rough sandpaper because it ruins the delicate metal. Read our Furnace Ignitor Replacement Cost guide to see pricing for broken sparking parts. We make the metal shine like brand new.

Carrier Error Code 16

System Communication Failure

Carrier Infinity systems use digital signals to talk. They are very smart machines. The indoor wall screen must talk to the heavy green board constantly. They share secrets through thin colored wires.

Code 16 means the communication line is totally broken. A mouse might chew the thin wire in the dark basement. The machine goes completely deaf and blind.

Fix

We have to find the broken spot in the colored wire. Splicing broken communication wires costs between $150 and $300 depending on the hidden location. We connect the bare copper back together and wrap it in thick tape.

If you let the bare wires touch wet metal, a huge power surge will shoot into the main computer. If ignored, you will spend over $900 replacing the entire central logic board. You must repair broken wires immediately.

Carrier Error Codes 33, 43, 24, and 25

Limit Switch And Setup Faults

The limit switch stops the machine from melting. This is the meaning behind Code 33. A filthy clogged air filter traps the heat inside the metal box. The heat builds up fast and trips the safety switch.

The limit switch trips to save your house from a massive fire. Check the Energy.gov Furnaces page to read why changing filters saves you huge money.

Code 43 means the pressure switch is stuck open. The small rubber diaphragm inside the plastic switch is ripped. The machine will not start until the switch closes properly. Codes 24 and 25 mean the secondary voltage is wrong or the setup is bad. A blown fuse on the green board will trigger a Code 24 instantly. These are complicated electrical problems that require special testing meters.

Carrier Error Codes 52, 54, and 55

Gas Valve And Ignition Lockouts

These codes are very serious warnings. You must treat them with extreme caution. Code 54 means the machine tried to light the fire too many times and failed completely. It locks you out for three full hours to let the explosive gas clear out safely. This prevents a massive fireball in your basement.

Code 55 means the gas valve is doing something very wrong. The internal computer sees the gas valve opening when it should be closed. Code 52 means the gas valve is shut when it should be open. You must never try to touch heavy metal gas pipes by yourself. A small gas leak can destroy your entire home.

Carrier Hard Reset

Step 1 – Turn Off The Thermostat

You must stop the indoor computer from asking for heat. Go to your hallway screen and push the off button. Leave the fan setting alone.

Step 2 – Check The White Pipes

Walk outside and clear any heavy snow blocking the exhaust vents. Look inside the white plastic pipe for dead leaves or frozen ice blocks.

Step 3 – Change The Dirty Filter

Pulling out a solid gray dust filter fixes Code 33 instantly. Slide a fresh clean paper filter into the metal slot.

Step 4 – Flip The Breaker

Walk to your main electrical panel. Flip the heavy double breaker in the garage panel to clear the safety lockout. Wait five minutes and push the heavy switch back on.

Step 5 – Call A Professional

Turn the thermostat back to the heat setting. If the red code comes back, the physical metal part is completely dead. You must call for emergency backup.

Carrier Repair Cost Table

Problem / Error	Typical Repair	DIY Possible	Average Cost (USD)	High-End Cost	Urgency
Dirty air filter (Codes 13, 33, 43)	Replace filter	✅ Yes	$10 – $40	$50	Low
Flame sensor dirty (Code 22)	Clean sensor	✅ Yes	$80 – $150	$250	Medium
Igniter failure (Code 34)	Replace igniter	⚠️ Partial	$150 – $350	$600	High
Pressure switch issue (Codes 31, 32)	Replace switch / clear vent	⚠️	$150 – $400	$700	🔥 High
Blocked vent / flue	Cleaning / repair	❌	$200 – $800	$1,500	🔥 High
Blower motor failure (Code 41)	Replace motor	❌	$400 – $900	$1,800	🔥 High
Capacitor replacement	Replace capacitor	⚠️	$120 – $300	$500	Medium
Control board failure (Code 47)	Replace board	❌	$500 – $1,200	$2,000	🔥 High
Communication error (Codes 16, 17, 53)	Wiring / board fix	❌	$200 – $800	$1,500	High
Refrigerant leak	Leak repair + recharge	❌	$400 – $1,500	$3,000	🔥 High
Frozen evaporator coil	Defrost + fix airflow	⚠️	$150 – $600	$1,200	Medium
Heat exchanger issue (Code 35)	Replace exchanger	❌	$1,500 – $3,500	$6,000	🚨 Critical
Thermostat issue	Replace thermostat	✅ Yes	$100 – $300	$800	Low
Fuse / minor electrical	Replace fuse	⚠️	$100 – $250	$400	Low
Full system replacement	New HVAC system	❌	$5,000 – $12,000	$20,000+	🚨 Extreme

When You Should Call an HVAC Technician

You must call an expert when you smell rotten eggs or raw gas near the metal cabinet. Raw gas is incredibly dangerous. The red code comes back instantly after a hard breaker reset. This means the machine is totally locked down.

You see water leaking from the bottom of the machine. Water ruins the delicate green computer boards fast. You have a Carrier AC Error Code 41 showing on the wall. This points to a massive communication failure with the main blower motor. You must never open the burner compartment and touch high voltage wires or raw gas lines by yourself. Let our experts handle the heavy danger.

FAQ

How do I read Carrier furnace error codes?

Look through the clear plastic window on the bottom door to see the blinking red light. Count the short flashes for the first number and the long flashes for the second number.

What does Carrier error code 31 mean?

Code 31 means the pressure switch detects a blocked exhaust pipe. Heavy snow or a dead bird is choking the white plastic pipe outside your house.

How do I fix Carrier error code 34?

Code 34 is an ignition failure usually caused by a dirty flame sensor. A professional must remove the tiny metal rod and scrub the black carbon soot off the tip.

Can I reset my Carrier furnace to clear the codes?

Yes. You can flip the heavy circuit breaker off for five minutes to clear the computer memory. The code will come back immediately if the physical part is still broken.

Why is my Carrier furnace blowing cold air?

The system shut the hot gas burners off for safety but kept the fan running to cool the hot metal down. Check the blinking light to see which safety switch tripped.

Conclusion

Sitting in a freezing cold house is a terrible experience for your family. Carrier error codes like 31 and 34 are severe warnings that a physical part stopped working safely. You must act quickly to change your dirty filters and clear your exhaust pipes before the system locks you out in the bitter cold. You should never touch the dangerous raw gas valves by yourself. Call our friendly local experts for safe and fast HVAC services. Use our Contact Us page or call us directly to schedule a fast damage inspection. We will replace the broken switches and get your house completely warm again right now.