What do Trane and American Standard furnace error codes mean?
Trane and American Standard furnaces flash 2 for lockout, 3 for a pressure switch and 4 for an open limit, per Trane's guide 18-CH111D1-1A. Code 5 means flame sensed with no flame. Your door chart still decides.
Key points
- Trane's Service Installer's Guide 18-CH111D1-1A lists TDX and TUX (Trane) and ADX and AUX (American Standard) furnaces on one control and one chart.
- The chart runs from 1 to 9 flashes. 1 is normal, 2 is lockout, 3 pressure switch, 4 open limit, 5 flame sensed when it should not be, 6 reversed power or poor ground, 7 gas valve circuit, 8 low flame signal, 9 igniter relay.
- Other Trane and American Standard models may use other boards, so your door chart or manual is the authority.
- Read the light through the sight glass with the door on. Leave the power on until you have counted.
- Safe checks are thermostat, breaker and furnace switch, filter, PVC pipes and condensate. Limit and flame-sensed codes are stop-and-call.
On a Trane or American Standard furnace, the fault code is the number of times a small LED on the control board flashes, visible through the sight glass in the lower door: 2 is lockout, 3 a pressure switch fault, 4 an open limit and 5 flame sensed with no flame. Count it with the door on, write it down, and match it to the chart below or, better, the one on your furnace door.
Do Trane and American Standard really share boards and charts?
For the models listed here, yes. Trane's Service Installer's Guide 18-CH111D1-1A (dated 22 Dec 2023) covers a replacement integrated furnace control for two-stage furnaces. It lists model families that begin with TDX and TUX, which are Trane furnaces, and ADX and AUX, which are American Standard furnaces. All of them take the same control, and the guide prints one diagnostic code chart for all of them.
The limits matter. That document applies to the model families it lists. A different series could carry a different control with different codes, so if your model number is not in the guide's list, rely on your own manual.
How do you find the chart on your furnace?
- Look at the back of the lower blower door for the diagnostic label.
- Check beside the control board for a second label.
- Read the model number off the rating plate inside the cabinet. Trane and American Standard publish installation and service documents for each model, and the troubleshooting section holds the chart.
Write down the model number and the pattern before you call anyone.
How do you read the code safely?
Use the sight glass. Many doors have a small window so you can see the LED with the door on.
- Leave the door on. On most gas furnaces a door switch cuts power when the blower door comes off, and the code may not show again.
- Watch for a full cycle. In the guide's chart, fault codes are counted flashes. A slow flash is normal with no call for heat, and a fast flash is normal with a call for heat.
- Count and write it down before power is cycled. A repeated pattern with a pause is the code.
- Photograph the chart and the rating plate.
What do the codes on the Trane and American Standard chart mean?
This is the chart from guide 18-CH111D1-1A, for the control used in the TDX, TUX, ADX and AUX models it lists.
| Flashes | Meaning on Trane's chart |
|---|---|
| 1 | Normal operation. Flash every 20 seconds |
| 2 | System lockout: retries or recycles exceeded |
| 3 | Pressure switch fault |
| 4 | Open limit switch |
| 5 | Flame sensed when no flame should be present |
| 6 | 115-volt AC power reversed or improper ground |
| 7 | Gas valve circuit error |
| 8 | Low flame sense signal |
| 9 | Igniter relay fault |
| Slow flash | Normal, no call for heat |
| Fast flash | Normal, call for heat present |
| Continuously on | Internal control failure |
| Continuously off | Fuse open |
The guide's chart has a column for a green LED and a column for a red LED. Which one your board uses depends on the board, which is another reason to read the label on your own door.
What do the common families usually mean?
Pressure switch (3 flashes). The control could not prove the inducer is venting exhaust. In Minnesota the usual causes are frost or snow over the PVC pipes, a frozen or plugged condensate line, or a cracked hose. Our pressure switch guide walks through it, and so does frozen condensate lines.
Limit (4 flashes). The furnace overheated and shut off. That points to airflow: filter, closed registers, blocked return. See what a limit switch does.
Ignition lockout (2 flashes). The furnace tried and gave up. The cause is something else on the list, such as the flame sensor, igniter or gas valve circuit.
Flame sense (5 or 8 flashes). 8 is a low signal, often a dirty or worn sensor. 5 means flame was sensed when none should be there, which is a stop-and-call code.
Rollout. The chart in this guide does not give rollout its own flash count, so none is assigned here. Rollout switches are manual-reset safeties on many furnaces. Flame coming out of the burner area is a technician problem, not a reset.
What can you safely check yourself?
Run the basic checks in our general furnace light codes guide: thermostat, breaker and furnace switch, filter, snow on the PVC pipes and water at the furnace. Restart the furnace once, then watch the next cycle. A returning count means stop.
When should you call?
Call if the code returns after one restart, if it is a limit, flame-sensed or gas valve code, if the light is off with power on, or if your furnace does not match the chart. Tell us the brand, model number and flash count. We work on both Trane and American Standard furnaces. Hours are 7am to 9pm, seven days a week. See furnace repair in Minneapolis. The trip charge is $79, waived when you approve the repair, with a written flat-rate price before work starts. Call 612-429-3465. Other brands use different charts; the general guide is what the blinking light means.
Common questions about heating
What does a slow versus fast flash mean on a Trane furnace?
On the control in Trane's guide, a slow flash means normal operation with no call for heat, and a fast flash means normal operation with a call for heat present. A light that stays on continuously means internal control failure, and a light that stays off means the fuse is open. Fault codes are counted flashes from 2 to 9.
Should I turn off the power to read the code again?
Not before you have counted it. Many controls show the fault only while powered, and pulling the blower door usually opens the door switch and cuts power. Watch through the sight glass, write the pattern down, then make the safe checks. One restart afterward is reasonable. If the same count returns, the cause is still there and it is time to call.
Is 3 flashes on a Trane furnace the same as 3 flashes on every brand?
No. Flash counts are not universal. On the Trane and American Standard chart in guide 18-CH111D1-1A, 3 flashes is a pressure switch fault, but other brands use different numbers and some use two-digit codes. Always read the chart for your own furnace, never a list from another brand.
Why does my Trane furnace flash the same code after a reset?
A reset clears the display, not the cause. If the same count returns, the fault is still there: a blocked vent for 3 flashes, restricted airflow for 4, a dirty sensor for 8. Check the filter, thermostat setting and outdoor PVC pipes once, then stop. Repeated resets only stress the parts, so call for service.