Trane Furnace Error Code Green OFF / Red Flashing (during ignition try)

This error means the ignition control module attempted to light the burner but could not detect a valid flame signal during the ignition trial. The Red LED flashes for 5 seconds at the start of each retry attempt alongside a flashing Green LED. The module will try up to three times before locking out. Common causes include a dirty flame sensor, a failed igniter, or an insufficient gas supply.

The furnace will not continue operating unsafely because the control module locks out after three failed ignition trials, cutting off any further attempts. There is no active flame or gas flow once lockout occurs. However, you should not repeatedly reset the unit without investigating the cause, as persistent ignition failures can point to a gas supply or component issue that warrants professional attention.

Repair costs vary depending on which component has failed. Flame sensor cleaning is inexpensive if done as part of a routine service call, generally in the range of $80 to $150 for a diagnostic visit. A replacement hot surface igniter typically adds $100 to $250 in parts and labor. A gas valve replacement is more involved and can range from $300 to $600 or more depending on the part and labor rates in your area.

Some steps are within reach for a knowledgeable DIYer. Cleaning the flame sensor rod with fine steel wool or emery cloth is a straightforward task that often resolves the fault. Verifying that the manual gas shutoff valve is fully open and that gas pressure is available is also safe to check. However, testing or replacing the gas valve or ignition control module involves working around gas lines and line-voltage components, which is best handled by a licensed HVAC technician.

Resetting the furnace will clear the lockout and allow the module to attempt another ignition sequence. However, if the underlying problem such as a dirty flame sensor, failed igniter, or gas supply issue is not resolved, the unit will simply run through the three trials again and re-enter lockout. A reset is useful for confirming the fault is repeatable, but it is not a repair.