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Lennox Furnace Error Codes
258 error codes for Lennox furnace models. Each links to the full diagnostic procedure from the service manual.
CodeDescription
1Reverse line voltage polarity.1 FlashFlame present with gas valve de-energized (control 103085).1+2Low flame current during run mode (Board 100869).1+3Flame sensed out of sequence10Watchguard11Pressure switch stuck closed prior to activation of combustion air inducer.12Flame Sensed without gas valve energized.13Low Line Voltage.2Improper Earth Ground.2 FlashesPressure switch closed with combustion air inducer de-energized (control…2 Flashes (RAM)Control lockout2+3Low fire pressure switch sensed open; 80%2+4Low fire pressure switch sensed closed prior to activation of combustion air…2+5High fire pressure switch sensed open. 80%2+6High fire pressure switch sensed closed prior to activation of combustion air…2+7Low pressure switch opened during ignition trial or heating demand (Board…3Burner failed to light, or lost flame during heat demand.3 FlashesPressure switch open with combustion air inducer energized (Control 103085).3 Flashes (RAM)Pressure switch open3+1Limit switch open (primary or secondary).MyPros+ Max
Get the full diagnostic procedure for any Lennox furnace error code.
- Step-by-step tests with expected resistance, voltage, and continuity values
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4Low Flame Signal4 FlashesPrimary limit switch open (Control 103085).4 Flashes (RAM)Open limit4+1Watchguard4+2Watchguard4+3Watchguard4+5Watchguard4+6Watchguard4+7Watchguard4+8Low line voltage (below 90 volts for board 100870).5Watchguard5 FlashesRollout switch open (control 103085).5 Flashes (RAM)Flame sensed and gas valve not energized.5+1Hard lockout5+2Control failed self check, internal error; control will restart if error…5+3No Earth ground; control will restart if error recovers (Board 100869).5+4Reversed line voltage polarity; control will restart if the error recovers…5+5Low 24V (control will restart if voltage rises to normal).5+6Low secondary (24VAC) voltage (Board 100869).6 FlashesPressure switch cycle lockout (control 103085).7Primary or Secondary Limit Open or Watchguard Mode7 FLASHESLockout8Rollout switch open.8 FlashesLockout9Pressure Switch failed to close or opened during heat demand.9 FlashesLine voltage polarity incorrect (Control 103085).DIAG#1: Alternate Flash / DIAG#2: Alternate FlashWatchguardDIAG#1: Continuous On / DIAG#2: Continuous OnCircuit board self-check failure or ignition/blower control is wired…DIAG#1: Flash / DIAG#2: OffPressure switch WatchguardDIAG#1: Off / DIAG#2: FlashFlame sensed without gas valve energized.DIAG#1: On / DIAG#2: FlashPrimary or secondary limit switch open (auto-reset switch).DIAG#1: Simultaneous Flash / DIAG#2: Simultaneous FlashPower ON, normal operation; increased flash rate indicates a heating demand.DS1 Alternating Fast Flash / DS2 Alternating Fast FlashDuring ignitor warm-up period onlyDS1 Alternating Slow Flash / DS2 Alternating Slow FlashWatchguardDS1 Fast Flash / DS2 Fast FlashNormal operationDS1 Fast Flash / DS2 Fast Flash (simultaneous)Normal operationDS1 Fast Flash / DS2 Slow FlashDuring ignitor warm-up period onlyDS1 OFF / DS2 Fast FlashHigh pressure switch open, or blocked inlet/exhaust vent, or high pressure…DS1 Off / DS2 OnLow flame signal; measures below 0.23 microAmpsDS1 OFF / DS2 Slow FlashLow pressure switch open, or blocked inlet/exhaust vent, or low pressure switch…DS1 On / DS2 OffMain power polarity reversed; switch line and neutral.DS1 On / DS2 OnCircuit board failure or control wired incorrectly; check 24 and 115 volts to…DS1 Slow Flash / DS2 Fast FlashLow flame signalDS1 Slow Flash / DS2 OffFlame sensed without gas valve energized.DS1 Slow Flash / DS2 ONPrimary, secondary, backup secondary or rollout limit switch open; limits must…DS1 Slow Flash / DS2 Slow FlashPower onDS1 Slow Flash / DS2 Slow Flash (simultaneous)Power onDS1: OFF / DS2: Fast FlashHigh pressure switch open; OR blocked inlet/exhaust vent; OR high pressure…DS1: OFF / DS2: Slow FlashLow-fire pressure switch open (G32Q-75 only); or blocked inlet/exhaust vent; or…DS1: Slow Flash / DS2: ONPrimary, secondary or rollout limit switch open; limits must close within 3…DS1/DS2 Alternating Fast FlashDuring ignitor warm-up onlyDS1/DS2 Alternating Slow FlashWatchguardE 110Low line voltage detected (voltage lower than nameplate rating).E 113High line voltage detected (voltage higher than nameplate rating).E 114Line voltage frequency out-of-range (no 60 Hertz power).E 125Control failed self-check, internal error, failed hardware (flame sense circuit…E 207Hot surface ignitor sensed open.E 226High pressure switch failed closed.E 227Low pressure switch open during trial for ignition or run mode.E 240Low flame current during run mode.E 241Flame sensed out of sequenceE 250Limit switch circuit open.E 271Soft lockoutE 272Soft lockoutE 273Soft lockoutE 274Soft lockoutE 290Ignitor circuit faultE105Device communication problemE111Line voltage polarity reversed.E112Ground not detected; system shuts down.E115Low 24V power (range is 18 to 30 volts); control will restart if the error…E116High 24V (range is 18 to 30 volts).E117Poor ground detected (warning only).E120Unresponsive device (communication only), usually caused by delay in outdoor…E124Active communicating thermostat signal missing for more than 3 minutes.E126Control internal communication problem.E131Corrupted control parameters (communicating only).E180Outdoor air temperature sensor failure (shorted or out-of-range).E200Device communication problemE201Indoor blower communication failureE202Indoor blower motor mis-matchE203Appliance capacity/size is NOT programmed; invalid unit codes.E204Line voltage frequency out-of-range; no 60 hertz power.E205Low 24VE206Indoor blower motor mis-matchE208Gas valve mis-wired.E209Gas valve control relay contact shorted.E210Unresponsive device; usually caused by delay in outdoor unit responding to…E211Active communicating thermostat signal missing for more than 3 minutes; lost…E212Control failed self-check, internal error, failed hardware; covers hardware…E213Failed internal control communication between microcontrollers.E214Corrupted control parameters (verify configuration of system).E215Outdoor air sensor failureE218Indoor blower communication failureE220Hard lockoutE221Low pressure switch failed open.E222Low pressure switch failed closed.E223High pressure switch failed open.E224Low pressure switch failed closed (stuck closed on heat call longer than 150…E225Low pressure switch open during trial for ignition or run mode.E228Unable to perform successful pressure switch calibration.E229Ignition on High FireE251Discharge air temperature too high (gas heat only).E252Discharge air temperature too high (gas heat only).E260Soft lockoutE261Soft lockoutE262Soft lockoutE263Soft lockoutE264Soft lockoutE265Soft lockoutE266Soft lockoutE269Ignitor circuit faultE270Restricted air flowE275Heat rate reduced to match indoor blower air flow; furnace blower in cutback…E276Restricted air flow in cooling or continuous fan mode is lower than cfm…E277Indoor or outdoor unit capacity mismatch.E278Global network connectionE280No 24 Volt output on Y1 to C with non-communicating outdoor unit; Y1…E281No 24 Volt output on Y2 to C with non-communicating outdoor unit; Y2…E282No 24 Volts between R & O with non-communicating outdoor unit (dual fuel module…E291Heat air flow restricted below the minimum.E292Indoor blower motor unable to start due to obstructed wheel or seized bearings.E294Combustion air inducer over current.E295Indoor blower motor temperature is too high (motor tripped on internal…E300LSOME301LSOME302LSOME303LSOME304LSOME305LSOME306LSOME307LSOME308LSOME310Discharge air temperature sensor failure (shorted or out of range).E311Heat rate reduced to match indoor blower air flow (furnace blower in cutback…E312Restricted air flow in cooling or continuous fan mode is lower than cfm setting…E313Indoor or outdoor unit capacity mismatch (communication only).E331Global network connectionE334Relay Y1 stuck on integrated control.E347No 24 Volt output on Y1 of integrated control with non-communicating outdoor…E348No 24 Volt output on Y2 of integrated control with non-communicating outdoor…E349No 24 Volts between R & O on integrated control with non-communicating outdoor…E370Interlock switch sensed open for 2 minutes.E400LSOME401LSOME402LSOME403LSOME404LSOME405LSOME406LSOME407LSOME408LSOME409LSOMFast Flash (RAM)Normal operation with call for heat (RAM control).HeartbeatNormal operationLED Flashing 1/2 sec on 1/2 sec offLockout or Restricted Lockout condition on the R7184B burner control.LED Flashing 2 sec on 2 sec offBurner control is in Recycle modeLED OnFlame sensed by the R7184B burner control (cad cell detecting light).LED Slow FlashControl retry periodLED Steady OnNormal operation of the G776 ignition control (-1 through -4 models).LED-OFFControl failure or power failure or hard lockout (G776 ignition control, -1 and…LED-SLOW_FLASH_1ON_5OFFControl retry periodLED-STEADY_ONNormal operation (G776 ignition control, -1 and -2 models).LED#1 Alternating Fast Flash / LED#2 Alternating Fast FlashSensed during ignitor warm-up period onlyLED#1 Alternating Slow Flash / LED#2 Alternating Slow FlashWatchguardLED#1 Fast Flash / LED#2 Fast Flash (simultaneous)Normal operation, signaled when heating demand initiated at thermostat.LED#1 Fast Flash / LED#2 Slow FlashMain power polarity reversedLED#1 OFF / LED#2 ONCircuit board failure or control wired incorrectly.LED#1 Off / LED#2 Slow FlashPressure switch open or has opened 5 times during a single call for heat; OR…LED#1 ON / LED#2 OFFCircuit board failure or control wired incorrectly.LED#1 ON / LED#2 ONCircuit board failure or control wired incorrectly.LED#1 ON / LED#2 Slow FlashRollout switch open, or 12-pin connector improperly attached.LED#1 Simultaneous Fast Flash / LED#2 Simultaneous Fast FlashNormal operationLED#1 Simultaneous Slow Flash / LED#2 Simultaneous Slow FlashPower on, normal operation; also signaled during cooling and continuous fan.LED#1 Slow Flash / LED#2 Fast FlashLow flame signalLED#1 Slow Flash / LED#2 OFFFlame sensed without gas valve energized.LED#1 Slow Flash / LED#2 ONPrimary or secondary limit open; limit must close within specified trials/time…LED#1 Slow Flash / LED#2 Slow Flash (simultaneous)Power on, normal operation; also signaled during cooling and continuous fan.LED#1: Alternating Fast Flash / LED#2: Alternating Fast FlashImproper main ground or line voltage below 75 volts; or broken ignitor; or open…LED#1: Alternating Slow Flash / LED#2: Alternating Slow FlashWatchguardLED#1: Fast Flash / LED#2: Slow FlashMain power polarity reversedLED#1: Off / LED#2: OnCircuit board failure or control wired incorrectly.LED#1: Off / LED#2: Slow FlashPressure switch open or has opened 5 times during a single call for heat; or…LED#1: On / LED#2: OffCircuit board failure or control wired incorrectly.LED#1: On / LED#2: OnCircuit board failure or control wired incorrectly.LED#1: On / LED#2: Slow FlashRollout switch open or 9-pin connector improperly attached.LED#1: Slow Flash / LED#2: Fast FlashLow flame signalLED#1: Slow Flash / LED#2: OffFlame sensed without gas valve energized.LED#1: Slow Flash / LED#2: OnPrimary or secondary limit open; limit must close within specified trials/time…LED1 ALT FAST FLASH / LED2 ALT FAST FLASHDuring ignitor warm-upLED1 ALT SLOW FLASH / LED2 ALT SLOW FLASHWatchguardLED1 Alternating Fast Flash / LED2 Alternating Fast FlashImproper main ground (controls 10M93, 57L84 during ignitor warm up only…LED1 ALTERNATING SLOW FLASH / LED2 ALTERNATING SLOW FLASHWatchguardLED1 FAST FLASH / LED2 FAST FLASHNormal operationLED1 FAST FLASH / LED2 FAST FLASH (simultaneous)Normal operation signaled when heating demand initiated at thermostat.LED1 Fast Flash / LED2 Slow FlashMain power polarity reversed (-5 and -6 models SureLight)LED1 Off / LED2 OnCircuit board failure or control wired incorrectly (-5 and -6 models SureLight).LED1 Off / LED2 Slow FlashPressure switch open or has opened 5 times during a single call for heat; or…LED1 On / LED2 OffCircuit board failure or control wired incorrectly (-5 and -6 models SureLight).LED1 ON / LED2 ONCircuit board failure or control wired incorrectlyLED1 ON / LED2 SLOW FLASHFlame sensed without gas valve energized, or rollout switch open, or low…LED1 Simultaneous Fast Flash / LED2 Simultaneous Fast FlashNormal operationLED1 Simultaneous Slow Flash / LED2 Simultaneous Slow FlashPower on, normal operation; also signaled during cooling and continuous fan (-5…LED1 SLOW FLASH / LED2 FAST FLASHLow flame signalLED1 SLOW FLASH / LED2 OFFPrimary or secondary limit switch openLED1 SLOW FLASH / LED2 SLOW FLASHPower onLED1 SLOW FLASH / LED2 SLOW FLASH (simultaneous)Power on, normal operation; also signaled during cooling and continuous fan.LED1-ALT_FAST_FLASH/LED2-ALT_FAST_FLASHImproper main ground or line voltage below 75 volts; OR broken ignitor; OR open…LED1-ALT_SLOW_FLASH/LED2-ALT_SLOW_FLASHWatchguardLED1-FAST_FLASH/LED2-FAST_FLASHNormal operationLED1-FAST_FLASH/LED2-SLOW_FLASHMain power polarity reversedLED1-OFF/LED2-SLOW_FLASHPressure switch open or has opened 5 times during a single call for heat; OR…LED1-ON/LED2-SLOW_FLASHRollout switch open OR 9-pin connector improperly attached.LED1-SLOW FLASH / LED2-ONPrimary or secondary limit open. Units with board 12L42LED1-SLOW_FLASH/LED2-FAST_FLASHLow flame signalLED1-SLOW_FLASH/LED2-OFFFlame sensed without gas valve energized.LED1-SLOW_FLASH/LED2-ONPrimary or secondary limit open. Units with board 63K8901 or 24L85LED1-SLOW_FLASH/LED2-SLOW_FLASHPower onLED1: Alternating Fast Flash / LED2: Alternating Fast FlashImproper main ground (sensed during ignitor warm up on controls…LED1: Alternating Slow Flash / LED2: Alternating Slow FlashWatchguardLED1: Fast Flash / LED2: Slow FlashMain power polarity reversedLED1: OFF / LED2: ONMain power polarity reversedLED1: OFF / LED2: Slow FlashPressure switch open or has opened 5 times during a single call for heat; OR…LED1: ON / LED2: OFFFlame sensed without gas valve energized (duplicate indication with…LED1: ON / LED2: ONCircuit board failure or control wired incorrectly.LED1: ON / LED2: Slow FlashFlame sensed without gas valve energized, or rollout switch open, or 24V pin…LED1: Simultaneous Fast Flash / LED2: Simultaneous Fast FlashNormal operationLED1: Simultaneous Slow Flash / LED2: Simultaneous Slow FlashPower onLED1: Slow Flash / LED2: Fast FlashLow flame signalLED1: Slow Flash / LED2: OFFFlame sensed without gas valve energized.LED1: Slow Flash / LED2: ONPrimary or secondary limit open; limit must close within specified time or…OffNo power to control or board fault detected.OnBoard fault detected.PulsePower onSIMULTANEOUS FAST FLASHNormal operationSIMULTANEOUS SLOW FLASHPower onSlow Flash (RAM)Normal operation, no call for heat (RAM control).Steady ON (RAM)Control board failure (RAM control).