HeatingCodes

Carrier furnace status code 33: limit circuit fault

By Jason Dearmin · Last reviewed November 14, 2026 · How we check facts

Short answerOn Carrier's 2-stage condensing furnace control, status code 33 means a limit switch or flame rollout switch in the safety circuit is open. The blower runs for at least four minutes. If the switch stays open more than three minutes, the code turns into limit circuit lockout 13.

What code 33 means

Carrier's service procedures (SP05-59) list code 33 as Limit circuit fault: it indicates that a limit switch or flame rollout switch is open. These switches are safety devices. The furnace shuts the burners down when one of them opens, and it will not fire again until the circuit closes.

On the LED, status codes are two digits. The first digit is the number of short flashes and the second digit is the number of long flashes, so code 33 is three short flashes and then three long flashes.

What the furnace does while code 33 shows

Carrier's check list for code 33

The manufacturer's table says to check for the following. This is the service document's list, written for a technician:

Why a rollout switch deserves extra respect

Goodman's service manual for its 96% furnaces describes the same family of switches: the primary limit guards against overheating from too little air passing over the heat exchanger, and the rollout limits "guard against burner flames not being properly drawn into the heat exchanger." In other words, an open rollout switch can be a combustion or venting problem, not just a dirty filter. That is the main reason not to keep restarting a furnace that repeats this code.

Safety Never jumper, bypass or tape over a limit or rollout switch. If you smell gas, leave the house and call your gas utility. If a carbon monoxide alarm sounds, get everyone outside and call 911.

Only the checks in the list below are homeowner tasks. Everything else on the manufacturer list above needs a technician.

Safe homeowner checks for Carrier furnace code 33

  1. Check the air filterTurn the thermostat to off. Look at the furnace air filter and replace it if it is clogged. The manufacturer lists a dirty filter first among the causes of an open limit.
  2. Open supply and return ventsMake sure supply registers and the return grille are open and not blocked by furniture or rugs, because a restricted duct system can overheat the heat exchanger.
  3. Check outdoor vent and intake pipesFrom outside, look at the furnace vent and combustion-air terminations and clear obvious snow, ice or debris. Do not climb on roofs or open the vent pipes.
  4. Restart once and watchSet the thermostat to heat. If code 33 or 13 comes back, stop and call a heating technician rather than resetting repeatedly.

Frequently asked questions

Is Carrier code 33 an emergency?

Not by itself. It is a safety shutdown, and the furnace is doing its job by stopping. Treat it as urgent if it repeats, if the code changes to 13, or if you notice a gas smell, soot, a yellow or orange burner flame, or a carbon monoxide alarm.

What is the difference between code 33 and code 13?

Code 33 is the fault while a limit or rollout switch is open for under three minutes. Code 13 is the lockout that follows when the switch has been open longer than three minutes. Carrier says the control resets code 13 automatically after three hours.

Does code 33 mean I need a new furnace?

No. The code points at the safety circuit, and the causes in Carrier's list range from a dirty filter to a loose blower wheel or a failed switch. A technician can find which one it is.

Sources

Related

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Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.