Trane Furnace: 8 Flashes
Code 8 Flashes: Low flame sense signal
WarningShown as: 8 flashes, pause, repeat
Low flame sense signal. The furnace is running, but the flame current the control reads is weak, so it is warning that flame proving is marginal.
Manual wording: “8 Flashes --- Low flame sense signal”
Documented for: *UH1 / *DH1 condensing furnaces (XR 95 family) and other Trane furnaces using the LED-only integrated furnace control
Likely causes, most common first
- Low flame sense signal
What you can safely check yourself
- Note whether the furnace is still heating; this code usually appears while the furnace is still running
When to call a technician
Schedule service. A weak flame signal usually means the flame sensor needs cleaning or the burner flame is not right, and if it drops further the furnace will lock out. Cleaning the flame sensor means working in the burner compartment, so leave it to a technician.
A Trane furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installer's Guide - Upflow/Horizontal, Downflow/Horizontal, Gas-Fired, Direct Vent Condensing Furnaces (18-CD29D1-14-EN) (Trane, *UH1B/*UH1C/*UH1D upflow and *DH1B/*DH1C/*DH1D downflow condensing gas furnaces (XR 95 family; first letter A or T)) · checked 2026-08-25