Carrier Furnace error codes
30 Carrier furnace codes and problems, each with ranked causes, safe homeowner checks and honest repair costs. Count the flashes or read the code on your control board, then find it below. Legends vary by board revision, so confirm against the label inside your unit's door. Bryant uses the same control boards — see Bryant furnace codes.
Of these, 29 need a professional repair and 1 is usually safe to check yourself.
| Code | What it means | Severity |
|---|---|---|
| Code 12 | Carrier Furnace Code 12 means power was interrupted during heating. Causes, safe checks, fixes and repair costs for US homeowners. | Call a pro |
| Code 13 | Carrier furnace Code 13 means a limit circuit lockout. Causes: dirty filter, blocked vents, bad blower. Fixes cost $0 DIY to $600+. | Call a pro |
| Code 14 | Carrier Furnace Code 14 means ignition lockout after failed heat trials. Causes, safe checks, technician diagnosis and repair costs $0-$600. | Call a pro |
| Code 21 | Carrier Furnace Code 21 means a gas heating lockout from a shorted valve relay or mis-wired gas valve. Causes, fixes and pro repair costs inside. | Call a pro |
| Code 22 | Carrier Furnace Code 22 means flame is sensed with the gas valve off. Causes, safe checks, technician diagnosis and repair costs explained. | Call a pro |
| Code 23 | Carrier Furnace Code 23 means the pressure switch stayed closed before the inducer started. Causes, safe checks, fixes & repair costs. | Call a pro |
| Code 24 | Carrier Furnace Code 24 means the 3A low-voltage fuse is blown from a 24V wiring short. Causes, fixes, and repair costs for US homeowners. | Call a pro |
| Code 31 (pressure switch) | Carrier furnace flashing code 31 (pressure switch/inducer fault)? What it means, causes ranked by likelihood, safe checks, and repair costs. | Call a pro |
| Code 32 | Carrier Furnace Code 32 means the low-stage pressure switch did not close or reopened. Causes, fixes and repair costs from $0 DIY to $1,200+. | Call a pro |
| Code 33 | Carrier furnace flashing code 33 (limit circuit fault)? What it means, the causes ranked by likelihood, safe checks you can do, and repair costs. | Call a pro |
| Code 34 | Carrier furnace Code 34 means ignition proving failure. Causes, safe checks and pro fixes — flame sensor, gas valve, $0 DIY to $600 repair. | Call a pro |
| Code 41 | Carrier Furnace Code 41 signals a blower motor fault. Learn causes, safe checks, diagnosis and repair costs from $0 DIY to $700 for a new motor. | Call a pro |
| Code 42 | Carrier Furnace Code 42 means an inducer motor fault. Learn the causes, safe checks, technician diagnosis and repair costs from $0 DIY to $1,200. | Call a pro |
| Code 43 | Carrier Furnace Code 43 means a pressure switch calibration fault. Causes: venting, tubing, inducer, switch. Fixes and US repair costs inside. | Call a pro |
| Code 44 | Carrier Furnace Code 44 means a blower motor calibration fault on variable-speed boards. Causes, safe checks, fixes and repair costs explained. | Call a pro |
| Code 45 | Carrier furnace Code 45 means a control circuitry lockout from flame-sense, software, or gas-valve relay faults. Causes, fixes and repair costs. | Call a pro |
| Blower not running | Carrier furnace blower not running? Causes from bad capacitors to door switches, plus fixes and repair costs from $0 DIY to $1,200. | Call a pro |
| Blower won't shut off | Carrier furnace blower running non-stop? Causes include fan setting, bad limit switch, or a stuck fan relay, plus DIY checks and repair costs. | DIY-friendly |
| Blowing cold air | Carrier furnace blowing cold air? Common causes are thermostat fan settings, ignition faults, overheating and flame-sensor issues, plus fixes and costs. | Call a pro |
| Clicking but not starting | Carrier furnace clicking but not starting? Causes include a cracked igniter, dirty flame sensor, or weak inducer draft. Fixes and costs from $0 to $1,200. | Call a pro |
| Flame sensor problems | Carrier furnace flame sensor problems cause short cycling and no heat. Learn the causes, safe checks and repair costs ($0 DIY reset to $1,200 pro). | Call a pro |
| Ignition lockout | Carrier furnace ignition lockout means failed ignition after repeated tries. See causes, safe checks, fixes and repair costs from $0 DIY to $1,200. | Call a pro |
| Keeps shutting off | Carrier furnace keeps shutting off? Causes include dirty filters, flame sensor, limit switch and pressure switch faults, plus fixes and US repair costs. | Call a pro |
| Leaking water | Carrier furnace leaking water? Causes include clogged condensate lines, bad drains, and flue issues, plus fixes and repair costs from $0 to $3,000+. | Call a pro |
| Loud bang on startup | Carrier furnace loud bang on startup usually means delayed ignition or duct oil-canning. Learn causes, safe checks, fixes and repair costs. | Call a pro |
| Pressure switch stuck open | Carrier furnace pressure switch stuck open: blocked vent, weak inducer or condensate clog causes plus fixes and repair costs ($0 DIY–$1,200). | Call a pro |
| Runs constantly but not enough heat | Carrier furnace runs nonstop but the house stays cold. Causes from dirty filters to failing heat exchangers, plus DIY checks, fixes and repair costs. | Call a pro |
| Short cycling | Carrier furnace short cycling? Learn the top causes—dirty filter, overheating, flame sensor, oversizing—plus safe checks, fixes and repair costs. | Call a pro |
| Won't ignite | Carrier furnace won't ignite? Common causes include a dirty flame sensor, bad igniter, gas or pressure switch faults, plus DIY checks and repair costs. | Call a pro |
| Won't turn on | Carrier furnace won't turn on? Common causes include a tripped breaker, dead thermostat batteries, blown fuse or bad door switch. Fixes and costs inside. | Call a pro |
Don't see your code? Look it up — every search we can't answer goes into the queue for the next guide.