Trane XR90 Furnace Error Codes — What They Mean
The Trane XR90 is a single-stage 90% AFUE gas furnace with a PSC (permanent split capacitor) blower motor. It is one of Trane’s long-running mid-efficiency residential furnaces designed for reliability and straightforward service. The XR90 uses a control board with a status LED that reports fault codes via flash sequences. The board also includes a fault history LED window on some revisions that displays the last five fault codes as sticky memory.
Trane XR90 LED Flash Code Reference
| Flash Sequence | Fault |
|---|---|
| 1 flash | Normal — standby |
| 2 flashes | Pressure switch stuck open |
| 3 flashes | Pressure switch stuck closed |
| 4 flashes | Open limit device |
| 5 flashes | Flame sensed without gas valve call |
| 6 flashes | 115V power reversed — hot and neutral swapped |
| 7 flashes | Gas valve stuck open |
| 8 flashes | Ignition failure — exceeded retry limit |
| 9 flashes | Inducer motor fault |
| Rapid flash | Low voltage — check transformer |
| Continuous | Normal — blower running in cooling or fan mode |
Common Causes by Code
- 2 flashes — Pressure switch open — Blocked condensate drain line (the XR90 is a 90% unit with a condensate system), cracked pressure switch tubing, or failed inducer motor not creating sufficient draft. Check the condensate trap for blockage first — this is the most common cause on XR90s over 5 years old.
- 3 flashes — Pressure switch stuck closed — A pressure switch that closes before the inducer starts indicates a failed switch or a stuck switch from condensate in the switch. Disconnect the tubing from the pressure switch and blow it out.
- 4 flashes — Open limit — Airflow restriction causing heat exchanger overtemperature. Replace the air filter. Check for closed supply registers or a blocked return air path.
- 5 flashes — Flame without call — The flame sensor is detecting signal when the gas valve is off. This indicates a shorted or contaminated flame sensor creating a leakage current, or a failed gas valve that isn’t fully closing.
- 8 flashes — Ignition failure — The XR90 uses a hot surface igniter. Confirm gas supply is on, igniter glows red-orange (not dim yellow), and gas valve opens on ignition call (listen for the click of the valve solenoid).
- 9 flashes — Inducer fault — Inducer motor failed or speed too low. Check inducer capacitor (usually 5–7.5 µF) with a capacitor meter. A seized bearing is the other common cause — spin by hand with power off.
Step-by-Step Fix
- Count the LED flashes — The XR90 LED flashes a code, pauses, then repeats. Count the flashes in one cycle (from pause to pause). The code is the flash count.
- For 2 flashes (pressure switch open) — Check the condensate drain trap. On the XR90, the trap is usually a U-shaped PVC assembly under the secondary heat exchanger. Remove and flush with water. Also check the condensate hose from the secondary heat exchanger to the trap for kinks.
- For 4 flashes (limit) — Replace the filter immediately. If filters were just changed, check for a blocked or partially collapsed return air duct. Measure blower wheel RPM if possible — a failing PSC capacitor drops blower speed and reduces airflow.
- For 8 flashes (ignition failure) — Observe the ignition sequence: inducer starts (verify), igniter heats (glow visible through sight glass), gas valve opens, flame appears. If the flame lights then goes out within 5 seconds, the flame sensor needs cleaning.
- For 9 flashes (inducer) — Measure supply voltage to the inducer motor (115VAC). Check the capacitor. If voltage is present, capacitor is good, and the motor won’t spin, the motor windings have failed.
Parts Often Needed
| Part | Notes |
|---|---|
| Hot surface igniter | Norton 601, silicon carbide; fragile — don’t touch the ceramic |
| Flame sensor | Rod-type; clean with steel wool before replacing |
| Inducer motor capacitor | 5 or 7.5 µF; measure before replacing motor |
| Pressure switch | Two switches on some XR90 versions (high and low) |
| High-limit switch | L200°F on most XR90 configurations |
| Blower capacitor | PSC blower motor; dedicated capacitor |
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.
When to Call a Pro
The XR90 heat exchanger is a clamshell design that can crack at the secondary (condensate-side) section. If you smell combustion gases in the conditioned air, suspect a cracked heat exchanger — this is a safety issue requiring professional inspection and likely furnace replacement. Do not operate a furnace with a suspected cracked heat exchanger.