Err.126.00
Equipment Change Alert — equipment reporting does not match equipment originally discovered; enabled device is offline or not reporting on bus
This code typically points to
- Communicating device not reporting on bus
- Power flicker to device (equipment stopped reporting)
- ABCD bus wiring fault
- Failed communicating board on a discovered device
- Outdoor unit not reporting
Next checks to confirm
- Check wall-control Summary Table to identify which device is offline
- If outdoor unit offline and heat pump not running (system falls back to furnace/electric heat): verify outdoor power, comm wiring, and board state
- Cycle/restore reporting status of missing device
- If device was removed intentionally, set to Disabled in Summary Table
Escalation
On heat-pump systems: compressor operation may be lost, system may fall back to furnace or electric heat only
Reset behavior
Clears when missing/offline device returns to reporting status on the bus. No unique reset button — alert self-clears on device reconnection.
Urgent
Fix now