What It Means
Limit or flame rollout switch open or forced high-heat mode from low-heat limit trips.
Carrier Furnace
Carrier Furnace Error Code 33
Troubleshooting guide for the Carrier Furnace system fault 33.
Possible Causes
- Dirty air filter or blocked return/supply vents.
- Blower motor failure or improper speed setting.
- Open primary limit or rollout switch.
- Overheated or damaged heat exchanger.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Limit Circuit Fault. Limit or flame rollout is open, or furnace is operating in high-heat-only mode due to two successive low-heat limit trips.
All Recorded Causes
Check for restricted airflow, dirty filter, or blocked registers. Inspect limit switch and flame rollout switch for continuity. Verify blower motor operation in both heat stages. Check heat exchanger.
Verify Before Replacing Parts
- Confirm the exact Carrier model family and furnaces context before acting on a generic code description.
- Walk the entire heating sequence in order instead of jumping straight to the reported code, watching for check for restricted airflow, dirty filter, or blocked registers.
- Verify each safety device and prove where the sequence stops under live operation, including whether inspect limit switch and flame rollout switch for continuity.
- After the correction, run the system long enough to confirm the furnaces fault does not return under normal load.
Still unsure about this fault?
ACLogics walks you through Carrier Furnace diagnostics step-by-step — so you confirm the cause before swapping parts.
