Code 33: Limit or flame roll-out switch is open
Homeowner checks
The most-searched Carrier code, and the manual is specific: dirty filter or restricted ducts, loose blower wheel, defective blower motor or capacitor, bad switch or connections — or the flame roll-out switch open, which needs a manual reset and a reason. Open longer than 3 minutes and the code becomes 13.
From the table: Two-digit status codes — short flashes, then long flashes — source: Carrier 58YAV Service section - status code table (read the document, fetched 2026-10-30). Covers: Carrier 58-series and their Bryant/Payne twins. First digit = number of short flashes; second digit = number of long flashes. Code 33 is 3 short, pause, 3 long.
Code 33 says a switch in the limit circuit is open. That circuit holds two different kinds of switch. The limit switch opens when the furnace overheats — an airflow story: Carrier's manual lists a dirty filter or restricted duct system, a loose blower wheel, a defective blower motor or capacitor, a bad switch or its connections. The flame roll-out switch opens when flame escapes where it should not — and it does not reset itself; per the manual it requires a manual reset, because Carrier wants a human to ask why it opened.
Timing matters too: if the switch stays open longer than three minutes, the board stops calling it 33 and files it as code 13, the lockout version, with a three-hour reset clock.
Homeowner checks — the safe list:
- Air filter first. On limit codes the filter is the cause often enough that a technician will ask about it before anything else.
- Walk the house and open every supply register. Closed or blocked registers strangle airflow.
- Check the returns: rugs, furniture, and storage boxes parked against return grilles count.
- If the code comes back on a clean filter with everything open, the blower or the limit switch itself needs a technician.
Work it in this order
Filter first — pull it, and if you cannot remember when it last changed, that is diagnostic information. Then registers and returns around the house. Then watch one full cycle: a furnace that runs, heats, and trips 33 again on a clean filter with open vents has a blower, switch, or roll-out story, and that is where the homeowner chapter ends. Do not reset a roll-out switch to "see if it happens again" — if it happens again, it already told you twice.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
Questions
Is Carrier code 33 dangerous?
The limit-switch version is the furnace protecting itself from overheating — annoying, not dangerous, and usually airflow. The roll-out version reports flame outside the burner path, which is a genuine hazard. The code alone cannot tell you which switch opened; that is why a repeating 33 gets a technician.
Why did my code change from 33 to 13?
Because three minutes passed with the switch still open. Carrier’s control escalates 33 to lockout code 13 and starts a three-hour auto-reset timer.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.