American Standard AUD1B080A9H31A Error Code 8 Flashes: Low Flame Sense Signal

What Does Code 8 Flashes Mean?

An 8-flash code on the White-Rodgers 50A65 Integrated Furnace Control (IFC) means the flame sensor is detecting a flame, but the electrical signal it produces has fallen below the board's minimum threshold. The sensor is a thin metal rod that sits in the burner flame and passes a tiny microamp current to prove flame is present. When that current gets too weak, the board flags this warning.

The usual cause is a fouled sensor rod. Over many heating cycles the rod develops a film of oxidation and carbon that insulates it and chokes off the current the board can read. This is the early-warning side of the flame-sensing story on this furnace: left unaddressed, the signal can drop far enough that ignition attempts are scored as failures and the board escalates to a 2-flash system lockout. It is the opposite condition from the 5-flash code, where the board reads flame when the valve is closed and none should exist.

Cleaning the flame sensor is one of the most common, lowest-risk furnace maintenance tasks and typically restores the signal. If the code returns soon after a proper cleaning, the rod may be cracked or the porcelain insulator damaged, and the sensor should be replaced by a technician.

What You'll Notice

• The diagnostic LED blinks eight times, pauses, and repeats, sometimes while the furnace is still running.
• The furnace may light and heat normally at first but occasionally drops the flame and shuts down mid-cycle.
• You may notice the furnace short-cycling, or the burners lighting and going out shortly after.
• The flame sensor rod, when inspected, looks dark, sooty, or oxidized rather than clean metal.

Common Causes

How This Is Diagnosed

Because a fouled rod is by far the most common cause, cleaning it is both the first diagnostic step and the fix. If a proper cleaning does not restore the signal, a technician measures the flame current in microamps against the board's specification, inspects the rod and porcelain for cracks, and checks the sensor wiring for a partial short to ground before replacing the sensor. A signal that stays weak with a clean, undamaged rod points to wiring or the board.

How to Fix It: Clean the Flame Sensor

What You'll Need

• Scotch-Brite pad
• 1/4-inch nut driver or hex-head screwdriver
• Clean dry cloth
• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Flip the furnace circuit breaker to OFF and turn the gas supply valve to OFF (perpendicular to the pipe) before opening anything. If you smell gas at any point, leave your home immediately and call your gas company from outside.
2. Open the burner-compartment access panel Remove the furnace access panel that exposes the burners. It typically lifts out or is held by a few screws. Set it aside where the door-interlock switch will not be tripped accidentally.
3. Locate and remove the flame sensor The flame sensor is a thin metal rod, often bent at an angle, mounted near the burners on the opposite end from the igniter, with a single wire and one mounting screw. Note its orientation, disconnect the wire, remove the screw, and carefully withdraw the sensor.
4. 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.
5. Reinstall the flame sensor Slide the sensor back into its original position so the rod will sit in the burner flame, secure the mounting screw, and firmly reconnect the wire.
6. Restore gas and power, then test Replace the access panel, turn the gas valve back to ON (parallel to the pipe), and flip the breaker to ON. Set the thermostat to call for heat and watch the furnace run its ignition sequence.

When to Call a Professional

Contact a licensed HVAC technician if:

• The 8-flash code returns soon after a careful cleaning of the flame sensor.
• The sensor rod appears cracked, pitted, or the white porcelain base is chipped.
• The furnace lights and then drops out after a few seconds, or has begun locking out with a 2-flash code.
• The burner flame looks yellow or lazy rather than a steady blue.

✓ Verified against manufacturer service manual — March 2026