Trane and American Standard furnaces, built by the same company, use a red LED on the control board that flashes in groups to report faults. The most common codes are 2 flashes (lockout after failed ignition retries), 3 flashes (pressure switch error) and 4 flashes (open limit switch). On many models the light also blinks slowly or quickly during normal operation, which isn’t a fault.
Before you start
- Record the code before turning off power. Some boards clear it when power is cut.
- Confirm with the label inside your furnace’s blower door. Codes can differ between control boards and model years.
- Reset only once or twice. Turn off power for 30 seconds and restore it. A code that comes back means a real problem.
- Safety: if you smell gas, leave the home and call your gas utility or 911 from outside. Never bypass a safety switch.
Trane and American Standard LED codes
| LED pattern | Meaning | What to check |
|---|---|---|
| Off | No power to the board | Power switch, breaker, blower door switch, fuse |
| Slow flash | Normal: no call for heat | — |
| Quick flash | Normal: furnace running or about to run | — |
| Solid on (not flashing) | Control board or wiring problem | Technician |
| 2 flashes | Lockout after too many ignition retries | Gas supply, flame sensor, igniter |
| 3 flashes | Pressure switch error | Blocked vent or intake, clogged drain, hose, inducer |
| 4 flashes | Open limit switch | Dirty filter, closed vents, blower |
| 5 flashes | Flame sensed with the gas valve off | Gas valve or control board; technician |
| 6 flashes | Line voltage polarity reversed | Wiring; technician |
| 7 flashes | Gas valve circuit problem | Gas valve or control board; technician |
| 8 flashes | Low flame signal | Flame sensor, grounding, flame quality |
| 9 flashes | Igniter problem | Igniter or control board |
Based on the common Trane and American Standard control board chart (reference). Older boards and communicating models (such as those paired with ComfortLink or Link thermostats) can use different codes or show them on the thermostat. Check the label inside your furnace door.
What to do for the most common codes
2 flashes: lockout
The furnace tried to light several times without proving flame. Most boards reset after about an hour, or you can cycle power once.
- Check that the gas valve is open and other gas appliances work.
- Clean the flame sensor: how to clean a furnace flame sensor.
- If the igniter doesn’t glow: furnace ignitor not glowing.
3 flashes: pressure switch error
- Clear snow, ice, leaves or nests from the outdoor PVC vent and intake pipes on high-efficiency models.
- Check the condensate drain and trap, and look for water or cracks in the pressure switch hose.
- If those are fine, the inducer or the switch may be failing; call a technician.
4 flashes: open limit switch
- Replace the air filter: how often to change your air filter.
- Open all supply vents and clear return grilles.
- If it repeats, have a technician check the blower motor and limit switch.
8 flashes: low flame signal
Clean the flame sensor and make sure the furnace is properly grounded. If the burner flame looks yellow or lazy, call a technician.
When to call a technician
Call a licensed HVAC technician if the same code returns after one reset, or right away for rollout switch, flame-sensed-with-gas-valve-off, gas valve, polarity or control board codes. Give the technician the code, the furnace model number and when the problem started; it speeds up the repair.
For a complete troubleshooting sequence, see Furnace Not Turning On: 11 Causes and Fixes. For other brands, see our furnace blinking light codes guide.
For a deeper look at the two most common faults behind these codes, see furnace pressure switch problems and furnace high limit switch tripping.
Disclaimer: this guide is for general information only and summarizes common Trane and American Standard control board codes. Codes vary by model and board; always confirm with the label inside your furnace or the manufacturer’s literature. Gas furnaces involve gas, combustion and high voltage. Contact a licensed HVAC professional for repairs.