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Carrier Furnace
Flashing Codes

What does a flashing light on a Carrier furnace mean?

It's a two-digit status code. Count the short flashes for the first digit and the long flashes for the second: 3 short and 3 long is code 33, a limit fault, often a dirty filter or blocked vent. Codes 13 and 14 are lockouts that reset on their own after three hours.

By Jason Strauss, founder of Answer3 · Updated October 21, 2026

How to Read the Code

Find the small window in the lower blower door. The status light is on the control board behind it.
Watch a full cycle. Count the short flashes (first digit), then the long flashes (second digit). There's a pause, then it repeats.
Write the code down before opening the door. Removing the door cuts power, and the light stops.
Match the code in the table below, then check it against the label on your own blower door.

Carrier Furnace Status Codes

Code	What it means	What to check
11	No previous code Normal. No faults are stored; stored codes clear after 72 hours.	Nothing.
12	Blower on after power-up Power came back during a call for heat, so the blower runs for 90 seconds.	Nothing, unless it keeps repeating.
13	Limit circuit lockout A limit, draft or rollout switch stayed open longer than 3 minutes, or tripped 10 times in a row. Resets itself after 3 hours.	See code 33.
14	Ignition lockout The burners failed to light or stay lit after repeated tries. Resets itself after 3 hours.	See code 34.
15	Blower motor lockout The blower didn't reach speed in two heating cycles in a row. Resets itself after 3 hours.	See code 41.
21	Gas heating lockout Gas valve wiring or the board's valve relay is at fault. Does not reset itself.	Call a technician.
22	Abnormal flame signal The board sees flame while the gas valve should be closed. The inducer keeps running until it clears.	Call a technician: a leaking or stuck gas valve is suspected.
23	Pressure switch did not open The pressure switch stayed closed when it should have opened.	Blocked pressure tubing or a stuck switch. Technician.
24	24-volt fuse open The low-voltage fuse on the board blew.	A short in thermostat or low-voltage wiring. Technician.
25	Model or setup error The model plug is missing or wrong, or a setup switch is in the wrong position.	Usually after a board swap or service visit. Technician.
31	High-heat pressure switch The high-heat pressure switch didn't close, or reopened.	Same checks as 32.
32	Low-heat pressure switch The low-heat pressure switch didn't close, or reopened. After 5 minutes the inducer rests 15 minutes and retries.	Vent pipe outside blocked by snow, leaves or a nest; strong wind. Otherwise a technician checks the inducer and tubing.
33	Limit circuit fault A limit, draft safeguard or flame rollout switch opened. Over 3 minutes it becomes lockout 13.	Dirty filter, closed vents or blocked ducts, a restricted vent pipe. A tripped rollout switch needs a technician.
34	Ignition proving failure The flame didn't prove. The board tries three more times, then locks out with code 14.	Gas turned on at the valve. A dirty flame sensor is the most common cause; a technician cleans it and checks gas pressure.
41	Blower motor fault The blower didn't reach 250 RPM, or stopped talking to the board.	Technician: blower motor, wiring or board.
43	Pressure switch mismatch The low-heat switch is open while the high-heat switch is closed.	Miswired or stuck switch, or blocked tubing. Technician.
45	Control circuitry lockout An internal board fault. Auto-resets after one hour.	Turn power off and on. If 45 returns, the control board needs replacing.

Steady, Off or Rapid Flashing

Light	Meaning
Off	No power. Check the furnace switch and breaker.
Steady on	The board has power and no fault.
Rapid flashing	The 120-volt wiring polarity is reversed. Technician.

Source: Carrier's service label (337803-201) in the 58CVA/58CVX Installation, Start-up, Operating and Service Instructions. Other Carrier models can use different numbers; your door label is the final word.

What You Can Safely Check

Most 33 and 32 codes come down to airflow or venting. Before you call anyone:

Replace the filter if it's gray or clogged. A choked filter is the most common cause of code 33.
Open the supply vents and make sure the return grille isn't blocked by furniture.
Look at the vent pipes outside for snow, ice, leaves or a nest.
Make sure the gas is on at the valve next to the furnace (handle in line with the pipe).

Then turn the furnace switch off for 30 seconds and back on. If the same code returns, call a technician. If you smell gas, leave the house and call your gas company from outside. Don't keep resetting a furnace that trips its flame rollout switch.

Give the tech the model first

Scan the furnace nameplate and Answer3 Vault saves the model, serial, age and the maker's parts list, so the technician can bring the right part on the first trip.

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Carrier Furnace Code FAQ

How do I reset a Carrier furnace after a lockout?

Codes 13, 14 and 15 reset on their own after three hours, and 45 after one hour. Turning the furnace switch off and on also clears a lockout. Fix the cause first, such as a dirty filter; code 21 never resets by itself.

Why does my Carrier furnace flash code 33?

A safety switch that watches for overheating or flames rolling out of the burner has opened. The most common cause is a clogged filter or closed supply vents. If the flame rollout switch tripped, call a technician and don't keep resetting it.

Can I read the code without opening the furnace?

Yes. Look through the small window in the lower blower door. Taking the door off cuts power through the door switch, so read and write down the code first.

Do all Carrier furnaces use these codes?

This list comes from Carrier's label for the 58CVA and 58CVX furnaces. Many Carrier and Bryant furnaces use the same short-then-long format, but the numbers can differ by model. Always match the code to the label on your own blower door.

Related Guides: How old is my Carrier? HVAC filter size by model Every brand: serial age decoder

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Carrier Furnace Flashing Codes