Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Trane Furnace Error Codes — Quick Reference
Trane gas furnaces communicate faults through a flashing green or red LED on the control board. Remove the lower access panel and count the blink sequence — the number repeats continuously until the fault clears. Trane also makes American Standard furnaces; the control boards and codes are identical. Newer Trane communicating systems (ComfortLink II) display alphanumeric codes on the thermostat.
| Code | Meaning | Quick Fix |
|---|---|---|
| 1 flash | System lockout | Reset power; check igniter and gas |
| 2 flashes | Pressure switch fault | Check inducer, hose, condensate drain |
| 3 flashes | High-limit or roll-out open | Replace filter; check airflow |
| 4 flashes | Ignition failure | Check igniter, gas valve, flame sensor |
| 5 flashes | Flame sense without call | Possible gas valve leak |
| 6 flashes | 115V power fault / reversed polarity | Check wiring polarity |
| 7 flashes | Gas valve fault | Gas valve or board issue |
| 8 flashes | Low flame signal | Clean flame sensor |
| 9 flashes | Igniter fault | Replace igniter |
| 126 | Communication loss | Check thermostat wiring |
| 79 | Airflow fault | Verify filter and duct static pressure |
| ER | Communicating system error | Check all ComfortLink wiring |
Technician Tips
Trane furnaces typically flash error codes through the LED on the integrated furnace control (IFC) board. Code 11 (no previous code) is the startup default — if you see this with a no-heat call, check for power at the IFC. Code 12 means blower on after power-up — normal after a reset. Code 13 means limit switch fault — this is often a dirty filter or restricted return. Code 14 means ignition failure — check gas pressure before condemning the igniter. Trane uses silicon nitride igniters that last longer than standard carbides but are more fragile during handling.
Estimated repair time: Most Trane ignition faults take 30-45 minutes to diagnose and fix. Limit switch and blower motor issues run 1-2 hours.
Need Replacement Parts?
Before ordering, match the furnace part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Most Common Codes
2 Flashes: Pressure Switch Fault
The induced draft blower started but failed to prove suction. On Trane XR90 and XR95 models, a plugged secondary heat exchanger is the #1 cause after condensate drain blockage. Check the clear plastic condensate trap for standing water, inspect the rubber pressure switch hose, and verify the inducer wheel turns freely.
3 Flashes: High Limit or Roll-Out Open
High-limit trips most often from a dirty air filter or a failed blower motor. On Trane XB80 and XR80 models, check the blower capacitor — a weak capacitor causes the motor to run slowly and trip the limit. Roll-out trips require investigation of the heat exchanger for cracks before resetting.
4 Flashes: Ignition Failure
The burner failed to light after three attempts. Verify the gas supply shutoff valve is fully open. Inspect the silicon nitride igniter — resistance should read 40–90 ohms when cold. A reading of OL (open circuit) means the igniter has cracked and needs replacement.
5 Flashes: Flame Sensed — No Call
Gas is burning when the thermostat hasn’t requested heat. This points to a leaking gas valve or a shorted flame sensor circuit. This is a safety fault — shut off gas supply immediately.
8 Flashes: Low Flame Signal
Burner lit but microamp signal is weak. Remove the flame sensor rod, clean with fine steel wool, and reinstall. Healthy signal is typically 1.5–6 µA. If cleaning doesn’t help, check the sensor position relative to the burner flame.
Code 126: Communication Loss
On ComfortLink II systems, this means the thermostat and furnace board have lost communication. Check the 2-wire communication bus between the thermostat and furnace. Loose terminals at either end are the most common cause.
When to Call a Pro
Roll-out switch trips (3 flashes) and flame-without-call faults (5 flashes) are safety events. Don’t reset and ignore these — have a technician inspect the heat exchanger and gas valve before returning the furnace to service.