Trane Furnace Error Code 8 Flash

An 8 Flash code on a Trane furnace means the flame sense current has dropped below 1 microamp DC. This is below the normal operating threshold, but the signal is still sufficient for the furnace to continue running. It is a warning condition indicating the flame sensing circuit is degraded and needs attention before more serious faults develop.

The furnace is still operating when this code appears, so it is not an immediate safety emergency. However, a degraded flame sense signal means the control board's ability to confirm that the burner flame is present is compromised. Allowing this condition to persist increases the risk of the furnace failing to detect a loss of flame, which is a safety-critical function. Addressing the code promptly is strongly recommended.

Resetting the furnace may temporarily clear the displayed fault, but the underlying cause of the low flame sense signal will remain. If the sensor rod is dirty, misaligned, or the wiring is faulty, the code will return once the furnace goes through another heating cycle. A reset should only be used after the root cause has been identified and corrected.

In many cases, yes. The most common fix is cleaning the flame sensor rod, which a knowledgeable DIYer can do by shutting off power, removing the sensor, and gently cleaning the rod with fine steel wool or emery cloth. You should also check that the sensor is correctly positioned in the flame and that all wiring connections are tight and undamaged. If cleaning and inspection do not resolve the fault, testing with a voltmeter on the DC microamp scale while the burner is running will confirm whether the signal has improved.

If the fix is simply cleaning the flame sensor rod, the cost is minimal, typically just your time or a basic service call fee ranging from $75 to $150 depending on your area. If the sensor rod needs replacement, parts are inexpensive, generally in the $15 to $40 range, with labor bringing the total to roughly $100 to $200. If wiring or control board issues are involved, costs will be higher.