Carrier Furnace Error Codes: What Each Flash Means

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

Carrier Furnace Error Codes: What Each Flash Means

Short answer

Most Carrier gas furnaces flash a two digit code: count the short flashes for the first digit and the long flashes for the second. 33 is usually airflow and a dirty filter, 34 is usually the flame sensor, 31 is the venting or pressure switch, and 22 means gas is still burning when it should not be, which is the one to switch off for.

Carrier furnaces tell you what went wrong with a small light on the control board, and you can read it without taking anything apart. The trick is knowing that the flashes come in two kinds.

Everything on this page comes from Carrier’s own service literature: the troubleshooting guide for its two stage induced combustion furnaces, form 58-3T, and the installation and service instructions for the current 58SC0A and 58SC1A furnaces. Both use the same two digit system.

Before you start

What to carry: a torch and a pen. Ten minutes, and most of it is watching a light.

Gas or electric? These codes are for Carrier gas furnaces. A Carrier heat pump or electric air handler uses different lights and codes.

Read it before you open anything. There is a small window, the sight glass, in the lower blower door. Look through it first. On many boards the stored code is lost the moment the power is cut, and taking the blower door off cuts the power.

Bryant and Payne are made by the same company, and many of their furnaces use the same system. Whatever the brand, the chart printed on the label inside your own furnace door has the final word.

Two codes where you stop, not troubleshoot. Code 22 means flame is being sensed while the gas valve is supposed to be off. Carrier’s literature points to a stuck open or leaky gas valve. Turn the furnace off at its switch and close the gas to it. That is not a code to reset and watch.

If you smell gas at any point, leave the house and call from outside.

And code 33 with a tripped flame rollout switch means flame came out of the burners. Reset it once at most, and read why first: what a rollout switch is telling you.

How to read the light

Count the short flashes for the first digit, then the long flashes for the second. Three short and three long is code 33. Watch it cycle twice before you write it down.

Check 1Free, five minutes

Count the short flashes, then the long ones

Steady on. The control has power and is normal. No fault.

Off altogether. No power reaching the control. Check the furnace switch, the breaker, and that the blower door is fully shut, because a door switch cuts the power when it is open.

Rapid flashing with no pattern. Carrier’s literature points to the incoming power being wired the wrong way round. That is a wiring job.

Short and long flashes. A two digit code. Short flashes give the first digit, long flashes the second. Two short and three long is 23.

Code 11 means no previous fault. Carrier boards clear their stored code after two or three days, and many older red light boards also clear it when the power is interrupted.

Code 12 is normal after power returns during a call for heat. The blower runs for about ninety seconds on its own.

The codes, and what to check first

Code	What Carrier calls it	What to check first
11	No previous code	Nothing stored. Watch a heating cycle
12	Blower on after power up	Normal, it stops after about 90 seconds
13	Limit circuit lockout	Same causes as 33. Resets itself after 3 hours
14	Ignition lockout	Same causes as 34. Resets itself after 3 hours
21	Gas heating lockout	Control relay or gas valve wiring. Technician
22	Abnormal flame proving signal	Gas valve stuck open or leaking. Switch off
23	Pressure switch did not open	Blocked pressure tube, or switch stuck closed
24	Secondary voltage fuse is open	The 3 amp fuse, and a short in thermostat wiring
31	Pressure switch did not close or reopened	Blocked vent, tubing, inducer, wind
33	Limit circuit fault	Dirty filter or closed vents first
34	Ignition proving failure	Gas turned off, then the flame sensor
45	Control circuitry lockout	The control board itself

The four codes you can often clear yourself

Four codes that each have a free first check. Two of them come straight back if the real cause is left alone.

Check 2

Work the free check for your code

33, and 13 after it: the limit circuit. The furnace got too hot and shut itself down. Carrier’s list starts with a dirty filter or a restricted duct system. Change the filter, open every register, and watch a full cycle: why a furnace overheats and cuts out.

34, and 14 after it: ignition proving. The control did not sense a flame during the trial for ignition. After checking the gas is on at the furnace, the usual answer is a dirty flame sensor. Carrier gives a normal flame current of 4 to 6 microamps: how to clean a flame sensor safely.

31: the pressure switch did not close. The inducer could not prove the vent was clear. Check the pipes outside for snow, ice or a nest, then the little rubber tube to the switch: the five places to look.

24: the fuse. A 3 amp fuse on the board has blown, and Carrier says to fit only a 3 amp fuse. It blew because something shorted the low voltage wiring, often a thermostat wire, so find that before fitting a new one, or it blows again.

The codes that need a technician

Check 3

Know when to stop

21, gas heating lockout. Carrier points at the relay on the control that drives the gas valve, or a miswired or shorted valve wire.

22, flame with the valve off. A gas valve that does not close properly. Off at the switch, gas off, and a technician.

23, pressure switch did not open. Sometimes a blocked tube you can clear, but a switch stuck closed is a replacement part and has to be the right one.

45, control circuitry lockout. On current models the control resets itself after an hour and tries again. If it keeps coming back, the board is the part.

Anything that repeats after the free check. A code that clears and returns is telling you the cheap cause was not the real one.

Questions people ask

My light is amber, not red.

Carrier’s current controls use an amber light, and the codes read the same way. One difference: Carrier says a stored code on an amber light board is not erased when the power is interrupted.

The code I saw is not on this list.

Some models add codes of their own, especially two stage and variable speed furnaces. The label inside the blower door lists every code your board uses.

It shows 33 and the filter is new.

Then look at closed registers, a blocked return, and the blower. Carrier’s list for 33 also includes a loose blower wheel and a failing blower motor or capacitor.

My Carrier has a thermostat that shows the fault in words.

Infinity and other communicating systems report faults on the wall control instead of a flashing code. Read the message there.

It shows 13 or 14 and then starts working again hours later.

That is the three hour automatic reset Carrier builds in. The furnace is not fixed, it is trying again, and it will lock out again for the same reason.

Can I turn it off and on to clear the code?

You can, and it often gets the heat back. Write the code down first, because on many boards the power cycle wipes it and the next person has nothing to go on.

Sources: Carrier service literature: troubleshooting guide form 58-3T and the 58SC0A/58SC1A instructions