Carrier 59SC2B Error Code Code 13: Limit Circuit Lockout

What Does Code Code 13 Mean?

Code 13 on the Carrier 59SC2B is a Limit Circuit Lockout. It means a limit switch or flame rollout switch has been open (triggered) for longer than 3 minutes, causing the control board to shut down the furnace as a safety precaution. The furnace will automatically attempt to reset after three hours.

The limit switch is a temperature-activated safety device. When airflow through the furnace is insufficient, the heat exchanger overheats and the limit switch opens to prevent damage. The most common reason for restricted airflow is a dirty or clogged air filter. Blocked return air vents — from furniture, rugs, or closed dampers — are another frequent cause.

This code is the escalated version of Code 33 (Limit Circuit Fault). If a limit or rollout switch stays open for more than 3 minutes during a Code 33 event, the control board escalates to Code 13 lockout. If the issue is a flame rollout switch, note that it requires manual reset — it will not auto-reset like the limit switch. A flame rollout condition can indicate a serious issue such as a cracked heat exchanger or blocked flue, and should be evaluated by a technician.

If limit or rollout switch opens longer than 3 minutes during operation. The system will escalate to error code 33 .

Common Causes

How to Fix It: Check Air Filter and Return Vents

What You'll Need

• Replacement air filter (if needed)
• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Locate the circuit breaker for your furnace and flip it to OFF. Find the gas shut-off valve on the gas line leading to the furnace and turn it to the closed position. If you smell gas at any point, leave the house immediately and call your gas company from outside.
2. Locate and inspect the air filter The air filter on the Carrier 59SC2B is typically located in the return air duct or at the bottom of the furnace cabinet. Slide the filter out and hold it up to a light. If you cannot see light through it, the filter is clogged and needs to be replaced. Even if it looks only moderately dirty, replace it — a partially clogged filter can still restrict enough airflow to trigger a limit switch.
3. Replace the air filter if dirty Insert a new filter of the same size, making sure the airflow arrow printed on the filter frame points toward the furnace (in the direction of airflow). A standard 1-inch fiberglass or pleated filter is appropriate for this model.
4. Check all return air vents and supply registers Walk through your home and make sure all return air grilles and supply registers are fully open and unobstructed. Move any furniture, curtains, or rugs that may be blocking vents. Ensure no dampers in the ductwork have been accidentally closed.
5. Restore power and wait for the auto-reset Turn the gas supply back on, then turn on the breaker. The Code 13 lockout auto-resets after 3 hours from when it was triggered. If you want to reset it sooner, you can cycle the power off for 30 seconds and then back on. The furnace should attempt a new heating cycle when the thermostat calls for heat.

When to Call a Professional

Contact a licensed HVAC technician if:

• The code returns after replacing the filter and confirming all vents are open
• A flame rollout switch has tripped (it has a manual reset button — this indicates a potentially serious combustion issue)
• The furnace repeatedly cycles between Code 33 and Code 13
• You hear unusual noises from the blower motor area
• You notice a burning smell when the furnace operates