American Standard AUH1B080A9H31A Error Code 5 Flashes: Flame Sensed When No Flame Should Be Present
What Does Code 5 Flashes Mean?
Code 5 (5 Flashes) on the American Standard AUH1B080A9H31A means the IFC board is sensing a flame signal while the gas valve is closed and no combustion should be taking place. This is treated as a safety-critical condition because the board cannot determine whether the signal is from a real flame or an electrical fault.
The most likely cause is a short circuit in the flame sensor wiring. The flame sensor operates by detecting a microamp-level current that flows through ionized combustion gases. If the sensor wire is damaged, grounded against the furnace chassis, or has deteriorated insulation, a false signal can reach the board. Moisture accumulation inside the furnace cabinet can also create a conductive path that mimics a flame signal.
Although less common, this code can also indicate a stuck-open gas valve that is allowing gas to flow to the burners when it should not. If you smell gas, leave the building immediately and call your gas utility's emergency line. Otherwise, turn off power to the furnace at the breaker and close the gas shutoff valve, then call an HVAC technician for professional diagnosis.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Short in flame sensor wiring | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Immediately — turn off the furnace and gas supply and have a technician inspect for wiring faults or gas valve issues
- If you smell gas, leave the building and call your gas utility emergency line before calling an HVAC technician
✓ Verified against manufacturer service manual — March 2026