Why Furnaces Lock Out
A furnace lockout is a built-in safety response. The control board detects a fault and stops operation to prevent damage or dangerous conditions. After detecting the same fault multiple times (typically 3 to 5 attempts), the board enters lockout mode. The gas valve stays closed and the furnace will not restart until you manually reset it.
Lockouts fall into two categories. Soft lockout clears automatically after the furnace cools down and you reset the power. Hard lockout requires intentional user action beyond power cycling, such as pressing a reset button or clearing a specific error code on the control board.
The Universal Reset Procedure
Every furnace has a baseline reset method. This works for initial troubleshooting across all brands.
Turn the thermostat to OFF. Go to the breaker panel. Flip the furnace circuit breaker to OFF. Wait 60 seconds. Flip the breaker back to ON. Set the thermostat to HEAT and raise it above room temperature. Watch the furnace for one complete heating cycle.
This universal reset works because the control board loses all memory during the 60-second power-off period. When power returns, the board starts fresh. If the root cause of the lockout is still present, the furnace will re-lockout within one or two cycles.
Carrier and Bryant
Carrier furnaces use two forms of lockout. Code 11 through code 19 error codes typically clear with a power cycle. Code 13 (limit circuit lockout) and code 14 (ignition lockout) may require addressing the root cause before the reset holds.
Reset procedure: Turn the thermostat to OFF. Flip the furnace breaker to OFF. Wait until the control board LED on the furnace extinguishes completely (this may take 30 seconds for the capacitors to drain). Restore power. Set thermostat to HEAT.
Carrier Infinity and Comfort series furnaces with communicating thermostats can also be reset through the thermostat menu: navigate to Installer Setup or Reset and confirm the reset. This sends a clear command to the control board.
Carrier models without a thermostat menu reset: some Carrier control boards have a reset button. Look for a small push button labeled “RESET” on the control board near the 24V terminal strip. Press and hold for 5 seconds.
For Carrier code 13 lockout specifically, the furnace must complete a successful heating cycle without the limit switch tripping. If the limit switch opens during the first cycle after reset, the board returns to lockout immediately. Fix the airflow problem before investing time in multiple resets.
Trane and American Standard
Trane flash code lockouts clear with a standard power cycle. Some Trane models have a reset button on the control board.
Reset procedure: Set the thermostat to OFF. Turn off the furnace disconnect switch or breaker. Wait 30 seconds. Restore power. Wait for the furnace to complete its startup sequence.
Trane control boards with a reset button: look for a small button labeled “STATUS RECALL” or “RESET” on the edge of the control board. Press the button once. The LED will flash the last stored error code. Press and hold the button for 5 seconds to clear the error history. This clears the lockout.
American Standard furnaces use the exact same reset procedure. The control boards are identical. Use the Trane procedure for any American Standard model.
Lennox
Lennox furnaces have the most specific reset procedure. Power cycling alone may not clear a Lennox lockout. The diagnostic button on the control board plays a central role.
Reset procedure: Turn the thermostat to OFF. Flip the breaker to OFF. Wait 30 seconds. Restore power. Set the thermostat to HEAT.
If the furnace does not restart, locate the diagnostic push button on the Lennox control board. Press and hold the diagnostic button for 5 seconds. The LED will flash and the board will clear any soft lockout. Release the button. The furnace should begin its ignition sequence.
For Lennox Elite and Merit series, the diagnostic button also serves as a history recall. Press and release the button to see the last 5 stored fault codes. If you hold the button for 10 seconds, the board clears all stored faults.
Lennox iComfort thermostat owners can also reset through the thermostat. Navigate to Menu, then Installer/System Setup, then Reset. Select Clear Error History. This does not replace the diagnostic button reset for hard lockouts.
For Lennox code 414 (rollout switch open), the diagnostic button reset does not work. The rollout switch has a physical manual reset button on the switch body. Locate the rollout switch on the burner manifold and press the center button until it clicks.
Goodman and Amana
Goodman furnaces use the simplest reset procedure. Power cycling clears most flash codes.
Reset procedure: Turn the thermostat to OFF. Flip the furnace breaker to OFF. Wait 30 seconds. Restore power. Set the thermostat to HEAT. The furnace will restart and attempt ignition.
Goodman control boards do not have a dedicated reset button. All code clearing happens through power cycling. If the furnace fails to start after a power cycle, the root cause is still present and must be diagnosed.
Goodman 2-digit code E1 (internal control board fault), E2 (watchdog timeout), and E3 (limit circuit open) all clear with a power cycle but will return if the underlying fault remains. Code EF (flame with no call for heat) is a safety-critical code that may require flame sensor cleaning in addition to power cycling. Remove and clean the flame sensor with emery cloth, then power cycle.
Amana furnaces use identical control boards. Follow the Goodman procedure.
Rheem and Ruud
Rheem furnaces require a specific sequence for a clean reset. Turning the breaker off and back on is not always enough.
Reset procedure: First, turn the thermostat to OFF. Wait 10 seconds. Then flip the furnace breaker to OFF. Wait 60 seconds. Restore power. Set the thermostat to HEAT.
Rheem Prestige and Endeavor series with numeric code display: after power cycling, the display should show “11” (no previous code). If it shows the previous code (such as 13 or 14), the board has not cleared. Turn the breaker off for 5 minutes to fully drain the holding capacitors.
Some Rheem control boards have a reset jumper on the board labeled J2 or J3. Moving this jumper can clear stored codes. Consult your model’s wiring diagram before moving jumpers.
Ruud furnaces use the exact same reset procedure as Rheem. The control boards are interchangeable.
York
York furnace lockouts typically clear with a standard power cycle. Some York models require changing dip switch settings to restore operation after certain lockouts.
Reset procedure: Turn the thermostat to OFF. Flip the breaker to OFF. Wait 30 seconds. Restore power. Set thermostat to HEAT.
York control boards with a red LED: the LED will flash slowly during normal operation. If the LED shows a rapid flash or steady on, the board is in lockout. Power cycling clears this.
Some York models use a control board with a TEST pin. Shorting the TEST pin to ground during the startup cycle enters diagnostic mode. Do not use this unless you have the specific York wiring diagram for your model.
Soft Lockout vs Hard Lockout
Soft lockout happens when the board detects a fault and stops the furnace. Power cycling clears it. The furnace will attempt one heat cycle. If the fault persists, the board returns to lockout.
Hard lockout happens after repeated faults (typically 3 to 5 ignition attempts or 3 limit switch trips). Hard lockout requires clearing stored error history on the control board. On Carrier and Lennox, this may require a specific diagnostic button sequence. On Goodman and Rheem, a 5-minute power-off period clears the hard lockout.
If a furnace re-enters lockout immediately after reset (within 5 minutes), the fault is active and needs diagnosis. Multiple resets without diagnosis risk damaging the furnace and create a carbon monoxide hazard. The furnace safety system is working. Listen to it.
Warnings
Do not reset a furnace more than 3 times without diagnosing the root cause. Repeated resetting can damage the heat exchanger, ignitor, and gas valve. If the furnace trips the same code within one heating cycle after reset, the problem needs professional attention.
If the furnace is in a 90%+ high-efficiency model, check the condensate drain before resetting. Blocked condensate drains cause pressure switch lockouts that look like ignition failures. Clearing the drain often resolves the lockout without needing to reset anything.
Do not bypass safety switches to force the furnace to run. Bypassing the limit switch, rollout switch, or pressure switch removes the protection that prevents fire and explosion.
When to Call a Professional
Call a technician if the furnace locks out again within one heat cycle after you follow the correct brand-specific reset procedure. Repeated lockout means the component causing the fault has not been identified.
Specific situations that require a professional:
- The furnace leaks water on the floor (frozen condensate drain, cracked heat exchanger)
- You smell gas at any point during the reset process
- The furnace produces a burning smell after restarting
- You hear banging or popping sounds from the burner area during ignition
- The rollout switch trips when you reset and the furnace fires