Carrier 59SC5A Error Code 13: Limit Circuit Lockout

What Does Code 13 Mean?

Code 13 on the Carrier 59SC5A is a Limit Circuit Lockout. A limit switch or flame rollout switch has been open (triggered) for longer than 3 minutes, and the control board has locked out the furnace as a safety measure. The system will automatically attempt to reset after three hours.

The limit switch monitors heat exchanger temperature. When airflow across the heat exchanger is insufficient, temperatures rise beyond safe levels and the switch opens to prevent damage. The most common cause is simply a dirty or clogged air filter that restricts airflow. Blocked return air vents or supply registers — from furniture, closed dampers, or other obstructions — are another frequent culprit.

Code 13 is the escalated version of Code 33 (Limit Circuit Fault). When a limit or rollout switch stays open for more than 3 minutes during a Code 33 event, the board escalates to this lockout. If the flame rollout switch is the one that tripped, it requires manual reset — there is a small button on the switch body. A flame rollout condition may indicate a more serious combustion problem and warrants professional evaluation.

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 59SC5A is typically found in the return air duct or at the bottom of the furnace cabinet. Slide the filter out and hold it up to a light source. If light does not pass through easily, the filter is clogged and must be replaced.
3. Replace the air filter if dirty Insert a new filter of the same size. Make sure the airflow direction arrow on the filter frame points toward the furnace (in the direction of airflow). Use a standard 1-inch fiberglass or pleated filter appropriate for your filter slot size.
4. Check all return air vents and supply registers Walk through your entire home and confirm all return air grilles and supply registers are fully open and not blocked by furniture, curtains, or rugs. Check that no duct dampers have been accidentally closed.
5. Restore power and wait for the reset Turn the gas supply back on, then turn on the breaker. The Code 13 lockout auto-resets after 3 hours, but you can reset it sooner by cycling the power off for 30 seconds and back on. When the thermostat calls for heat, the furnace should attempt a new heating cycle.

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 (identified by its manual reset button) — this may indicate a cracked heat exchanger or blocked flue
• The furnace repeatedly cycles between Code 33 and Code 13
• You hear unusual noises from the blower motor
• You smell burning when the furnace runs