Trane TUH1B080A9H31A 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 TUH1B080A9H31A means the flame sensor is reporting flame presence while the gas valve is de-energized. Under normal operation, no flame should exist when the gas valve is closed, so this reading indicates a malfunction in the sensing circuit or, more seriously, an actual gas leak through a stuck valve.
A short circuit in the flame sensor wiring is the most likely cause. If the sensor wire's insulation has degraded from heat exposure and the bare wire touches the furnace chassis, it generates a false flame signal. A failing control board that misinterprets the flame sensor input can also produce this code. Although less common, a gas valve with a stuck-open internal mechanism would be the most dangerous cause, as it means gas is actually flowing to the burners when it should not be.
If you smell gas at any point, leave your home immediately and call your gas utility from outside. If there is no gas smell, shut off the furnace at the circuit breaker and contact a qualified HVAC technician for diagnosis. Do not attempt to troubleshoot this yourself.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Short in flame sensor wiring | Most common | ✗ Call a pro → |
| Faulty control board | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Immediately — this code indicates a potential gas safety hazard requiring professional inspection of the gas valve and flame sensor circuit
✓ Verified against manufacturer service manual — March 2026