Lennox
Lennox Furnaces Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E200
Furnace will not start; thermostat calling for heat but no inducer or ignitor activity; E200 displayed on Lennox control board or thermostat.
Low Voltage Power Interruption / Control Board Lockout
E201
Furnace intermittently shuts down; thermostat or board shows E201; system may restart after power cycle.
Communication Fault Between Thermostat and Furnace Control
E223
Furnace does not respond to thermostat; E223 displayed on Lennox communicating thermostat; may indicate incorrect equipment configuration.
Equipment Configuration / Identification Error
E228
Thermostat shows E228; furnace may not run or may run only in limited mode; often associated with low-voltage issues.
Low Voltage / Communication Bus Error
E250
Lennox communicating thermostat displays E250; furnace may not operate or may be locked out.
High Voltage Polarity / Grounding Error
E312
Thermostat shows E312; furnace may run but with limited control or may not respond to thermostat changes.
Outdoor Unit / Furnace Communication Error (for dual-fuel or integrated systems)
E351
Thermostat displays E351; furnace may shut down unexpectedly or fail to start a heating cycle.
High Temperature Limit / Overheat Lockout (communicating report)
E355
Thermostat shows E355; furnace may short-cycle or not complete a heating call.
Flame Sense / Flame Signal Error (communicating report)
E411
Thermostat displays E411; furnace may not ignite or may shut down shortly after starting.
Ignition Failure / Ignitor Fault (communicating report)
E421
Thermostat shows E421; furnace may start inducer but fail to light burners.
Pressure Switch / Inducer Draft Fault (communicating report)
E431
Thermostat displays E431; furnace may run blower only or shut down after ignition attempt.
Gas Valve / Gas Flow Fault (communicating report)
E434
Thermostat shows E434; furnace may lock out after several failed ignition attempts.
Repeated Ignition Failure Lockout
E438
Thermostat displays E438; furnace may not respond to thermostat commands or may operate erratically.
Internal Control Board Fault (Communicating System)
E439
Thermostat shows E439; furnace may not start or may shut down mid-cycle.
Blower Motor Communication / ECM Fault (Communicating System)
E440
Thermostat displays E440; furnace may not run blower or may run at incorrect speeds.
Blower Motor Speed / Configuration Error
E441
Thermostat shows E441; furnace may run but with poor comfort control or staging issues.
Staging / Capacity Control Error
E444
Thermostat displays E444; furnace may not respond to dehumidification or ventilation commands.
Accessory Control Error (Dehumidifier / Ventilation)
E450
Thermostat shows E450; furnace may not operate in certain modes or may lock out.
Zoning System Communication / Configuration Error
LED_1_FLASH
Status LED on Lennox furnace control board flashes 1 time repeatedly; furnace will not start heating cycle.
Ignition Failure / No Ignition
LED_2_FLASH
Status LED on Lennox furnace control board flashes 2 times repeatedly; inducer may run but burners do not light.
Pressure Switch Stuck Open
LED_3_FLASH
Status LED on Lennox furnace control board flashes 3 times; furnace may start then shut down quickly.
Pressure Switch Stuck Closed
LED_4_FLASH
Status LED on Lennox furnace control board flashes 4 times; furnace may ignite then shut off after a few seconds.
Limit Switch Open / Overheat
LED_5_FLASH
Status LED on Lennox furnace control board flashes 5 times; furnace may not start or may shut down unexpectedly.
Flame Sensed with Gas Valve Off
LED_6_FLASH
Status LED on Lennox furnace control board flashes 6 times; furnace may not respond to thermostat.
Line Voltage Polarity / Ground Fault
LED_7_FLASH
Status LED on Lennox furnace control board flashes 7 times; furnace may lock out after several failed ignition attempts.
Lockout Due to Repeated Ignition Failures
LED_STEADY_OFF
Lennox furnace control board LED is completely off; furnace is non-responsive.
No Power to Control Board
Symptom
Furnace blower runs continuously even when thermostat is not calling for heat or fan.
Blower Stuck On / Fan Relay Stuck Closed
Symptom
Furnace cycles on and off frequently, causing temperature swings and high energy use.
Short Cycling Due to Control or Sizing Issues
Symptom
Furnace frequently trips the household circuit breaker.
Electrical Overload / Short Circuit
Symptom
Furnace inducer motor runs but burners never light; you hear clicking or see ignitor glow but no flame.
No Gas Flow to Burners
Symptom
Furnace is very loud at the return grille; whistling or roaring sound when running.
Restricted Return Air / High Static Pressure
Symptom
Furnace makes loud banging or booming noise at startup when burners ignite.
Delayed Ignition / Burner Flashback
Symptom
Furnace occasionally shuts down and restarts after windy conditions; vent terminations are on the windward side of the house.
Wind-Induced Pressure Switch Trips
Symptom
Furnace produces a high-pitched whine or screeching noise during operation.
Blower or Inducer Motor Bearing Failure
Symptom
Furnace runs but produces no heat; blower runs continuously with cool air from vents.
Burners Not Igniting / No Flame
Symptom
Furnace runs but some rooms are cold while others are warm.
Airflow Imbalance / Duct Issues
Symptom
Furnace short cycles; burners light for a few seconds to a minute, then shut off, repeating frequently.
High Limit Cycling / Overheating
Symptom
Furnace starts but shuts down after 30–60 seconds with no obvious error code at thermostat.
Flame Loss During Run
Symptom
Furnace vibrates excessively and causes rattling noises in ductwork.
Blower Imbalance / Mounting Issues
Symptom
Furnace will not start at all; no blower, no inducer, no LED lights, but other appliances have power.
Complete Power Loss to Furnace
Symptom
Strong burning or electrical smell when furnace runs.
Overheating Components / Electrical Fault
Symptom
Thermostat calls for heat but furnace only runs the inducer; blower never comes on and furnace overheats.
Blower Motor Not Starting
Symptom
Water leaking from around the base of a high-efficiency Lennox furnace.
Condensate Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E200 |
Furnace will not start; thermostat calling for heat but no inducer or ignitor activity; E200 displayed on Lennox control board or thermostat.
|
Low Voltage Power Interruption / Control Board Lockout | View Details |
| E201 |
Furnace intermittently shuts down; thermostat or board shows E201; system may restart after power cycle.
|
Communication Fault Between Thermostat and Furnace Control | View Details |
| E223 |
Furnace does not respond to thermostat; E223 displayed on Lennox communicating thermostat; may indicate incorrect equipment configuration.
|
Equipment Configuration / Identification Error | View Details |
| E228 |
Thermostat shows E228; furnace may not run or may run only in limited mode; often associated with low-voltage issues.
|
Low Voltage / Communication Bus Error | View Details |
| E250 |
Lennox communicating thermostat displays E250; furnace may not operate or may be locked out.
|
High Voltage Polarity / Grounding Error | View Details |
| E312 |
Thermostat shows E312; furnace may run but with limited control or may not respond to thermostat changes.
|
Outdoor Unit / Furnace Communication Error (for dual-fuel or integrated systems) | View Details |
| E351 |
Thermostat displays E351; furnace may shut down unexpectedly or fail to start a heating cycle.
|
High Temperature Limit / Overheat Lockout (communicating report) | View Details |
| E355 |
Thermostat shows E355; furnace may short-cycle or not complete a heating call.
|
Flame Sense / Flame Signal Error (communicating report) | View Details |
| E411 |
Thermostat displays E411; furnace may not ignite or may shut down shortly after starting.
|
Ignition Failure / Ignitor Fault (communicating report) | View Details |
| E421 |
Thermostat shows E421; furnace may start inducer but fail to light burners.
|
Pressure Switch / Inducer Draft Fault (communicating report) | View Details |
| E431 |
Thermostat displays E431; furnace may run blower only or shut down after ignition attempt.
|
Gas Valve / Gas Flow Fault (communicating report) | View Details |
| E434 |
Thermostat shows E434; furnace may lock out after several failed ignition attempts.
|
Repeated Ignition Failure Lockout | View Details |
| E438 |
Thermostat displays E438; furnace may not respond to thermostat commands or may operate erratically.
|
Internal Control Board Fault (Communicating System) | View Details |
| E439 |
Thermostat shows E439; furnace may not start or may shut down mid-cycle.
|
Blower Motor Communication / ECM Fault (Communicating System) | View Details |
| E440 |
Thermostat displays E440; furnace may not run blower or may run at incorrect speeds.
|
Blower Motor Speed / Configuration Error | View Details |
| E441 |
Thermostat shows E441; furnace may run but with poor comfort control or staging issues.
|
Staging / Capacity Control Error | View Details |
| E444 |
Thermostat displays E444; furnace may not respond to dehumidification or ventilation commands.
|
Accessory Control Error (Dehumidifier / Ventilation) | View Details |
| E450 |
Thermostat shows E450; furnace may not operate in certain modes or may lock out.
|
Zoning System Communication / Configuration Error | View Details |
| LED_1_FLASH |
Status LED on Lennox furnace control board flashes 1 time repeatedly; furnace will not start heating cycle.
|
Ignition Failure / No Ignition | View Details |
| LED_2_FLASH |
Status LED on Lennox furnace control board flashes 2 times repeatedly; inducer may run but burners do not light.
|
Pressure Switch Stuck Open | View Details |
| LED_3_FLASH |
Status LED on Lennox furnace control board flashes 3 times; furnace may start then shut down quickly.
|
Pressure Switch Stuck Closed | View Details |
| LED_4_FLASH |
Status LED on Lennox furnace control board flashes 4 times; furnace may ignite then shut off after a few seconds.
|
Limit Switch Open / Overheat | View Details |
| LED_5_FLASH |
Status LED on Lennox furnace control board flashes 5 times; furnace may not start or may shut down unexpectedly.
|
Flame Sensed with Gas Valve Off | View Details |
| LED_6_FLASH |
Status LED on Lennox furnace control board flashes 6 times; furnace may not respond to thermostat.
|
Line Voltage Polarity / Ground Fault | View Details |
| LED_7_FLASH |
Status LED on Lennox furnace control board flashes 7 times; furnace may lock out after several failed ignition attempts.
|
Lockout Due to Repeated Ignition Failures | View Details |
| LED_STEADY_OFF |
Lennox furnace control board LED is completely off; furnace is non-responsive.
|
No Power to Control Board | View Details |
| – |
Furnace blower runs continuously even when thermostat is not calling for heat or fan.
|
Blower Stuck On / Fan Relay Stuck Closed | View Details |
| – |
Furnace cycles on and off frequently, causing temperature swings and high energy use.
|
Short Cycling Due to Control or Sizing Issues | View Details |
| – |
Furnace frequently trips the household circuit breaker.
|
Electrical Overload / Short Circuit | View Details |
| – |
Furnace inducer motor runs but burners never light; you hear clicking or see ignitor glow but no flame.
|
No Gas Flow to Burners | View Details |
| – |
Furnace is very loud at the return grille; whistling or roaring sound when running.
|
Restricted Return Air / High Static Pressure | View Details |
| – |
Furnace makes loud banging or booming noise at startup when burners ignite.
|
Delayed Ignition / Burner Flashback | View Details |
| – |
Furnace occasionally shuts down and restarts after windy conditions; vent terminations are on the windward side of the house.
|
Wind-Induced Pressure Switch Trips | View Details |
| – |
Furnace produces a high-pitched whine or screeching noise during operation.
|
Blower or Inducer Motor Bearing Failure | View Details |
| – |
Furnace runs but produces no heat; blower runs continuously with cool air from vents.
|
Burners Not Igniting / No Flame | View Details |
| – |
Furnace runs but some rooms are cold while others are warm.
|
Airflow Imbalance / Duct Issues | View Details |
| – |
Furnace short cycles; burners light for a few seconds to a minute, then shut off, repeating frequently.
|
High Limit Cycling / Overheating | View Details |
| – |
Furnace starts but shuts down after 30–60 seconds with no obvious error code at thermostat.
|
Flame Loss During Run | View Details |
| – |
Furnace vibrates excessively and causes rattling noises in ductwork.
|
Blower Imbalance / Mounting Issues | View Details |
| – |
Furnace will not start at all; no blower, no inducer, no LED lights, but other appliances have power.
|
Complete Power Loss to Furnace | View Details |
| – |
Strong burning or electrical smell when furnace runs.
|
Overheating Components / Electrical Fault | View Details |
| – |
Thermostat calls for heat but furnace only runs the inducer; blower never comes on and furnace overheats.
|
Blower Motor Not Starting | View Details |
| – |
Water leaking from around the base of a high-efficiency Lennox furnace.
|
Condensate Leak | View Details |
No matching codes found
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