Code 33 (Furnace) — Limit Fault

What does 33 mean?

This fault on a furnace indicates that a safety limit switch has tripped, usually due to excessive temperature within the unit. This causes the furnace to shut down to prevent damage.

• Restricted airflow from dirty filters or closed vents
• Malfunctioning blower motor
• Failed limit switch
• Combustion issues causing excessive heat

Click steps to track your progress.

1. 1

   Check and replace dirty air filters to ensure good airflow.

2. 2

   Verify that all supply and return air vents are fully open and unobstructed.

3. 3

   Turn off the furnace at the circuit breaker for 30 seconds to reset the system.

4. 4

   If the limit fault continues, contact a qualified HVAC technician for further investigation.