Low Flame Signal - check flame sensor.
First step from the service manual
1
Clean flame sensor with steel wool; measure flame signal (should be 1.5 microamps or greater).
The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.
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Low Flame Signal - check flame sensor
From Service Manual 723190, p.42:
1.Clean flame sensor with steel wool; measure flame signal (should be 1.5 microamps or greater).
2.Measure control board supply voltage at the test points. Expected: 12 VDC and 5 VDC; a drop below 4.75 VDC on the logic rail points to a failed onboard regulator.
3.Inspect all connectors on the main control for corrosion, thermal stress, or backed-out pins. Reseat each connector with the power disconnected.
Part WPW10804018
Electronic control board
Related Lennox furnace codes
All Lennox furnace codes →- 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 sequence
- 10Watchguard
- 11Pressure switch stuck closed prior to activation of…
- 2Improper Earth Ground.
- 2 FlashesPressure switch closed with combustion air inducer…
View all 213 Lennox furnace codes
- 2 Flashes (RAM)Control lockout
- 2+3Low fire pressure switch sensed open; 80%
- 2+4Low fire pressure switch sensed closed prior to activation…
- 2+5High fire pressure switch sensed open. 80%
- 2+6High fire pressure switch sensed closed prior to activation…
- 2+7Low pressure switch opened during ignition trial or heating…
- 3Burner failed to light, or lost flame during heat demand.
- 3 FlashesPressure switch open with combustion air inducer energized…
- 3 Flashes (RAM)Pressure switch open
- 3+1Limit switch open (primary or secondary).
- 4 FlashesPrimary limit switch open (Control 103085).
- 4 Flashes (RAM)Open limit
- 4+1Watchguard
- 4+2Watchguard
- 4+3Watchguard
- 4+5Watchguard
- 4+6Watchguard
- 4+7Watchguard
- 4+8Low line voltage (below 90 volts for board 100870).
- 5Watchguard
- 5 FlashesRollout switch open (control 103085).
- 5 Flashes (RAM)Flame sensed and gas valve not energized.
- 5+1Hard lockout
- 5+2Control failed self check, internal error; control will…
- 5+3No Earth ground; control will restart if error recovers…
- 5+4Reversed line voltage polarity; control will restart if the…
- 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 Mode
- 7 FLASHESLockout
- 8Rollout switch open.
- 8 FlashesLockout
- 9Pressure Switch failed to close or opened during heat…
- 9 FlashesLine voltage polarity incorrect (Control 103085).
- DIAG#1: Alternate Flash / DIAG#2: Alternate FlashWatchguard
- DIAG#1: Continuous On / DIAG#2: Continuous OnCircuit board self-check failure or ignition/blower control…
- DIAG#1: Flash / DIAG#2: OffPressure switch Watchguard
- DIAG#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…
- DS1 Alternating Fast Flash / DS2 Alternating Fast FlashDuring ignitor warm-up period only
- DS1 Alternating Slow Flash / DS2 Alternating Slow FlashWatchguard
- DS1 Fast Flash / DS2 Fast FlashNormal operation
- DS1 Fast Flash / DS2 Fast Flash (simultaneous)Normal operation
- DS1 Fast Flash / DS2 Slow FlashDuring ignitor warm-up period only
- DS1 OFF / DS2 Fast FlashHigh pressure switch open, or blocked inlet/exhaust vent…
- DS1 Off / DS2 OnLow flame signal; measures below 0.23 microAmps
- DS1 OFF / DS2 Slow FlashLow pressure switch open, or blocked inlet/exhaust vent, or…
- DS1 On / DS2 OffMain power polarity reversed; switch line and neutral.
- DS1 On / DS2 OnCircuit board failure or control wired incorrectly; check…
- DS1 Slow Flash / DS2 Fast FlashLow flame signal
- DS1 Slow Flash / DS2 OffFlame sensed without gas valve energized.
- DS1 Slow Flash / DS2 ONPrimary, secondary, backup secondary or rollout limit…
- DS1 Slow Flash / DS2 Slow FlashPower on
- DS1 Slow Flash / DS2 Slow Flash (simultaneous)Power on
- DS1/DS2 Alternating Fast FlashDuring ignitor warm-up only
- DS1/DS2 Alternating Slow FlashWatchguard
- E 111Line voltage polarity reversed.
- E 114Line voltage frequency out-of-range (no 60 Hertz power).
- E 117Poor ground detected (warning only).
- E 125Control failed self-check, internal error, failed hardware…
- E 226High pressure switch failed closed.
- E 227Low pressure switch open during trial for ignition or run…
- E 240Low flame current during run mode.
- E 250Limit switch circuit open.
- E 271Soft lockout
- E 272Soft lockout
- E 273Soft lockout
- E 274Soft lockout
- E 290Ignitor circuit fault
- E105Device communication problem
- E110Low line voltage detected (voltage lower than nameplate…
- E112Ground not detected; system shuts down.
- E113High line voltage detected (voltage higher than nameplate…
- E115Low 24V power (range is 18 to 30 volts); control will…
- E116High 24V (range is 18 to 30 volts).
- E120Unresponsive device (communication only), usually caused by…
- E124Active communicating thermostat signal missing for more…
- E126Control internal communication problem.
- E131Corrupted control parameters (communicating only).
- E180Outdoor air temperature sensor failure (shorted or…
- E200Device communication problem
- E201Indoor blower communication failure
- E202Indoor blower motor mis-match
- E203Appliance capacity/size is NOT programmed; invalid unit…
- E204Line voltage frequency out-of-range; no 60 hertz power.
- E205Low 24V
- E206Indoor blower motor mis-match
- E207Hot surface ignitor sensed open.
- E208Gas valve mis-wired.
- E209Gas valve control relay contact shorted.
- E210Unresponsive device; usually caused by delay in outdoor…
- E211Active communicating thermostat signal missing for more…
- E212Control failed self-check, internal error, failed hardware…
- E213Failed internal control communication between…
- E214Corrupted control parameters (verify configuration of…
- E215Outdoor air sensor failure
- E218Indoor blower communication failure
- E220Hard lockout
- E221Low pressure switch failed open.
- E222Low pressure switch failed closed.
- E223High pressure switch failed open.
- E224Low pressure switch failed closed (stuck closed on heat…
- E225Low pressure switch open during trial for ignition or run…
- E228Unable to perform successful pressure switch calibration.
- E229Ignition on High Fire
- E241Flame sensed out of sequence
- E251Discharge air temperature too high (gas heat only).
- E252Discharge air temperature too high (gas heat only).
- E260Soft lockout
- E261Soft lockout
- E262Soft lockout
- E263Soft lockout
- E264Soft lockout
- E265Soft lockout
- E266Soft lockout
- E269Ignitor circuit fault
- E270Restricted air flow
- E275Heat rate reduced to match indoor blower air flow; furnace…
- E276Restricted air flow in cooling or continuous fan mode is…
- E277Indoor or outdoor unit capacity mismatch.
- E278Global network connection
- E280No 24 Volt output on Y1 to C with non-communicating outdoor…
- E281No 24 Volt output on Y2 to C with non-communicating outdoor…
- E282No 24 Volts between R & O with non-communicating outdoor…
- E291Heat air flow restricted below the minimum.
- E292Indoor blower motor unable to start due to obstructed wheel…
- E294Combustion air inducer over current.
- E295Indoor blower motor temperature is too high (motor tripped…
- E300LSOM
- E301LSOM
- E302LSOM
- E303LSOM
- E304LSOM
- E305LSOM
- E306LSOM
- E307LSOM
- E308LSOM
- E310Discharge air temperature sensor failure (shorted or out of…
- E311Heat rate reduced to match indoor blower air flow (furnace…
- E312Restricted air flow in cooling or continuous fan mode is…
- E313Indoor or outdoor unit capacity mismatch (communication…
- E331Global network connection
- E334Relay Y1 stuck on integrated control.
- E347No 24 Volt output on Y1 of integrated control with…
- E348No 24 Volt output on Y2 of integrated control with…
- E349No 24 Volts between R & O on integrated control with…
- E370Interlock switch sensed open for 2 minutes.
- E400LSOM
- E401LSOM
- E402LSOM
- E403LSOM
- E404LSOM
- E405LSOM
- E406LSOM
- E407LSOM
- E408LSOM
- E409LSOM
- Fast Flash (RAM)Normal operation with call for heat (RAM control).
- HeartbeatNormal operation
- LED Flashing 1/2 sec on 1/2 sec offLockout or Restricted Lockout condition on the R7184B…
- LED Flashing 2 sec on 2 sec offBurner control is in Recycle mode
- LED OnFlame sensed by the R7184B burner control (cad cell…
- LED Slow FlashControl retry period
- LED Steady OnNormal operation of the G776 ignition control (-1 through…
- LED-OFFControl failure or power failure or hard lockout (G776…
- LED-SLOW_FLASH_1ON_5OFFControl retry period
- LED-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 only
- LED#1 Alternating Slow Flash / LED#2 Alternating Slow FlashWatchguard
- LED#1 Fast Flash / LED#2 Fast Flash (simultaneous)Normal operation, signaled when heating demand initiated at…
- LED#1 Fast Flash / LED#2 Slow FlashMain power polarity reversed
- LED#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…
- 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…
- LED#1 Simultaneous Fast Flash / LED#2 Simultaneous Fast FlashNormal operation
- LED#1 Simultaneous Slow Flash / LED#2 Simultaneous Slow FlashPower on, normal operation; also signaled during cooling…
- LED#1 Slow Flash / LED#2 Fast FlashLow flame signal
- LED#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…
- LED#1 Slow Flash / LED#2 Slow Flash (simultaneous)Power on, normal operation; also signaled during cooling…
- LED1 ALT FAST FLASH / LED2 ALT FAST FLASHDuring ignitor warm-up
- LED1 ALT SLOW FLASH / LED2 ALT SLOW FLASHWatchguard
- LED1 FAST FLASH / LED2 FAST FLASHNormal operation
- LED1 SLOW FLASH / LED2 SLOW FLASHPower on
- LED1-ALT_FAST_FLASH/LED2-ALT_FAST_FLASHImproper main ground or line voltage below 75 volts; OR…
- LED1-ALT_SLOW_FLASH/LED2-ALT_SLOW_FLASHWatchguard
- LED1-FAST_FLASH/LED2-FAST_FLASHNormal operation
- LED1-FAST_FLASH/LED2-SLOW_FLASHMain power polarity reversed
- LED1-OFF/LED2-SLOW_FLASHPressure switch open or has opened 5 times during a single…
- LED1-ON/LED2-SLOW_FLASHRollout switch open OR 9-pin connector improperly attached.
- LED1-SLOW_FLASH/LED2-FAST_FLASHLow flame signal
- LED1-SLOW_FLASH/LED2-OFFFlame sensed without gas valve energized.
- LED1-SLOW_FLASH/LED2-ONPrimary or secondary limit open. Units with board 63K8901…
- LED1-SLOW_FLASH/LED2-SLOW_FLASHPower on
- OffNo power to control or board fault detected.
- OnBoard fault detected.
- PulsePower on
- SIMULTANEOUS FAST FLASHNormal operation
- SIMULTANEOUS SLOW FLASHPower on
- Slow Flash (RAM)Normal operation, no call for heat (RAM control).
- Steady ON (RAM)Control board failure (RAM control).
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