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Error code reference
Lennox HVAC Error Codes
36 error codes documented with diagnostic procedures.
Have your model number? Get codes specific to your unit.
101The air-handler has lost communication with the rest of the system.102There is a frequency/distortion problem with the power to the air-handler.103The 24VAC to the air-handler control is lower than the required range of 18 to 30VAC.104There is a delay in the air-handler responding to the system.105The iComfort thermostat has lost communication with the air-handler for more than 3…106There is a hardware problem with the air-handler control.130An air-handler configuration jumper is missing.131The air-handler control parameters are corrupted.132The air-handler control software is corrupted.133The iComfort thermostat has found a problem with the air-handler outdoor sensor.2 FlashesLockout-failed to detect or sustain flame.201The system has lost communication with the air-handler indoor blower motor.202The unit size code for the air-handler and the size of blower motor do not match.203The unit size code for the air-handler has not been selected.204The air-handler's blower motor will not start.205The indoor blower motor is overheating (motor tripped on internal protector).206There is a problem with the air-handler discharge air sensor.207The blower cannot provide the requested CFM due to high static (cutback mode).208The indoor and outdoor unit capacities do not match.3 FlashesPressure switch open or closed, or auxiliary limit open (code will not appear until after…301The O relay on the air-handler has failed (pilot relay contacts did not close or relay…302The R to O jumper was not removed on the air-handler control board.303The Y1 relay on the air-handler has failed (pilot relay contacts did not close or relay…304The Y2 relay on the air-handler has failed (pilot relay contacts did not close or relay…350The air-handler's electric heat is not configured.351There is a problem with the air-handler's first stage electric heat (pilot relay contacts…352There is a problem with the air-handler's second stage electric heat (pilot relay…353There is a problem with the air-handler's third stage electric heat (pilot relay contacts…354There is a problem with the air-handler's fourth stage electric heat (pilot relay…355There is a problem with the air-handler's fifth stage electric heat (pilot relay contacts…4 FlashesHigh limit or rollout switch open.401The secondary voltage for the air-handler has fallen below 18VAC; if this continues for…5 FlashesFlame sensed and gas valve not energized.Fast FlashNormal operation, call for heat.Slow FlashNormal operation, no call for heat.Steady FlashCircuit board self-check failure or ignition/blower control wired incorrectly.
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Common questions
How do I find the error code on my Lennox HVAC?
Most Lennox hvacs show the code directly on the control panel display. If your model has no display, it can be read by entering diagnostic mode with the key sequence for your model. The full procedures include model-specific instructions for reading codes.
Are these codes specific to my model?
The codes here apply broadly to Lennox hvacs. Meanings and diagnostic steps can vary by model and production year, so enter your model number for model-specific information and procedures.
What do I do if my code is not listed?
Some codes are model-specific or only appear in diagnostic mode. Enter your model number to get codes specific to your unit, or contact us. We update the database continuously from manufacturer service documentation.
How much does it cost to access the full diagnostic procedures?
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