E250
Lennox System Configuration Error

Thermostat displays E250 indicating configuration or equipment mismatch; system may not operate correctly.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Incorrect equipment type selected in Lennox thermostat installer setup, Wrong number of stages or heat pump configuration, Misidentified communicating vs. non-communicating system, Incompatible Lennox equipment connected

How to Fix / Troubleshooting

Safety warning: Do not change wiring with power on. Turn off power to the indoor unit before altering connections.

  • 1. Review installer setup:
    • Enter the installer or advanced setup menu on the Lennox thermostat.
    • Verify equipment type (furnace, air handler, heat pump), fuel type, and number of stages match the installed Lennox equipment.
  • 2. Check communicating vs. conventional wiring:
    • If using Lennox communicating equipment, ensure ABCD bus is used and conventional R/C/Y/W wires are not misused.
    • If using non-communicating equipment, ensure standard R/C/Y/W/O/B wiring is used and communicating mode is disabled.
  • 3. Correct any mismatches:
    • Adjust thermostat configuration to match the model numbers and capabilities of the Lennox furnace, air handler, and outdoor unit.
  • 4. If unsure:
    • Contact a Lennox dealer or technician to verify system design and configuration.
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Repair Difficulty

Medium 3/5
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