Lennox EL296UHV Error Code E 105: Device Communication Problem
What Does Code E 105 Mean?
Error code E105 on the Lennox EL296UHV indicates a device communication problem on the RS Bus. The control board is unable to communicate with other connected devices such as the thermostat or outdoor unit, and has detected numerous message errors on the communication bus.
In most cases, communication errors on the RS Bus are caused by electrical noise interference. High-voltage power wiring running too close to the low-voltage communication wires can induce noise that corrupts data signals. This is especially common if the communication wires were routed alongside 120V or 240V power cables during installation.
Loose or mis-wired connections between the thermostat, indoor unit, and outdoor unit are the other primary cause. A connection that is not fully seated or a wire that has worked loose from a terminal can create intermittent communication failures. The fault clears automatically once stable communication is restored between all system devices.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Electrical noise interference with communication bus | Most common | ✗ Call a pro → |
| Loose or mis-wired connections between thermostat and units | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The furnace repeatedly shows E105 and loses communication with the thermostat
- The system works intermittently with communication dropping in and out
- You recently had electrical work done in the home
✓ Verified against manufacturer service manual — March 2026