Trane TUH1B080A9H31A Error Code 8 Flashes: Low Flame Sense Signal
What Does Code 8 Flashes Mean?
The 8-flash code on the Trane TUH1B080A9H31A indicates a low flame sense signal. The flame sensor is detecting the burner flame, but the signal strength is below the minimum threshold. This can cause the furnace to run briefly then shut down, or to cycle on and off repeatedly.
The flame sensor is a thin metal rod positioned in the burner flame. It works by conducting a tiny microamp-level electrical current through the flame. Over time, carbon deposits and oxidation build up on the rod, reducing the current it can conduct. When the signal weakens enough, the control board may shut off the gas because it cannot reliably confirm the flame is present.
Less common causes include poor electrical grounding that interferes with the flame sensing circuit. If cleaning the sensor does not resolve the issue, the grounding and wiring should be checked by a professional.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty flame sensor rod | Most common | ✗ Call a pro → |
| Poor grounding | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The 8-flash code returns after thoroughly cleaning the flame sensor
- The furnace shuts off within seconds of igniting even with a clean sensor
- The sensor rod is visibly cracked, bent, or corroded beyond cleaning
- You notice the flame color is yellow or orange instead of blue
- The furnace also displays other error codes
✓ Verified against manufacturer service manual — March 2026