Trane TUD1B080A9H31B Error Code 5 Flashes: Flame Sensed When No Flame Should Be Present
What Does Code 5 Flashes Mean?
A 5-flash code on the Trane TUD1B080A9H31B means the flame sensor is sending a flame signal to the control board while the gas valve is de-energized and no flame should exist. The furnace treats this as a safety-critical condition and will not attempt to operate.
This code most commonly results from a short circuit in the flame sensor wiring. If the flame sensor wire contacts the furnace chassis or another grounded surface, it can create a false flame signal that the control board interprets as an actual flame. A malfunctioning control board can also misread the flame sensor input. In rare but serious cases, a gas valve that is stuck partially open could allow gas to reach the burners and actually produce a flame when none is expected.
If you smell gas, leave your home immediately and call your gas utility company from outside. Otherwise, turn off the furnace at the circuit breaker and call a qualified HVAC technician. Do not attempt to diagnose this condition yourself, as it involves potential gas safety hazards.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Short in flame sensor wiring | Most common | ✗ Call a pro → |
| Faulty control board | Common | ✗ Call a pro → |
| Stuck-open gas valve | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Immediately when this code appears — potential gas valve or flame sensor wiring issue that poses a safety risk
✓ Verified against manufacturer service manual — March 2026