Lennox
General Equipment Non-Response
Thermostat shows 'Equipment not responding' or similar message without a specific numeric code.
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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
Loss of communication on Lennox ABCD bus, Indoor or outdoor unit control board failure, Miswired or reversed ABCD conductors, Tripped breaker to indoor or outdoor unit
How to Fix / Troubleshooting
Safety warning: Turn off power to both indoor and outdoor units before opening panels or touching wiring.
- 1. Check power to all equipment:
- Verify breakers for furnace/air handler and outdoor unit are ON.
- 2. Inspect ABCD wiring:
- Ensure A-A, B-B, C-C, D-D are correctly matched and firmly connected at thermostat, indoor, and outdoor units.
- 3. Power cycle system:
- Turn off all HVAC breakers for 5 minutes, then restore power and allow devices to re-sync.
- 4. If message persists:
- A Lennox technician should check control boards and communication circuits.
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Repair Difficulty
Hard
4/5
Required Part
Lennox Furnace/Air Handler Control Board
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