Which models this covers
Trane and American Standard *UH1 / *DH1 condensing gas furnaces with LED codes (Installer’s Guide 18-CD29D1-14), and S9X2 furnaces with a 7-segment display (wiring diagram in 22-1930-1G). S8X, XV/XR and IntelliComfort boards weren’t reviewed and may differ. Codes differ between control boards, so check the code chart printed on your unit or in its manual if your model isn’t listed.
How to read the code
Look through the window on the furnace door. Count the flashes between pauses on LED models, or read the code on the display of S9X2 models. Trane’s guides list these as technician diagnostics. The homeowner checks below are common, safe starting points.
LED flash codes (*UH1 / *DH1)
| Code | What it means | What to do |
|---|---|---|
| Slow flash | Normal, no call for heat | None. |
| Fast flash | Normal, call for heat | None. |
| Steady on | Control board failure | Call a pro.Pro |
| Off | No power | Check the furnace power switch and breaker. |
| 2 | System lockout (ignition retries or recycles exceeded) | Check the gas is on, then reset power. If it repeats, call a pro.Pro |
| 3 | Draft pressure error (venting, pressure switch or inducer) | Check outdoor vent pipes for snow, ice or blockage. If clear, call a pro.Pro |
| 4 | Open high limit | Replace a dirty filter and open closed vents. If it repeats, call a pro.Pro |
| 5 | Flame sensed when there should be none | Turn off the furnace and call a pro.Pro |
| 6 | 115V power reversed, or poor grounding | Call a pro or electrician.Pro |
| 7 | Gas valve circuit error | Call a pro.Pro |
| 8 | Low flame-sense signal | Call a pro. The flame sensor often needs cleaning.Pro |
| 9 | Igniter circuit / grounding problem | Call a pro.Pro |
S9X2 display codes
| Code | What it means | What to do |
|---|---|---|
| E01 | Internal control failure | Call a pro.Pro |
| E2.1 | Ignition retries exceeded | Check the gas is on, then reset power. If it repeats, call a pro.Pro |
| E2.2 | Recycles exceeded, or pressure switch opened 10 times | Check vent pipes for blockage. Otherwise, call a pro.Pro |
| E2.3 | First-stage gas valve not energized (10+ times) | Call a pro.Pro |
| E3.1 / E3.2 | First-stage pressure switch shorted / open | Check vent pipes for blockage. Otherwise, call a pro.Pro |
| E3.3 / E3.4 | Second-stage pressure switch shorted / open | Call a pro.Pro |
| E04 | Open limit, rollout or reverse-airflow switch | Replace a dirty filter and open vents. If it repeats or a rollout tripped, call a pro.Pro |
| E05 | Flame sensed when there should be none | Turn off the furnace and call a pro.Pro |
| E6.1 / E6.2 | Reversed polarity / bad ground | Call a pro or electrician.Pro |
| E6.3 | Igniter relay failed or igniter open | Call a pro.Pro |
| E7.1 | Gas valve energized when it should be off | Turn off the furnace and call a pro.Pro |
| E08 | Low flame current | Call a pro.Pro |
| E09 | Inducer limit or condensate switch open | Check that the condensate drain isn’t clogged. Otherwise, call a pro.Pro |
| E11 | Gas valve / relay fault | Call a pro.Pro |
| E12 | Open fuse | Call a pro.Pro |
Sources
These codes are transcribed from the manufacturer’s own documentation. Many websites repeat codes that don’t match the manuals, so when in doubt, trust the chart on your unit.
- Trane/American Standard Installer’s Guide 18-CD29D1-14 (*UH1/*DH1)
- Trane S9X2 Installer’s Guide 22-1930-1G (wiring diagram codes)
Code pointing to a big repair? Check whether to repair or replace before you pay for it.
Frequently asked questions
What does 3 flashes mean on a Trane furnace?
On Trane and American Standard *UH1/*DH1 furnaces, 3 flashes is a draft pressure error: the pressure switch didn’t confirm proper venting. Check the outdoor intake and exhaust pipes for snow, ice or blockage. If they’re clear, call a pro to check the inducer and pressure switch.
What does 6 flashes mean on a Trane furnace?
Trane’s installer guide lists 6 flashes as reversed 115V polarity or poor grounding, not low voltage as some sites say. It’s a wiring issue for a technician or electrician.
Are Trane and American Standard furnace codes the same?
Trane and American Standard are made by the same company and share these furnace platforms. The model’s first letter (T or A) is the brand. Codes can still differ by control board, so check the label inside your furnace door.