Carrier 58MVC Error Code Status Code 33: Limit Circuit Fault

What Does Code Status Code 33 Mean?

Code 33 indicates that the high-temperature limit switch or flame rollout switch has opened, meaning the furnace detected an unsafe temperature condition and cut off gas flow to the burners as a safety measure. The blower will continue running for 4 minutes at medium-heat airflow (or until the switch closes again, whichever takes longer) to cool the heat exchanger down.

If the switch remains open for more than 3 minutes, the code escalates to code 13 (limit circuit lockout). If it closes within 3 minutes, code 33 continues flashing until the blower shuts off, and the furnace attempts to resume normal operation. However, if 2 successive low- or medium-heat limit trips occur, the furnace will switch to high-heat-only mode as a protective measure.

The most common cause is restricted airflow from a dirty air filter or blocked vents, which prevents the blower from removing heat fast enough. Other causes include reversed vent and combustion-air pipes, a loose blower wheel, or a defective limit switch. Note that the flame rollout switch requires a manual reset (it has a red button) — if it has tripped, this indicates a serious combustion issue and you should have a professional inspect before resetting it.

If limit or flame rollout switch remains open longer than 3 minutes. The system will escalate to error code 13 .

Common Causes

How to Fix It: Check Air Filter and Vents

What You'll Need

• Replacement air filter (if needed)
• Flashlight

Steps

1. Turn off power at the breaker or power switch AND shut off the gas supply Locate the furnace circuit breaker and turn it OFF. Find the gas shutoff valve on the supply line to the furnace and turn it to the closed position (perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
2. Check and replace the air filter Locate the air filter at the bottom of the furnace or in the return air duct. Remove it and inspect — if it is visibly dirty, clogged, or you cannot see light through it, replace it with a new filter of the same size. This is the most common fix for code 33.
3. Check all supply and return vents in the house Walk through every room and make sure all supply registers and return air grilles are fully open and unobstructed. Move any furniture, rugs, boxes, or curtains that may be blocking airflow. Closing too many vents can cause the same overheating issue as a dirty filter.
4. Restore power and gas, then test Turn the gas supply valve back to the open position (parallel to the pipe). Turn the breaker back ON. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 33 returns after replacing the filter and opening all vents
• The flame rollout switch has tripped (red button popped out) — do not reset it yourself without professional inspection, as this indicates a combustion safety issue
• The furnace has switched to high-heat-only mode and won't return to normal multi-stage operation
• The blower sounds weak, makes unusual noises, or does not seem to be moving enough air
• You notice an overheating smell coming from the furnace
• Code 33 escalates to code 13 (lockout) repeatedly