Lennox Furnace Code E105
Warning
Device communication problem. The furnace control sees no other devices on the communication bus, so the thermostat, furnace and outdoor unit are not talking to each other.
Manual wording: “Device communication problem - No other devices on BUS (Communication system).”
Documented for: SLP98UHV series and other Lennox communicating furnaces with a seven-segment diagnostic display
Likely causes, most common first
- Miswired or loose communication bus connections between thermostat, furnace and outdoor unit
- A high voltage source of electrical noise near the system, such as a welder
- Broken or damaged thermostat wiring
What you can safely check yourself
- Check that the thermostat display is on and, if it is battery powered, that the batteries are good
- Check that the furnace door is fully seated and the furnace power switch and breaker are on
- Turn power to the furnace off for 30 seconds and back on once
When to call a technician
Tracing communication bus wiring between the thermostat, furnace and outdoor unit is a technician job.
A Lennox furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- SLP98UHV Service Literature (Corp. 1029-L7), Table 14 - LED 7 Segment Status / Error Code and Integrated Control Diagnostic Codes (Lennox Industries Inc., SLP98UHV series variable-capacity communicating gas furnace (66,000-132,000 Btuh)) · checked 2026-08-25