Trane Furnace Code E4.1
Safety fault
The reverse air-flow limit switch has opened, meaning air is moving through the furnace the wrong way or a downflow/horizontal airflow fault has been sensed.
Manual wording: “Open reverse air-flow limit switch”
Documented for: S8V2 two-stage induced draft furnaces (FNR-SVX003A control revision)
Likely causes, most common first
- Open reverse air-flow limit switch
- Blower rotating backwards or wired incorrectly
- Airflow problem specific to the furnace's installed orientation
What you can safely check yourself
- Check that the furnace blower door is fully closed and latched
- Check the air filter and replace it if dirty
When to call a technician
Call a technician. A reverse airflow trip means combustion products could be pushed the wrong way and it needs to be diagnosed before the furnace runs again.
A Trane furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation, Operation, and Maintenance - Link Communicating or 24 Volt Gas-Fired 2 Stage Induced Draft Furnaces with Variable Speed Motor (FNR-SVX003A-EN) (Trane, S8V2A040M3PCB through S8V2D120M5PCB two-stage 80% induced draft furnaces (communicating or 24V)) · checked 2026-08-25