What causes Carrier Gas Furnace 13?

Excessive return-air restriction: a dirty filter, blocked return-air grilles, or closed dampers. Carrier's guides end the code 13 checklist with this and suggest adding return-air openings if needed. A blower wheel that is loose on the motor shaft, rubs the blower housing, or doesn't turn freely. A blower motor or capacitor that has failed, so the blower doesn't come on within about a minute of the burners lighting. A missing or misaligned limit switch, limit shield, blower baffle, or rear air baffle. A failed limit switch, or an open red wire or bad terminal in the limit circuit. A flame rollout switch that tripped because of inadequate combustion air: reversed vent and combustion-air pipes, poor burner, manifold, or orifice alignment, a blocked heat exchanger, or a heat exchanger leak. A model plug that doesn't match the furnace (variable-speed models), or a failed furnace control board.

How do I fix Carrier Gas Furnace 13?

Confirm the code first: look through the sight glass on the blower door and count 1 short flash then 3 long flashes. Write it down before turning power off. Replace or clean the air filter, and check any second filter location (some homes have a filter at a return grille as well as at the furnace). Make sure return-air grilles aren't blocked by furniture, rugs, or stored items, and that supply registers are open. Clear the lockout by turning the thermostat down (no call for heat) or turning the furnace power switch off for a moment. Carrier's guide notes the control also auto-resets after 3 hours. Set the thermostat to call for heat and watch a full cycle. If the burners light and the blower doesn't start within about a minute, stop and call a pro, since the furnace will overheat. If code 33 starts flashing again soon after, follow our Carrier code 33 page, since lockout 13 is the same limit problem repeated. If the flame rollout switch (a small switch near the burners with a reset button) has tripped, don't keep resetting it. Carrier links repeat rollout trips to combustion-air and heat exchanger problems, so get it inspected.

When should I call a pro for Carrier Gas Furnace 13?

The lockout returns after a filter change with all registers and return grilles open. The blower doesn't start within about a minute of ignition, or the blower wheel is loose, rubbing, or stiff. Carrier's guide checks motor voltage, capacitor, and motor windings here. The flame rollout switch has tripped or trips again after a reset. Carrier's guide calls for checking combustion-air supply, vent and combustion-air pipe routing, burner alignment, and the heat exchangers, which can involve carbon monoxide risk. The limit switch, limit circuit wiring, model plug, or furnace control needs voltage and continuity testing with the furnace powered. External static pressure needs measuring to confirm the duct system isn't too restrictive. You smell gas: leave the house and call your gas utility. Never jumper or bypass the limit or rollout switch.

Code: 13🔥 Carrier Gas Furnace

Carrier Furnace Code 13: Limit Circuit Lockout (Meaning, Causes, Fixes)

Q: What does Carrier Gas Furnace 13 mean?

Status code 13 on a Carrier furnace (1 short flash, then 3 long flashes) is a limit circuit lockout: the high-temperature limit switch or the flame rollout switch stayed open too long or tripped too many times, so the control shut heating down. It usually traces back to the overheating problems behind code 33, with restricted airflow (filters, return grilles, dampers) at the top of Carrier's list. The control auto-resets after 3 hours, but a tripped flame rollout switch must be reset by hand. Carrier status codes are two digits: the first digit is the number of short flashes and the second the number of long flashes, so code 13 is 1 short flash followed by 3 long flashes. On Carrier variable-speed furnaces (troubleshooting guide 58-06T), lockout 13 sets when the limit switch or flame rollout switch is open longer than 3 minutes, or after 10 successive limit trips in high heat; if the switch is open less than 3 minutes, status code 33 keeps flashing instead. On Carrier 2-stage furnaces (guide 58-3T), it sets when the limit switch opened 5 times for at least 3 minutes each during one thermostat cycle. In both cases the furnace control auto-resets after 3 hours. The limit switch resets itself as it cools, but the flame rollout switch (FRS) is manual-reset. Lockout 13 is essentially code 33 (limit circuit fault) that kept happening, so Carrier's guide sends technicians to the code 33 steps for more troubleshooting.

Reviewed 2026-10-23 · Based on 2 manufacturer & service sources

What the code means

Carrier status codes are two digits: the first digit is the number of short flashes and the second the number of long flashes, so code 13 is 1 short flash followed by 3 long flashes. On Carrier variable-speed furnaces (troubleshooting guide 58-06T), lockout 13 sets when the limit switch or flame rollout switch is open longer than 3 minutes, or after 10 successive limit trips in high heat; if the switch is open less than 3 minutes, status code 33 keeps flashing instead. On Carrier 2-stage furnaces (guide 58-3T), it sets when the limit switch opened 5 times for at least 3 minutes each during one thermostat cycle. In both cases the furnace control auto-resets after 3 hours. The limit switch resets itself as it cools, but the flame rollout switch (FRS) is manual-reset. Lockout 13 is essentially code 33 (limit circuit fault) that kept happening, so Carrier's guide sends technicians to the code 33 steps for more troubleshooting.

Likely causes

Excessive return-air restriction: a dirty filter, blocked return-air grilles, or closed dampers. Carrier's guides end the code 13 checklist with this and suggest adding return-air openings if needed
A blower wheel that is loose on the motor shaft, rubs the blower housing, or doesn't turn freely
A blower motor or capacitor that has failed, so the blower doesn't come on within about a minute of the burners lighting
A missing or misaligned limit switch, limit shield, blower baffle, or rear air baffle
A failed limit switch, or an open red wire or bad terminal in the limit circuit
A flame rollout switch that tripped because of inadequate combustion air: reversed vent and combustion-air pipes, poor burner, manifold, or orifice alignment, a blocked heat exchanger, or a heat exchanger leak
A model plug that doesn't match the furnace (variable-speed models), or a failed furnace control board

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Confirm the code first: look through the sight glass on the blower door and count 1 short flash then 3 long flashes. Write it down before turning power off.
Replace or clean the air filter, and check any second filter location (some homes have a filter at a return grille as well as at the furnace).
Make sure return-air grilles aren't blocked by furniture, rugs, or stored items, and that supply registers are open.
Clear the lockout by turning the thermostat down (no call for heat) or turning the furnace power switch off for a moment. Carrier's guide notes the control also auto-resets after 3 hours.
Set the thermostat to call for heat and watch a full cycle. If the burners light and the blower doesn't start within about a minute, stop and call a pro, since the furnace will overheat.
If code 33 starts flashing again soon after, follow our Carrier code 33 page, since lockout 13 is the same limit problem repeated.
If the flame rollout switch (a small switch near the burners with a reset button) has tripped, don't keep resetting it. Carrier links repeat rollout trips to combustion-air and heat exchanger problems, so get it inspected.

🛠 When to call a pro

The lockout returns after a filter change with all registers and return grilles open.
The blower doesn't start within about a minute of ignition, or the blower wheel is loose, rubbing, or stiff. Carrier's guide checks motor voltage, capacitor, and motor windings here.
The flame rollout switch has tripped or trips again after a reset. Carrier's guide calls for checking combustion-air supply, vent and combustion-air pipe routing, burner alignment, and the heat exchangers, which can involve carbon monoxide risk.
The limit switch, limit circuit wiring, model plug, or furnace control needs voltage and continuity testing with the furnace powered.
External static pressure needs measuring to confirm the duct system isn't too restrictive.
You smell gas: leave the house and call your gas utility. Never jumper or bypass the limit or rollout switch.

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

Carrier Furnace Code 13: Limit Circuit Lockout (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Related codes

Sources