Trane TUD1B080A9H31B Error Code 6 Flashes: 115V AC Power Reversed, Poor Grounding, or System Voltage Too Low
What Does Code 6 Flashes Mean?
A 6-flash code on the Trane TUD1B080A9H31B indicates an electrical supply problem. The control board has detected that the 115VAC hot and neutral wires may be reversed, the furnace grounding is inadequate, or the incoming voltage is below acceptable levels. Any of these conditions interfere with the flame sensing circuit, which relies on proper polarity and grounding to detect the burner flame accurately.
Reversed polarity is the most common cause and typically originates from incorrect wiring during installation or a recent electrical service change. Poor grounding can develop over time as connections corrode or loosen. Low system voltage is less common but can occur if the furnace shares a circuit with high-draw appliances or if the utility voltage drops during peak demand.
The furnace may still operate intermittently with this condition, but flame detection will be unreliable, leading to nuisance shutdowns. A qualified HVAC technician or electrician needs to check the wiring polarity at the furnace junction box, verify the ground connection integrity, and measure the incoming voltage to identify and correct the specific issue.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- When this code appears — electrical wiring and grounding corrections require a licensed technician or electrician
✓ Verified against manufacturer service manual — March 2026