American Standard furnaces built on the same-era platforms use identical codes (Trane Technologies builds both), but the codes below are sourced from Trane’s own installer’s guides for two specific Trane furnace families. Confirm against your unit’s door sticker before you act on any of this: Trane does not use one diagnostic system across its whole lineup.
TL;DR
- Blinking LED? Count two full cycles, then check the table below against your door sticker.
- Digital display showing letters and numbers (like E3.1 or E04)? Your furnace uses a different, newer diagnostic system. Skip to the digital E-code section.
- Code 4 / E04 keeps coming back after a clean filter? Stop resetting it. That code covers the high-limit switch and the rollout switch on the same circuit, and Trane’s own board can’t tell them apart. Repeated trips need a tech, not another reset.
- 1 flash, or a rapid continuous flash? Neither is a documented code on the furnace families Trane publishes flash-code tables for. Recount, or check whether your board uses the digital display instead.
Two different diagnostic systems, not one
Trane furnaces don’t all report faults the same way. Based on Trane’s own installer’s guides:
- Older and mid-efficiency 2-stage condensing furnaces with a variable-speed inducer (the platform closest to what most Trane fault-code searches are looking for) use a single red LED that flashes a counted number of times, with a pause between cycles.
- Newer single-stage induced-draft furnaces use a 7-segment digital display that shows an actual alphanumeric code (e2.1, e04, e6.3, etc.), so no counting is required. The board just tells you.
Open the lower door panel and look at the board before you do anything else. If you see a genuine digit/letter readout, use the digital section below. If you see a single LED blinking, use the flash-code table.
Trane furnace LED flash codes (verified)
Source: Trane’s Installer’s Guide for the 2-stage condensing, variable-speed-inducer furnace family (document 18-CD20D3-21). Count two complete blink cycles to confirm the number, and check it against your unit’s door sticker, since Trane explicitly notes exact assignments can vary by model.
| Flashes | Fault | What it means |
|---|---|---|
| 2 | System lockout | Retries or recycles exceeded: the furnace tried and failed to prove flame enough times that it gave up and locked out. |
| 3 | Draft pressure error | Could be a venting problem, a pressure switch problem, or an inducer problem; the board can’t distinguish which. |
| 4 | Open temperature limit switch | The high-limit switch tripped. This is the same code the rollout switch reports (see the safety note below). |
| 5 | Flame sensed with no call for heat | The board is seeing a flame signal when the gas valve should be closed. |
| 6 | Polarity, grounding, or igniter fault | 115V AC power reversed, a Triac (igniter) fault, poor grounding, or system voltage too low: four different possible causes reported by one code. |
| 7 | Gas valve circuit error | Fault in the gas valve circuit itself. |
| 8 | Low flame sense | Flame current is present but too weak, almost always from a dirty flame sensor. |
| 9 | Open inducer limit switch | The inducer motor’s own limit switch has opened. |
| 10 | Inducer communication error | The control board has lost communication with the inducer motor. |
| Solid on | Internal gas valve error or low thermostat voltage | Not a blink pattern; the LED stays lit. |
| Solid red + solid green | Continuous reset | Caused by a blown fuse or an internal control error. |
There is no 1-flash code and no distinct “rapid continuous flash” code on this platform. If you’re seeing either, recount carefully or check whether your board is actually the digital type instead.
Code-by-code: what to check first
2 flashes: system lockout
The board attempted ignition the maximum number of times (or lost flame and retried the maximum number of times) without success, and locked itself out.
- Turn the thermostat down, then back up, or cycle power at the furnace switch for 30 seconds to clear the lockout.
- Watch the next ignition attempt. If it lights and holds flame, the fault was likely transient (a brief gas supply hiccup, a weak spark).
- If it locks out again, the underlying problem is still there. Check codes 6, 7, or 8 below depending on where ignition is failing, or call a tech if you can’t tell.
3 flashes: draft pressure error
This covers venting, the pressure switch, or the inducer: Trane’s own documentation lists all three as possible causes of one code.
Leading cause on high-efficiency condensing furnaces: a blocked condensate drain. Water backing up from a clogged drain creates back-pressure that keeps the pressure switch from closing correctly.
- Locate the condensate drain (white or clear tubing running from the furnace to a floor drain) and check the trap for standing water.
- Clear it: disconnect the trap, vacuum with a wet-dry vac, flush with water, reinstall.
- If the drain is clear, check the flue/vent pipe for blockage and inspect the pressure switch hose for kinks.
- If all of that is clean, the inducer motor itself may be failing. That’s a tech call.
4 flashes: open temperature limit switch (read the safety note first)
Start with the filter, always. Pull it out and hold it to a light. If you can’t see light through it, replace it: a clogged filter is the single most common cause of a high-limit trip. Wait 10-15 minutes for the heat exchanger to cool, then restore power.
If the filter is clean: confirm every supply register is open, check that nothing is blocking the return grille, and (with power off) confirm the blower wheel spins freely by hand.
Safety note: this code doesn’t distinguish a dirty filter from a cracked heat exchanger. Trane’s own control board wires the rollout switch in series with the main high-limit switch, so both faults report as the identical “open limit” code. If Code 4 returns after a confirmed-clean filter and clear airflow, stop resetting it and call a licensed HVAC tech. A cracked heat exchanger or a genuine rollout event can allow combustion byproducts, including carbon monoxide, into the space, and there’s no way to tell that apart from a dirty filter by flash count alone.
5 flashes: flame sensed with no call for heat
The board is detecting a flame signal when the gas valve should be fully closed. This points to a gas valve that isn’t sealing or a flame sensor generating a false signal.
Turn off the manual gas shutoff valve on the line near the furnace and call a licensed tech. Don’t restart the furnace until it’s been diagnosed. This is a gas-valve safety fault, not a DIY repair.
6 flashes: polarity, grounding, igniter, or low voltage
Trane’s documentation lists four distinct possible causes under this one code: reversed 115V AC line polarity, a failed igniter (Triac) relay, poor equipment grounding, or system voltage that’s too low. That’s a wider net than “bad igniter” alone.
- Check line polarity first. This is the cheapest thing to rule out. If a licensed electrician or you (if comfortable working at the breaker panel) can verify hot/neutral aren’t reversed at the furnace’s power connection, do that before replacing parts.
- Check the igniter visually through the sight glass for a cracked or broken element. See Furnace Hot-Surface Igniter: Symptoms, Testing, and Replacement.
- Check the equipment ground at the furnace’s junction box. A missing or loose ground is a common, cheap-to-fix cause of this code that’s easy to overlook.
- If none of those resolve it, the control board’s Triac driver itself may have failed. That’s a tech call.
7 flashes: gas valve circuit error
A fault in the gas valve’s electrical circuit, not the valve’s mechanical sealing. This is a call-a-pro code: testing the gas valve circuit means working with line voltage and gas components together.
8 flashes: low flame sense (dirty flame sensor)
The flame sensor is detecting flame, but the signal is too weak to hold the gas valve open reliably. The sensor rod has built up an oxide layer that insulates it from the flame’s ionization current.
This is DIY-appropriate and usually a 10-minute fix:
- Turn off furnace power.
- Locate the flame sensor: a metal rod on a ceramic mount inside the burner box, single wire connection.
- Remove the mounting screw and disconnect the wire.
- Clean the rod (not the ceramic insulator) with fine steel wool or an emery cloth.
- Reinstall, restore power, and test.
Full procedure: Furnace Flame Sensor: Symptoms, How to Clean It, and When to Replace.
9 flashes: open inducer limit switch
The inducer motor has its own internal limit switch, separate from the main heat-exchanger high limit, and it has opened. This usually points to an overheating or failing inducer motor rather than an airflow problem. Have a tech test the inducer motor and its limit switch.
10 flashes: inducer communication error
The control board has lost communication with the inducer motor’s control. On variable-speed inducer furnaces this is a wiring or motor-control-board fault, not something to troubleshoot by ear. Tech call.
Digital E-code models
Trane’s newer single-stage induced-draft furnaces (the A801X control platform) skip counted flashes entirely and show an alphanumeric code directly on a 7-segment display. Partial list, sourced from Trane’s own installer’s guide for this platform:
| Code | Meaning |
|---|---|
| e2.1 | Retry exceeded: flame never sensed, locked out after 3 attempts |
| e2.2 | Recycles exceeded: flame sensed then lost, locked out after 10 times |
| e3.1 | Shorted pressure switch (1st stage) |
| e3.2 | Open pressure switch (2nd stage) |
| e04 | Open limit: main thermal switch, rollout switch, or reverse-airflow switch (same shared-circuit caveat as Code 4 above) |
| e05 | Flame detected when it shouldn’t be present |
| e6.1 | Reversed voltage polarity |
| e6.2 | Bad grounding |
| e6.3 | Igniter relay failure or open igniter |
| e08 | Flame current low but still holding |
| e11 | Gas valve energized/de-energized incorrectly (five possible sub-causes on the valve relay) |
| e12 | Open fuse |
If your display shows something not on this list, it’s a different furnace family than either platform this guide verifies against. Go by your door sticker or model-specific service manual rather than guessing from a table that doesn’t match your board.
When to call a licensed HVAC technician
- Code 5 / e05 (flame without call), Code 7 (gas valve circuit): gas-valve faults, call immediately.
- Code 4 / e04 that returns after a confirmed-clean filter: possible rollout or cracked heat exchanger. Don’t keep resetting it.
- Code 9 or 10: inducer motor or communication faults, not diagnosable without test equipment.
- Any code that comes back after your first DIY fix attempt.
- Anything involving the gas line, the sealed combustion chamber, or line-voltage wiring.
FAQ
Are American Standard furnace codes the same as Trane? On equivalent-era platforms, yes: American Standard and Trane are both Trane Technologies brands and share control board designs. But confirm against your own unit’s door sticker, since (as this guide shows) even within Trane’s own lineup, code assignments differ between furnace families.
How do I reset a Trane furnace after a lockout? Turn the power switch off (the wall switch near the furnace, or the toggle on the unit itself) for about 30 seconds, then restore it. This clears the lockout and lets the board retry. If the fault was a one-time event, it may run fine afterward; if the underlying cause is still there, it will lock out again.
My Trane furnace Code 4 clears when I reset it, but comes back every few hours. What’s wrong? Don’t keep resetting it. Code 4 covers the main limit switch and the rollout switch on the same circuit, and Trane’s board has no way to tell you which one tripped. Recurring trips after a confirmed-clean filter and clear airflow warrant a technician inspection, not another reset. The underlying cause could be a marginal blower motor, a stuck-open limit switch, or a cracked heat exchanger.
The sticker on my furnace door is missing. Where do I find my model’s actual codes? Find your model number (on the rating plate inside the door or on the cabinet side) and search it with “installer’s guide” or “service facts.” Trane publishes its installer’s guides through its eLibrary at elibrary.tranetechnologies.com. That’s the source this guide itself is verified against, and it’s the same source your specific model’s exact code table lives in.
Related guides
- Trane HVAC: Brand Overview, Reliability, and Repair Help: product lines, reliability, and Trane vs. American Standard explained.
- Furnace Not Heating: Causes, Diagnostic Order, and What to Do First: if no fault code is showing at all.
- Furnace Flame Sensor: Symptoms, How to Clean It, and When to Replace: full procedure for Code 8 / e08.
- Furnace Hot-Surface Igniter: Symptoms, Testing, and Replacement: full procedure for Code 6 / e6.3.
- Carrier vs. Trane: Which Brand is Better?: if a fault code is pointing toward replacement rather than repair.
