Error codes · Carrier

Carrier Furnace Code 13 — Limit Circuit Lockout

Code 13 is a hard lockout after the control saw limit openings too many times in one call for heat. Treat it as an airflow emergency first — the same root causes as code 33 — then reset only after the restriction is gone.

Updated July 2026 · 6 min read · United States

Symptoms

Furnace will not stay in heat after several short cycles
LED shows 13 / limit circuit lockout
You may have seen code 33 earlier in the day

Likely causes

Severely dirty filter or closed registers
Oversized/high-MERV filter starving the blower
Weak blower capacitor or failing blower motor
Blocked evaporator coil (AC coil over furnace)

What to do

1. Replace the filter and open registers

Install a clean filter of the exact stamped size. Open supplies and clear returns. High static is the usual path from code 33 into a 13 lockout.

2. Power-cycle to clear the lockout

Switch the furnace off for 60 seconds, then restore power and call for heat once. Do not keep resetting if the limit trips again immediately.

3. Watch the first full cycle

If flame establishes and the blower moves strong air without shutting down, you fixed it. If 33/13 returns, stop DIY resets.

4. Check blower health if airflow still feels weak

A humming blower or delayed spin-up often means a failed run capacitor. Match µF ratings exactly if you replace it.

Stop and call a pro when

Lockout returns after a new filter and open ducts
You suspect a dirty A-coil above the furnace
Any smell of overheating insulation

Carrier Code 33 — What Carrier furnace error code 33 means, how to safely check airflow and the limit switch, and which parts or filters usually clear the fault.
Filter Size Guide — How to read furnace filter dimensions, why nominal vs. actual sizes differ, and which MERV rating to buy without starving airflow.
Goodman 4 Flashes — What Goodman/Amana 4-flash limit codes mean, how to clear airflow restrictions safely, and which filter sizes or blower parts usually stop the trips.
Trane Code 67 — What Trane comfort control code 67 means for heat pumps and AC, when it is normal behavior, and when a control board or sensor is actually failing.
Lennox E229 — What Lennox communicating alert E229 (flame failure) means, safe flame-sensor cleaning steps, and replacement parts that often clear the alert.
Carrier Code 14 — What Carrier furnace error code 14 means, how to safely check flame sensing and ignition, and when to stop and call a licensed tech.

FAQ

Is code 13 worse than code 33?

Code 13 means the board already saw repeated limit events and locked out for safety. Fix airflow before any further resets.

Need a licensed tech instead?

If the guide says to stop — or the part swap did not clear the fault — get free quotes from licensed local HVAC contractors.

Get matched with a pro