Lennox Split & Multi-Split

Lennox Split & Multi-Split Error Code E124

Split & Multi-Split

E124 means different things on different Split & Multi-Split models. Enter your model number to see only your reading, or find your model below.

What It Means

  • The iComfort thermostat has lost communication with the outdoor unit for more than 3 minutes.
  • The S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.
  • CBX40UHV: Active Subnet Controller Missing for > 180 seconds. This indicates a data connection has been lost between a communicating device and the communicating thermostat. Device (indoor or outdoor unit) sends the alarm if no communication is established between device and thermostat within three minutes.
  • Equipment lost communication
  • CBK48MVT: The iComfort thermostat has lost communication with the air-handler for more than 3 minutes.

Causes & actions from Lennox

The iComfort thermostat has lost communication with the outdoor unit for more than 3 minutes.

35 models

EL18XCV, EL18XCV-024, EL18XCV-036, EL18XCV-048, EL18XCV-060, EL18XPV, EL18XPV-024, EL18XPV-036, EL18XPV-048, EL18XPV-060, EL19KPV, EL19KPV-024, EL19KPV-036, EL19KPV-048, EL19KPV-060, EL21KLV, EL21KLV-024, EL21KLV-036, EL21KLV-048, EL21KLV-060, EL22KCV, EL22KCV-024, EL22KCV-036, EL22KCV-048, EL22KCV-060, SL22KLV, SL22KLV-024, SL22KLV-036, SL22KLV-048, SL22KLV-060, SL25KCV, SL25KCV-024, SL25KCV-036, SL25KCV-048, SL25KCV-060

Heat pump (outdoor)

How it shows
  • Outdoor control 7-segment display: E124

Equipment lost communication with the thermostat. Check the wiring connections and resistance, then cycle the system power. This alarm stops all associated HVAC operations and waits for a signal from the non-communicating unit. The alarm / fault clears after communication is re-established.

Other manual wording

EL18XCV, EL18XCV-024, EL18XCV-036, EL18XCV-048, EL18XCV-060, EL18XPV, EL18XPV-024, EL18XPV-036, EL18XPV-048, EL18XPV-060, EL19KPV,…

Equipment lost communication with the thermostat. Check the wiring connections, ohm wires and cycle power. The alarm stops all associated HVAC operations and waits for a heartbeat message from the unit that's not communicating. The alarm / fault clears after communication is re-established.

Applicable models & manual sources
  • EL18XCV

    The iComfort S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL18XCV, EL18XCV-024, EL18XCV-036, EL18XCV-048, EL18XCV-060

    EL18XCV manual, page 36

  • EL18XPV

    The iComfort S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL18XPV, EL18XPV-024, EL18XPV-036, EL18XPV-048, EL18XPV-060

    EL18XPV manual, page 36

  • EL19KPV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL19KPV, EL19KPV-024, EL19KPV-036, EL19KPV-048, EL19KPV-060

    EL19KPV manual, page 42

  • EL21KLV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL21KLV, EL21KLV-024, EL21KLV-036, EL21KLV-048, EL21KLV-060

    EL21KLV manual, page 45

  • EL22KCV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL22KCV, EL22KCV-024, EL22KCV-036, EL22KCV-048, EL22KCV-060

    EL22KCV manual, page 39

  • SL22KLV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL22KLV, SL22KLV-024, SL22KLV-036, SL22KLV-048, SL22KLV-060

    SL22KLV manual, page 42

  • SL25KCV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL25KCV, SL25KCV-024, SL25KCV-036, SL25KCV-048, SL25KCV-060

    SL25KCV manual, page 36

  • EL18XCV

    The iComfort S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL18XCV, EL18XCV-024, EL18XCV-036, EL18XCV-048, EL18XCV-060

    EL18XCV manual, page 72

  • EL18XPV

    The iComfort S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL18XPV, EL18XPV-024, EL18XPV-036, EL18XPV-048, EL18XPV-060

    EL18XPV manual, page 75

  • EL19KPV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL19KPV, EL19KPV-024, EL19KPV-036, EL19KPV-048, EL19KPV-060

    EL19KPV manual, page 77

  • EL22KCV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    EL22KCV, EL22KCV-024, EL22KCV-036, EL22KCV-048, EL22KCV-060

    EL22KCV manual, page 72

  • SL22KLV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL22KLV, SL22KLV-024, SL22KLV-036, SL22KLV-048, SL22KLV-060

    SL22KLV manual, page 81

  • SL25KCV

    The S40 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL25KCV, SL25KCV-024, SL25KCV-036, SL25KCV-048, SL25KCV-060

    SL25KCV manual, page 67

The S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

5 models

SL28XCV, SL28XCV-024, SL28XCV-036, SL28XCV-048, SL28XCV-060

Air conditioner (outdoor)

How it shows
  • Outdoor control 7-segment display: E124

Equipment lost communication with the thermostat. Check the wiring connections and resistance, then cycle the system power. This alarm stops all associated HVAC operations and waits for a signal from the non-communicating unit. The alarm / fault clears after communication is re-established.

Other manual wording

SL28XCV, SL28XCV-024, SL28XCV-036, SL28XCV-048, SL28XCV-060

Equipment lost communication with the thermostat. Check the wiring connections, ohm wires and cycle power. The alarm stops all associated HVAC operations and waits for a heartbeat message from the unit that's not communicating. The alarm / fault clears after communication is re-established.

Applicable models & manual sources
  • SL28XCV

    The S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL28XCV, SL28XCV-024, SL28XCV-036, SL28XCV-048, SL28XCV-060

    SL28XCV manual, page 30

  • SL28XCV

    The S30 thermostat has lost communication with the outdoor unit for more than 3 minutes.

    SL28XCV, SL28XCV-024, SL28XCV-036, SL28XCV-048, SL28XCV-060

    SL28XCV manual, page 61

Active Subnet Controller Missing for > 180 seconds. This indicates a data connection has been lost between a communicating device and the communicating thermostat. Device (indoor or outdoor unit) sends the alarm if no communication is established between device and thermostat within three minutes.

Models: CBX40UHV

Air handler (indoor)

How it shows
  • Single-character display: E124

Active Subnet Controller Missing for > 180 seconds. This indicates a data connection has been lost between a communicating device and the communicating thermostat. Device (indoor or outdoor unit) sends the alarm if no communication is established between device and thermostat within three minutes.

Applicable models & manual sources
  • CBX40UHV

    Active Subnet Controller Missing for > 180 seconds. This indicates a data connection has been lost between a communicating device and the communicating thermostat. Device (indoor or outdoor unit) sends the alarm if no communication is established be- tween device and thermostat within three minutes.

    CBX40UHV manual, page 21

Equipment lost communication

5 models

EL21KLV, EL21KLV-024, EL21KLV-036, EL21KLV-048, EL21KLV-060

Heat pump (outdoor)

How it shows
  • Outdoor control 7-segment display: E124

The thermostat has lost communication with a system component for more than three minutes. System component has lost communication with the thermostat. • Check the wiring connections between components. • Ohm wires. • Cycle power. • Any component that is miss-wired may cause a false component code to be shown on system component. • Disconnect all wiring to other system components and check communication one at a time. NOTE: When using a float switch, use isolation relay to break common wire to outdoor unit. For testing purposes, remove float switch from the circuit This alert code stops all associated system operations and waits for a heartbeat message from the system component that is not communicating.

Applicable models & manual sources
  • EL21KLV

    Equipment lost communication

    EL21KLV, EL21KLV-024, EL21KLV-036, EL21KLV-048, EL21KLV-060

    EL21KLV manual, page 86

The iComfort thermostat has lost communication with the air-handler for more than 3 minutes.

Models: CBK48MVT

How it shows
  • Single-character display: E124

Equipment lost communication with the icomfort thermostat. Check the wiring con- nections, ohm wires and cycle power. The alarm stops all associated HVAC operations and waits for a heartbeat message from the unit that's not communicating. The alarm/ fault clears after communication is re-established.

Applicable models & manual sources
  • CBK48MVT

    The iComfort thermostat has lost com- munication with the air-handler for more than 3 minutes.

    CBK48MVT manual, page 51

Disclaimer: This information is for general reference. Code wording and instructions vary by model. Always follow the service manual for your exact unit.

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