American Standard AUH1B080A9H31A Error Code 8 Flashes: Low Flame Sense Signal
What Does Code 8 Flashes Mean?
An 8-flash code on your American Standard AUH1B080A9H31A furnace indicates that the flame sensor is detecting a flame, but the electrical signal it produces is below the minimum threshold required by the IFC control board. The flame sensor is a small metal rod that sits in the burner flame and generates a tiny electrical current (measured in microamps) to prove that a flame is present.
Over time, the flame sensor rod develops a layer of oxidation and carbon buildup from exposure to the burner flame. This coating acts as an insulator, reducing the electrical current the sensor can produce. When the current drops below the board's minimum threshold, the furnace may continue to run but displays this warning code, or it may begin experiencing intermittent shutdowns as the signal becomes too weak.
Cleaning the flame sensor rod is one of the most common and straightforward furnace maintenance tasks. Many professionals prefer cleaning the sensor rod with a Scotch-Brite pad as it leaves no abrasive residue. This fix resolves the issue in the vast majority of cases.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty or oxidized flame sensor rod | Most common | ✓ DIY fix → |
| Cracked or damaged flame sensor | Uncommon | ✗ Call a pro → |
How to Fix It: Clean the Flame Sensor
What You'll Need
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Locate the circuit breaker for your furnace in your electrical panel and flip it to OFF. Also turn the gas supply valve to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave your home immediately and call your gas company from outside.
- Remove the furnace access panel Remove the lower front access panel of the furnace to access the burner compartment. This panel typically lifts up and pulls out, or may be secured with screws.
- Locate the flame sensor The flame sensor is a thin metal rod (usually bent at an angle) mounted near the burners, typically on the opposite end from the igniter. It has a single wire connected to it and is held in place by one mounting screw.
- Remove the flame sensor Disconnect the wire from the flame sensor and remove the single mounting screw (usually 1/4-inch). Carefully pull the flame sensor out of its bracket.
- Clean the sensor rod Gently rub the metal rod portion of the flame sensor with fine a Scotch-Brite pad until the surface appears clean and shiny. Do not use steel wool or anything abrasive that could damage the rod. Wipe the rod with a clean, dry cloth after cleaning to remove any residue.
- Reinstall the flame sensor Reinsert the flame sensor into its bracket, replace the mounting screw, and reconnect the wire. Make sure the sensor rod is positioned so it will sit in the burner flame when the furnace operates.
- Restore power and gas supply Replace the access panel, turn the gas supply valve back to ON (parallel to the pipe), and flip the circuit breaker back to ON.
When to Call a Professional
Contact a licensed HVAC technician if:
- The 8-flash code returns after cleaning the flame sensor
- The flame sensor rod appears cracked, pitted, or damaged
- The furnace ignites but shuts down within a few seconds repeatedly
- You are not comfortable working near the burner area of the furnace
- The flame appears yellow or uneven instead of a steady blue
✓ Verified against manufacturer service manual — March 2026