American Standard AUD1B080A9H31A 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 AUD1B080A9H31A means the IFC board is detecting a flame signal even though the gas valve is closed and no combustion should be occurring. This is a safety-critical condition because it could indicate either a false electrical signal or, in rare cases, an actual unwanted flame from a stuck-open gas valve.
The most common cause is a short circuit in the flame sensor wiring. The flame sensor detects combustion by measuring a tiny microamp current that flows through the ionized gases in a flame. If the sensor wire is damaged, its insulation is compromised, or it contacts a grounded surface, the board can receive a false flame signal. Moisture inside the furnace cabinet can also cause this if it creates a conductive path.
In rare but more serious cases, this code can indicate a gas valve that is leaking or stuck in the open position, allowing gas to flow to the burners when it should not. For this reason, this code should always be treated as an urgent issue. Turn off the furnace at the circuit breaker and the gas supply at the manual shutoff valve, then call a qualified HVAC technician for diagnosis.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Short in flame sensor wiring | Most common | ✗ Call a pro → |
| Faulty control board | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Immediately — this code may indicate a gas valve leak or wiring fault that poses a safety risk
- Turn off the furnace and gas supply and have a technician inspect before operating again
✓ Verified against manufacturer service manual — March 2026