Trane and American Standard furnaces report faults through a flashing LED on the integrated furnace control (IFC), viewed through the blower door. Red flash counts of 2 through 10 identify the fault (10 appears on two-stage boards), a continuous red and green LED means the control itself has failed, and the blower motor is the cause in a small set of cases, mainly open limit (4 flashes) and communication faults (10 flashes on two-stage boards).
Key Takeaways
- Green LED slow flash is normal with no call for heat; green fast flash is normal with a call for heat present.
- Red LED flash counts are the fault codes. One flash every 20 seconds is normal operation.
- Blower-related codes: 4 flashes (open limit switch) and, on two-stage boards, 10 flashes (communication fault).
- Both LEDs continuous on means internal control failure; both continuous off means an open fuse.
- Meanings differ slightly between control revisions (codes 6, 9 and 10), so confirm against the legend on the blower door.
How to Read Trane and American Standard LED Codes
The legend below comes from Trane service installer's guides for IFC replacement kits (18-CH92D1, 18-CH93D1, 18-CH111D1 and 18-CH76D1). Count red flashes during a call for heat and leave power on while reading, because cutting power can clear the code being displayed.
| Red LED Flashes | Meaning | Blower Motor the Cause? |
|---|---|---|
| 1 (every 20 seconds) | Normal operation | No |
| 2 | System lockout, retries or recycles exceeded | Rarely |
| 3 | Pressure switch fault | No |
| 4 | Open limit switch | Yes, common |
| 5 | Flame sensed when none should be present | No |
| 6 | 115 V AC reversed or improper ground (igniter fault on some two-stage boards) | No |
| 7 | Gas valve circuit error | No |
| 8 | Low flame sense signal | No |
| 9 | Igniter relay fault (open inducer limit on some two-stage boards) | No |
| 10 | Communication fault (two-stage boards only) | Possible |
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Blower-Related Codes First
10 Flashes: Communication Fault
Trane lists 10 flashes as a communication fault on its two-stage control (18-CH76D1). Published summaries of Trane variable-speed service literature include the blower motor not responding on the serial motor wiring among the causes. In five minutes, confirm 120 V AC at the motor power connector, reseat the control harness at the motor and the board, and look for a pinched or chafed lead. If power and wiring are good and the motor does not answer, the motor or its module is the suspect. The blower motor not responding on the serial wiring is one of the listed causes, along with the control and wiring.
4 Flashes: Open Limit Switch
The limit opened because the heat exchanger got hot. Check the filter, closed registers and the blower wheel first. Then confirm the blower starts and reaches speed during the heating cycle. A weak, slow or stalled blower lets the limit trip, so the motor is a common cause. A limit that stays open after the furnace cools points to the switch or its wiring instead.
Quick Motor Check Before Replacing Anything
- Measure line voltage at the motor power connector.
- Measure the control signal at the harness during a call for heat.
- Spin the shaft by hand: it should turn freely without grit or drag.
- With power and signal present and no rotation, the motor is the fault.
The full sequence, including module versus motor tests, is covered in how to test an ECM blower motor.
Other Flash Codes
2 Flashes: System Lockout
The control gave up after repeated failed ignition attempts or recycles. Read which earlier fault (pressure switch, flame sensing, limit) preceded it. The blower motor is not usually the cause.
3 Flashes: Pressure Switch Fault
Check that the inducer starts, the hose is not kinked or full of water, and the condensate drain and vent are clear. Not a blower motor issue, but the inducer motor is a separate part.
5 Flashes: Flame Sensed with No Flame Expected
Possible gas valve leakage or a board fault. Shut off gas and call a technician.
6 Flashes: Polarity or Ground
Reversed 115 V AC polarity or a poor ground. The IFC is polarity sensitive: the hot leg must land on the black field lead. Have a technician correct the wiring.
7 Flashes: Gas Valve Circuit Error
Check the gas valve harness and connections. A valve or board replacement is a technician job.
8 Flashes: Low Flame Sense Signal
Clean the flame sensor with fine abrasive and verify gas pressure and burner alignment. The blower motor is not involved.
9 Flashes: Igniter Relay Fault
On most boards this is the igniter relay on the control. On the two-stage board in 18-CH76D1, 9 flashes is an open inducer limit, which is not the blower either. Check which legend applies to your board.
Continuous On, Continuous Off and Normal Flashes
Both LEDs continuous on is an internal control failure: replace the IFC. Both continuous off is an open fuse or no power: check the door switch, breaker and low-voltage short before replacing the board. For other codes, the HVAC fault code lookup covers more brands, and the Carrier furnace and AC error codes guide covers that platform.
Which Motor Your Trane Furnace Uses
Trane and American Standard furnaces use constant-torque X13 motors, variable-speed ECM 2.3, 2.5 and 3.0 motors, or EON motors, depending on model and year. The nameplate on the motor (not the furnace model) identifies the part. A remanufactured motor programmed to your OEM part number plugs into the original harness on the great majority of installs. Start with the Trane replacement blower motors page.
How to Reset a Trane Furnace After a Code
- Set the thermostat to off and note the code first.
- Switch power off at the furnace service switch for a short pause, then restore it.
- Set the thermostat to heat and watch one full cycle.
- If the same code returns, the fault is real: do not reset repeatedly.
When to Call a Pro
Call a licensed technician for codes 5, 6 and 7, any gas valve or igniter work, a cracked heat exchanger suspicion, or any repeat lockout. Motor, filter and wheel checks are reasonable for a capable DIY owner with power locked out.
FAQs
What does a continuous red light on a Trane furnace mean?
On the IFC legend, both LEDs continuous on indicates internal control failure, and the control board needs replacing.
What does a Trane furnace blinking red light mean?
Red flashes count a fault code, such as 3 for a pressure switch fault or 4 for an open limit. One red flash every 20 seconds is normal operation.
Is the blower motor the cause of 4 flashes?
Often. An open limit means the furnace overheated, and weak airflow from a failing blower, dirty wheel or clogged filter is the usual cause. Check airflow before replacing the limit switch.
Do American Standard furnaces use the same codes as Trane?
The service guides are published jointly for Trane and American Standard, and the same IFC legend applies. Verify against the blower door label, because two-stage boards differ on codes 6, 9 and 10.
Does resetting the furnace fix an error code?
Resetting clears the code and gives the control a fresh start. If the fault is real, the code returns on the next call for heat.
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