Lennox Furnace & AC Error Codes

Below is a complete list of Lennox furnace and air conditioner diagnostic error codes . Each code includes what it means, safe DIY checks you can try, when to call a professional, and estimated repair costs.

How to Read Lennox Error Codes

For newer Lennox models: look through the sight glass on the furnace panel for a digital display showing an E-code (like E228). For older models: look for two LEDs (often red and green) on the control board. Count the number of flashes of each LED. Both LEDs blinking simultaneously (fast or slow) means normal operation. Alternating red and green flashes indicate a fault — the pattern of red vs green flashes indicates the specific error.

LED Location: Visible through the sight glass on the lower access panel. Newer models (SLP98, EL296, etc.) have a digital display on the control board. Older models have red and green LEDs labeled DS1 and DS2.

Code Format: Newer models use digital E-codes on the control board display (e.g., E228, E250). Older models use red/green LED flash patterns where the number of flashes indicates the error. Some models have both.

Safety Warning

1 emergency code(s) require immediate professional attention. 7 high-urgency code(s) should be addressed promptly. If you smell gas, hear unusual sounds, or see sparks, turn off the system and call a professional immediately.

Quick Navigation — 14 Error Codes

Error E228 Error E250 Error E270 Error E276 Error E290 Error E292 1 Red Flash 2 Red Flashes 4 Red Flashes 5 Red Flashes 6 Red Flashes 8 Red Flashes 10 Red Flashes Red and Green Alternating

Lennox Error E228: Pressure switch calibration failure

Medium Urgency

The furnace control board was unable to successfully calibrate the pressure switch during the startup sequence. Lennox high-efficiency furnaces perform a pressure switch calibration each time the furnace starts to verify proper venting.

Estimated repair cost: $200 – $600

Common Causes

  • Blocked exhaust or intake vent pipe (ice, snow, leaves, bird nests)
  • Failing or weak inducer motor not generating consistent draft
  • Faulty pressure switch that cannot calibrate within the expected range
  • Clogged condensate drain or trap creating back-pressure

DIY Troubleshooting Steps

  1. Check both the exhaust and intake PVC pipes outside your home for blockages — clear any ice, snow, or debris
  2. Check the condensate drain line for clogs — pour warm water through to clear the line and trap
  3. Make sure the small rubber hose connecting the pressure switch to the inducer housing is not cracked or kinked

Call a professional when: The vents are clear and the drain is flowing freely but the E228 code persists. This often indicates a failing inducer motor, defective pressure switch, or a control board issue that requires professional diagnosis.

Lennox Error E250: Ignition failure — failed to light

High Urgency

The furnace attempted to ignite but failed to establish a flame. After multiple retry attempts, the system has locked out. This is one of the most common Lennox error codes.

Estimated repair cost: $150 – $450

Common Causes

  • Dirty or corroded flame sensor not detecting the flame
  • Failed or cracked hot surface igniter
  • Gas supply interruption (closed valve, empty propane, utility issue)
  • Defective gas valve not opening

DIY Troubleshooting Steps

  1. Verify the gas supply is on — check the manual shut-off valve near the furnace (handle parallel to pipe = on)
  2. Clean the flame sensor with fine steel wool or emery cloth (turn off power first)
  3. Try resetting the furnace by turning power off for 30 seconds, then back on

Call a professional when: The code returns after reset and flame sensor cleaning. A technician needs to test the igniter, verify gas pressure, and check the gas valve operation.

Lennox Error E270: Pressure switch fault during operation

Medium Urgency

The pressure switch opened during the furnace operation, indicating a loss of proper venting draft while the furnace was running. This differs from E228 (calibration failure) because it occurs mid-cycle.

Estimated repair cost: $200 – $550

Common Causes

  • Intermittent exhaust vent blockage (wind gusts, shifting debris)
  • Weak inducer motor that cannot maintain consistent draft
  • Failing pressure switch with intermittent contact
  • Condensate drain partially clogged causing intermittent backup

DIY Troubleshooting Steps

  1. Check exhaust and intake vent pipes outside for partial blockages
  2. Clear the condensate drain line — partial clogs can cause intermittent issues
  3. Check that no dryer vents or other exhaust vents are near the furnace intake pipe

Call a professional when: The code keeps appearing during operation. Intermittent pressure switch faults often indicate a failing inducer motor, worn pressure switch, or a developing heat exchanger issue.

Lennox Error E276: Exceeded maximum pressure switch calibration retries

Medium Urgency

The furnace has exceeded the maximum number of pressure switch calibration attempts and entered a soft lockout. This is often seen alongside E228 and means the system has given up trying to calibrate the pressure switch.

Estimated repair cost: $200 – $600

Common Causes

  • Persistent vent blockage that was not cleared
  • Inducer motor degrading and providing inconsistent vacuum levels
  • Defective pressure switch providing erratic readings
  • Water in the pressure switch hose or port

DIY Troubleshooting Steps

  1. Perform all the same checks as E228 — clear vents, check condensate drain, inspect pressure hose
  2. Reset the furnace by turning power off for 30 seconds and back on to clear the soft lockout

Call a professional when: The code appears repeatedly after clearing vents and resetting. A technician needs to test the inducer motor performance and pressure switch operation with a manometer.

Lennox Error E290: Indoor blower motor unable to reach target speed

Medium Urgency

The blower motor (ECM/variable-speed motor) cannot achieve its target RPM. The motor is running but not at the speed the control board is requesting.

Estimated repair cost: $200 – $1,500

Common Causes

  • Extremely dirty blower wheel creating excessive drag on the motor
  • Dirty or clogged air filter causing high static pressure
  • Collapsed or blocked ductwork creating excessive resistance
  • Failing blower motor with worn bearings

DIY Troubleshooting Steps

  1. Replace the air filter immediately — a heavily clogged filter is the most common cause
  2. Make sure all supply and return vents are open and unobstructed
  3. Check if the blower wheel is visibly dirty by looking into the blower compartment (turn off power first)

Call a professional when: The code persists after changing the filter and opening vents. The blower wheel likely needs professional cleaning, or the motor may be failing and need replacement.

Lennox Error E292: Indoor blower motor unable to start

High Urgency

The blower motor has completely failed to start. The control board is sending the signal to run, but the motor is not responding. The furnace cannot operate without the blower to distribute air.

Estimated repair cost: $400 – $2,000

Common Causes

  • Seized blower motor due to failed bearings
  • Obstructed blower wheel (debris, loose parts preventing rotation)
  • Failed blower motor electrical windings
  • Wiring fault between the control board and blower motor

DIY Troubleshooting Steps

  1. Turn off power and check if the blower wheel can be spun freely by hand — if it is stuck, something is obstructing it
  2. Check for any debris or foreign objects that may have fallen into the blower compartment

Call a professional when: The motor does not spin freely or the code persists. A seized or failed motor requires professional replacement. ECM/variable-speed motor replacements are complex and should not be attempted as a DIY repair.

Lennox 1 Red Flash: System lockout — ignition failure

High Urgency

On older Lennox models using LED flash codes, one red flash in a repeating pattern indicates the furnace has entered lockout mode due to repeated ignition failures. The system tried to light multiple times and failed.

Estimated repair cost: $150 – $400

Common Causes

  • Failed hot surface igniter
  • Dirty flame sensor
  • Gas supply issue (valve off, low pressure)
  • Defective gas valve

DIY Troubleshooting Steps

  1. Reset the furnace by turning power off for 30 seconds, then back on
  2. Verify gas supply is on — check the manual shut-off valve near the furnace
  3. Clean the flame sensor with fine steel wool (turn off power first)

Call a professional when: The lockout returns after resetting. A technician can test the igniter, measure gas pressure, and diagnose the specific failure.

Lennox 2 Red Flashes: Pressure switch stuck closed

Medium Urgency

The pressure switch is stuck in the closed position when it should be open. This indicates the switch may be mechanically faulty or there is a wiring issue.

Estimated repair cost: $150 – $400

Common Causes

  • Defective pressure switch with welded contacts
  • Short circuit in the pressure switch wiring
  • Residual vacuum in the vent system holding the switch closed

DIY Troubleshooting Steps

  1. Check the small rubber hose connected to the pressure switch for obstructions
  2. Try resetting the furnace by cycling power off for 30 seconds

Call a professional when: This code requires a technician to test and likely replace the pressure switch. Bypassing the pressure switch is dangerous and should never be done.

Lennox 4 Red Flashes: High-limit switch open — furnace overheating

High Urgency

The high-temperature limit switch has tripped due to the furnace overheating. This safety device prevents heat exchanger damage and fire hazard.

Estimated repair cost: $150 – $600

Common Causes

  • Dirty or clogged air filter restricting airflow
  • Blocked supply or return registers
  • Failed blower motor or bad capacitor
  • Dirty blower wheel reducing air volume

DIY Troubleshooting Steps

  1. Replace the air filter immediately
  2. Open all supply and return registers in the home
  3. Verify the blower motor is running — listen for it or feel for airflow at the vents

Call a professional when: The limit switch keeps tripping after replacing the filter and opening vents. The blower motor, capacitor, or blower wheel likely needs professional attention.

Lennox 5 Red Flashes: Flame rollout switch tripped

Emergency

The flame rollout switch has detected flames or excessive heat outside of the normal burner area. This is a serious safety condition — flames are escaping the combustion chamber.

Estimated repair cost: $300 – $3,000

Common Causes

  • Cracked heat exchanger allowing flames to escape
  • Blocked exhaust vent causing combustion gas backup
  • Blocked heat exchanger passages
  • Excessive gas pressure

DIY Troubleshooting Steps

  1. Check the exhaust vent outside for blockages
  2. Do NOT attempt to reset the flame rollout switch — it trips for a critical safety reason

Call a professional when: Always call a professional immediately for a flame rollout condition. This can indicate a cracked heat exchanger, which poses a carbon monoxide poisoning risk. The furnace should not be operated until inspected.

Lennox 6 Red Flashes: Pressure switch failure — did not close

Medium Urgency

The pressure switch did not close when the inducer motor started, indicating insufficient draft for safe operation.

Estimated repair cost: $150 – $500

Common Causes

  • Blocked exhaust or intake vent pipe
  • Failing inducer motor
  • Cracked or disconnected pressure hose
  • Clogged condensate drain

DIY Troubleshooting Steps

  1. Check exhaust and intake pipes outside for blockages (ice, debris, animal nests)
  2. Inspect the condensate drain line for clogs
  3. Check the pressure switch hose for cracks or disconnection

Call a professional when: The vents are clear and hose is intact but the code persists. The inducer motor or pressure switch likely needs professional testing or replacement.

Lennox 8 Red Flashes: Ignition lockout — multiple failed attempts

High Urgency

The furnace has entered a hard lockout after multiple failed attempts to ignite. The system will not retry without a manual reset.

Estimated repair cost: $150 – $450

Common Causes

  • Failed hot surface igniter
  • Dirty or defective flame sensor
  • Gas supply issue
  • Defective gas valve

DIY Troubleshooting Steps

  1. Reset the furnace by cycling power off for 30 seconds
  2. Clean the flame sensor
  3. Verify gas supply is on

Call a professional when: The lockout returns after reset. Repeated ignition failure requires professional testing of the igniter, gas pressure, and valve.

Lennox 10 Red Flashes: High-stage limit switch open (two-stage models)

High Urgency

On two-stage Lennox furnaces, the high-stage limit switch has tripped, indicating overheating specifically during high-stage (high-fire) operation.

Estimated repair cost: $150 – $600

Common Causes

  • Dirty air filter restricting airflow during high-stage operation
  • Undersized ductwork unable to handle high-stage BTU output
  • Blower motor not ramping to high-speed properly
  • High-stage gas pressure set too high

DIY Troubleshooting Steps

  1. Replace the air filter immediately
  2. Open all vents and registers in the home

Call a professional when: The code persists after filter change. A technician needs to verify ductwork sizing, blower motor high-speed operation, and high-stage gas pressure settings.

Lennox Red and Green Alternating: Reversed line voltage polarity

High Urgency

The red and green LEDs are alternating, indicating the 115V line voltage polarity is reversed (hot and neutral are swapped).

Estimated repair cost: $100 – $250

Common Causes

  • Reversed wiring at the furnace junction box
  • Faulty outlet or disconnect switch wired incorrectly
  • Recent electrical work affecting the furnace circuit

DIY Troubleshooting Steps

  1. If recent electrical work was done, contact the electrician who performed it
  2. Do not attempt to rewire the furnace yourself

Call a professional when: Always call a licensed electrician or HVAC technician. Reversed polarity is an electrical hazard that must be corrected.

Need Lennox Repair in Central Texas?

Texas Temp Masters provides expert HVAC repair for Lennox and all major brands in Killeen, Waco, Temple, and surrounding areas. Call (817) 704-0706 for fast, reliable service, or contact us online.

Error code information cross-referenced from manufacturer documentation, HVAC/appliance professional resources, and verified repair databases. Codes can vary by specific model and control board revision. Always verify against your unit's diagnostic label or owner's manual. Repair costs are estimates based on national averages. Last updated February 2026.

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