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Lennox HVAC Error Codes
36 error codes for Lennox hvac models. Each links to the full diagnostic procedure from the service manual.
CodeDescription
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…104There is a delay in the air-handler responding to the system.105The iComfort thermostat has lost communication with the air-handler for more…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 FlashesLockout201The 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…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…MyPros+ Max
Get the full diagnostic procedure for any Lennox hvac error code.
- Step-by-step tests with expected resistance, voltage, and continuity values
- Wiring diagram references and connector pinouts
- Verified part numbers when replacement is required
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301The O relay on the air-handler has failed (pilot relay contacts did not close…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…304The Y2 relay on the air-handler has failed (pilot relay contacts did not close…350The air-handler's electric heat is not configured.351There is a problem with the air-handler's first stage electric heat (pilot…352There is a problem with the air-handler's second stage electric heat (pilot…353There is a problem with the air-handler's third stage electric heat (pilot…354There is a problem with the air-handler's fourth stage electric heat (pilot…355There is a problem with the air-handler's fifth stage electric heat (pilot…4 FlashesHigh limit or rollout switch open.401The secondary voltage for the air-handler has fallen below 18VAC; if this…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.