How to read the Trane furnace status light
Applies to: Trane and American Standard gas furnaces
What this error means
On most Trane/American Standard furnace boards the diagnostic LED is RED, and the 'normal' states confuse everyone: SLOW flashing = normal standby (no call for heat), FAST flashing = normal operation with a call for heat. Counted groups of flashes (2, 3, 4, 5…) are fault codes. Steady ON = replace the board; steady OFF = no power. (Some board families — including Trane's light-commercial ReliaTel and certain models — use a green LED with similar logic, but 'flashing means broken' is the myth to unlearn: flashing is usually normal.)
Symptoms
- Blinking red light on the control board
- Uncertainty about whether blinking = fault
Try this first (safe DIY steps)
- Slow or fast steady blinking with heat working = normal, leave it alone
- Counted groups with pauses = a code; count it, write it down, look it up (see our 2/3/4/5-flash guides)
- Steady on or completely off = board or power problem; check the furnace switch and breaker first
Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.
When to call a technician
Steady-on LED (board replacement, $400–$700 installed) or any code involving gas safety.