HVACopedia

Lennox · Air handler

11 Missing device

High severity

What the control is telling you

The thermostat can no longer find a component that was installed during setup. S30/S40 thermostat alert code 11.

Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems

Likely causes

  • Device lost power or communication wiring
  • Device not Lennox communicating compatible
  • Device removed or failed

Test and repair steps

  1. Check every device's R, i+, i- and C wiring and that each device is Lennox communicating compatible.
  2. Cycle system power.
  3. Still there? Reconfigure. S30: go to Menu > Settings > Advanced Settings, open View Dealer Control Center, then pick Equipment > Reset All Equipment. The thermostat will find every Lennox communicating device again.
  4. S40 go to Menu > Settings > Advanced Settings, open View Service Support Center, then Equipment Setting > Reset and pick Reset HVAC Equipment.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.8. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.