Carrier · Furnace / HVAC
33 High limit switch open
What this code means
The furnace's internal temperature exceeded its safe operating limit and the safety switch cut the burners.
Most likely causes
- Clogged air filter restricting airflow
- Blocked supply or return vents
- Failing blower motor not moving enough air
What to try first
Replace the air filter and open any closed vents throughout the house, then reset the system at the thermostat.
Good news: this one is often fixable without a service call. If it persists after the steps above, have it looked at.
Find the part on Amazon →FAQ
What does Carrier error code 33 mean?
High limit switch open. The furnace's internal temperature exceeded its safe operating limit and the safety switch cut the burners.
Can I fix Carrier code 33 myself?
Often, yes. Replace the air filter and open any closed vents throughout the house, then reset the system at the thermostat.
What causes Carrier code 33?
The most common causes are: clogged air filter restricting airflow; blocked supply or return vents; failing blower motor not moving enough air.
Other Carrier furnace codes
All Carrier furnace error codes →
Other furnace brands: Trane · Lennox · Goodman · Amana · American Standard · Rheem · Bryant · Generic · Nest
This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.