American Standard AUH1B080A9H31A Error Code 8 Flashes: Low Flame Sense Signal
What Does Code 8 Flashes Mean?
Code 8 (8 Flashes) on the White-Rodgers 50A65 Integrated Furnace Control (IFC) means the flame sensor is detecting a flame, but the signal it sends back is below the minimum the board wants to see. The flame sensor is a thin metal rod that sits in the burner flame and passes a tiny microamp current to prove the flame is present. A weak signal is the board's early warning that flame proof is becoming marginal.
On this single-stage furnace the cause is almost always a fouled sensor rod. Each heating cycle leaves a film of oxidation and carbon on the rod, and that film insulates it and cuts the current it can conduct. Because the furnace only has one firing rate, the rod sees the same flame every cycle and gradually accumulates buildup until the signal crosses the board's low threshold. Cleaning the rod restores the current.
It matters that you catch this at the 8-flash stage: if the signal keeps degrading until the board can no longer prove flame at all, ignition attempts start failing and the furnace can end in a 2-flash lockout. The 8-flash is also the opposite condition to the 5-flash code, where the board sees flame signal when there should be none. Cleaning the sensor is a homeowner-safe task; if the code returns quickly after a proper cleaning, the rod may be cracked or the sensing circuit may have another fault that a technician should evaluate.
What You'll Notice
- The diagnostic LED shows a repeating group of 8 flashes while the furnace still runs.
- The furnace may occasionally shut down mid-cycle as the marginal flame signal drops out.
- The flame sensor rod, when inspected, is coated with a dark or whitish film rather than being clean metal.
- Heating may become intermittent — working one cycle and failing the next — as the signal hovers near the threshold.
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 Set the furnace breaker (or the furnace power switch) to OFF, and turn the gas supply valve to OFF (handle perpendicular to the pipe). Wait a few minutes before working near the burners so they are not hot. If you smell gas at any point, leave your home immediately and call your gas company from outside.
- Open the burner compartment access panel Remove the furnace's lower access panel to reach the burner area. It lifts out or is held by a few screws or clips. Use a flashlight to see inside.
- Locate and remove the flame sensor The flame sensor is a thin metal rod, usually bent at an angle, mounted near the burners with a single wire and one mounting screw — typically on the opposite end of the burners from the igniter. Note its orientation, remove the mounting screw, disconnect the wire, and gently withdraw the rod.
- Clean the sensor rod Gently clean the flame sensor rod with a Scotch-Brite pad until the metal is dull-bright. American Standard's guide lists fine steel wool as the cleaning material, but many HVAC technicians prefer a Scotch-Brite pad because it leaves no abrasive residue on the rod. Do not clean or scratch the white porcelain base, and take care not to bend the rod. Wipe the rod with a clean dry cloth when finished.
- Reinstall the flame sensor Slide the rod back into its original position and orientation, secure the mounting screw, and firmly reconnect the wire. Make sure the rod will sit in the burner flame path but is not touching any grounded metal surface.
- Restore gas and power, then test Reinstall the access panel, turn the gas valve back to ON (handle parallel to the pipe), and set the breaker/switch back to ON. Set the thermostat to call for heat and watch the furnace go through ignition.
When to Call a Professional
Contact a licensed HVAC technician if:
- The 8-flash code returns soon after a proper flame-sensor cleaning
- The sensor rod appears cracked, pitted, or physically damaged rather than just dirty
- The furnace lights and then repeatedly shuts down within a few seconds even after cleaning
- You are not comfortable working inside the burner compartment
Frequently Asked Questions
How do I clean the flame sensor on my American Standard AUH1B080A9H31A?
With the power and gas off, remove the single-screw sensor rod near the burners and gently clean it with a Scotch-Brite pad until the metal is dull-bright, avoiding the white porcelain base, then reinstall it. This resolves most 8-flash low-signal codes.
How often does the flame sensor need cleaning?
It varies by home conditions and run time, so there is no fixed interval, but a once-a-year cleaning as part of routine maintenance keeps the signal strong on this single-stage furnace. Clean it sooner if the 8-flash code appears.
The code came back right after I cleaned the sensor — what does that mean?
If a proper cleaning does not hold, the rod may be cracked or the sensing circuit may have another fault, such as a grounded wire. At that point a technician should test and likely replace the sensor.
Sources
✓ Verified against manufacturer service manual — March 2026