Carrier 58MVP Error Code Code 13: Limit Switch Lockout

What Does Code Code 13 Mean?

The limit switch is a safety device that shuts off the burners when the heat exchanger gets dangerously hot. Code 13 means the limit switch has tripped too many times in succession: 10 trips during high-heat operation, or just 3 trips during low-heat operation. The control locks out the furnace to prevent potential damage.

On the 58MVP, there is an important escalation behavior: after 2 low-fire limit trips, the control locks the furnace into high-heat-only mode. On boards with date codes of 9906 or later, this lockout into high-heat mode is permanent (cannot be forced back into low-heat) until the underlying issue is fixed. If a third low-fire limit trip occurs (on older boards), or if 10 high-heat limit trips occur, code 13 lockout is triggered.

The most common cause is restricted airflow — usually a dirty air filter or blocked registers. When the blower cannot move enough air across the heat exchanger, temperatures rise until the limit switch opens. Other causes include a misaligned limit switch or limit shield, improper gas input adjustment, or a blower motor issue.

Common Causes

How to Fix It: Check Air Filter and Registers

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 (typically at the bottom of the furnace or in the return air duct). Remove it and inspect. If it is visibly dirty or clogged, replace it with a new filter of the same size. A restricted filter is the most common cause of repeated limit switch trips.
3. Open all supply and return registers throughout the house Walk through every room and confirm all supply registers and return air grilles are fully open and unblocked. Move furniture, rugs, or other items away from vents. Even partially closed registers reduce airflow enough to cause overheating in some configurations.
4. Restore power and gas, then wait for auto-reset Turn the gas supply valve back to the open position (parallel to the pipe). Turn the breaker back ON. The furnace will auto-reset after 3 hours. After the reset, set your thermostat to call for heat and monitor the furnace through several heating cycles.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 13 returns after replacing the filter and opening all registers
• The furnace is stuck in high-heat-only mode and won't return to two-stage operation
• You suspect the limit switch or limit shield is misaligned or damaged
• The blower motor sounds abnormal or does not seem to be running at proper speed
• There is an overheating smell or visible discoloration near the heat exchanger area
• The furnace locks out frequently (more than once per heating season)