Trane Furnace Error Code 5 Flash

A 5 Flash code on a Trane furnace means the control board has detected a flame signal when no flame should be present. This is called a flame detect fault and is a safety lockout condition. It most commonly points to a gas valve that is not fully closing, but it can also be caused by a faulty flame sensor or shorted wiring in the flame sense circuit.

Resetting the furnace by cutting power and restoring it may temporarily clear the fault, but the code will return if the underlying problem is not corrected. The control board will re-enter lockout as soon as it detects the abnormal flame signal again. A reset alone is not a fix and should only be used as part of a diagnostic process.

Repair costs vary depending on the failed component. A gas valve replacement typically runs in the range of $200 to $600 including parts and labor. A flame sensor is a much less expensive part, generally in the $20 to $80 range for the component, with labor added on top. Control board replacement is the most costly scenario, often ranging from $400 to $900 or more depending on the specific model.

Yes, this fault should be taken seriously. If the gas valve is leaking and sustaining an unintended flame, it represents a combustion safety risk. Turn off the gas supply to the furnace and disconnect electrical power before performing any inspection. Do not attempt to bypass or ignore this fault code.

Start by disconnecting power and shutting off the gas supply, then remove the gas valve to inspect the inlet gas screen for moisture or debris. If the screen is contaminated, clean or replace the valve. If the valve is intact, inspect the flame sensor ceramic for cracks and check the sensor wiring for shorts to ground. If all components test properly, the control board may need replacement.