Trane Furnace Error Codes List: Every Code Explained
Every Trane furnace error code we could verify against Trane's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.
How to read and retrieve error codes on Trane furnaces
Trane boards provide the fault history through the LED pattern and, on communicating models, through the thermostat's installer menu, which lists stored alert codes (the alphanumeric family). The fault chart on the blower door is the authority for your unit — Trane changed flash-pattern assignments between generations, and charts copied between websites frequently mix them up.
The complete Trane furnace error code list
| Code | Meaning | Most likely cause | First fix |
|---|---|---|---|
| 2 Flashes | System lockout; ignition retries or recycles exceeded | Repeated failed ignition or flame loss, from gas supply, ignitor, flame sensor or pressure switch problems | Confirm the thermostat calls for heat and gas supply to the home is on; do not keep resetting, call a licensed HVAC technician |
| 3 Flashes | Pressure switch fault — the pressure switch did not close (or the inducer/vent proof failed) on Trane furnaces with LED blink diagnostics. | Blocked vent/intake | Clear vents; clean the condensate path; replace bad tubing. |
| 4 Flashes | Open temperature limit circuit; the furnace overheated and shut the burners down | Clogged filter, blocked registers or returns, failing blower, or an open limit switch | Replace the filter and open all registers and returns; repeat trips need a licensed HVAC technician |
| 5 Flashes | Flame sensed when no flame should be present | Leaking or stuck gas valve, lingering burner flame, or a flame sensing circuit fault on the control | Turn the furnace off; gas valve and flame sensing faults need a licensed HVAC technician |
| 6 Flashes | 115 volt AC power reversed, ignitor (triac) fault, poor grounding, or system voltage too low | Reversed line polarity, missing or poor equipment ground, low supply voltage, or a failed ignitor output on the control | Do not operate on suspect wiring; polarity, grounding and control checks are licensed HVAC technician or electrician work |
| 7 Flashes | Gas valve circuit error | Shorted or open gas valve wiring, failed gas valve coil, or a control board gas valve output fault | Gas valve circuit diagnosis is licensed HVAC technician work; do not keep resetting the furnace |
| 8 Flashes | Low flame sense signal | Coated flame sensor, poor unit ground, or a weak burner flame from gas pressure problems | Flame sensor cleaning and gas pressure checks are licensed HVAC technician work |
| 9 Flashes | Open inducer limit switch on *UX2/KIT-chart boards; older UC/XB-chart boards use 9 flashes for the ignitor circuit check | Tripped inducer limit from inducer overheating, or on older boards an open ignitor circuit or excess neutral-to-common voltage | Turn the furnace off and let it cool; inducer limit and ignitor circuit work is licensed HVAC technician work |
| 10 Flashes | Inducer communication error | Failed communication between the integrated control and the variable-speed inducer motor, or a damaged inducer harness | Power-cycle once at the furnace switch; inducer and control diagnosis is licensed HVAC technician work |
| CONTINUOUS ON | Solid red LED: internal gas valve (GV) error or low thermostat (TH) voltage on *UX2/KIT-chart boards; older UC charts mark solid red as replace the IFC | Internal control or gas valve circuit failure, or low 24-volt thermostat-circuit voltage | Try one power reset at the furnace switch; a persistent solid red LED needs a licensed HVAC technician |
| E0 | Internal failure on A801X-family controls; the same internal-failure family shown as E01 on S-series controls | Failed integrated furnace control electronics | Try one power reset at the furnace switch; control replacement is licensed HVAC technician work |
| E01 | Loss of the IRQ or other internal control failures | Internal integrated control fault or corrupted control operation | Try one power reset at the furnace switch; a persistent E01 is control board work for a licensed HVAC technician |
| E2.1 | Retry exceeded; flame was never established during the ignition retries | No gas flow, a failed ignitor, or a flame sensor that never proved flame | Confirm gas supply to the home is on and the thermostat calls for heat; ignition diagnosis is licensed HVAC technician work |
| E2.2 | Recycles exceeded; flame was established then lost repeatedly, or the first-stage pressure switch opened ten times | Interrupted gas supply, coated flame sensor, weak flame, or a pressure switch dropping out during operation | Clear vent and intake terminations and check the condensate drain; persistent recycles need a licensed HVAC technician |
| E2.3 | First-stage gas valve not energized when it should be, ten times within one call for heat | Control not sending 24 volts to the low-stage gas valve, a loose gas valve plug, or an internal control relay fault | Gas valve voltage and control diagnosis is licensed HVAC technician work |
| E3.1 | Shorted (stuck closed) pressure switch, first stage | Pressure switch contacts stuck closed, or wind pressure holding the switch closed at the vent termination | Check the vent termination is clear; switch testing is licensed HVAC technician work |
| E3.2 | Open pressure switch, first stage; draft was not proven | Blocked vent or intake, clogged condensate drain, damaged switch hose, or a weak inducer | Clear vent and intake terminations and check the condensate drain; then a licensed HVAC technician |
| E3.3 | Shorted (stuck closed) pressure switch, second stage (two-stage models) | Second-stage pressure switch contacts stuck closed, or shorted switch wiring | Check the vent termination is clear; switch testing is licensed HVAC technician work |
| E3.4 | Open pressure switch, second stage; high-stage draft was not proven (two-stage models) | Vent or intake restriction at high inducer speed, condensate backup, hose fault, or a weak inducer | Clear vent and intake terminations and check the condensate drain; then a licensed HVAC technician |
| E04 | Open thermal limit, rollout switch, or reverse airflow switch | Overheating from a clogged filter or blocked airflow, flame rollout, or a failed switch in the series limit circuit | Replace the filter and open all registers and returns; do not reset a rollout repeatedly, call a licensed HVAC technician |
| E05 | Flame detected when it should not be present | Leaking gas valve keeping a flame alive, a shorted flame sense wire, or a grounded flame sensor | Turn the furnace off; gas valve and flame sense faults need a licensed HVAC technician immediately |
| E6.1 | Voltage reversed polarity at the furnace supply | Hot and neutral line wires reversed at the furnace or junction box | Do not operate on reversed polarity; correction is licensed HVAC technician or electrician work |
| E6.2 | Bad grounding at the furnace | Missing or poor equipment ground, or a loose burner or control ground connection | Grounding correction is licensed HVAC technician or electrician work |
| E6.3 | Igniter circuit fault: the igniter relay fails or the igniter is open | Cracked or burned-out igniter, open igniter wiring, or a failed control igniter relay | Igniter and control diagnosis is licensed HVAC technician work; do not handle the igniter element |
| E7.1 | First-stage gas valve (MVL) is energized when it should be off | Stuck gas valve relay on the control, or shorted gas valve wiring holding the valve on | Shut off gas and power to the furnace; call a licensed HVAC technician immediately |
| E08 | Flame current is low, but still strong enough to allow operation | Coated flame sensor, poor sensor position in the flame, or a weak flame from gas pressure problems | Flame sensor cleaning and flame current measurement are licensed HVAC technician work |
| E09 | Platform-specific Trane code (communicating/ComfortLink-era systems render faults in E-format) — not part of Trane's classic blink-code list; the model/thermostat documentation defines the branch. | A system fault rendered in communicating format | Follow the named subsystem's standard diagnosis (ignition/flame-sense, pressure, limit families) once the alert text identifies it. |
| E11 | Gas valve fault group: a gas valve not energized when it should be, or a gas valve relay stuck closed | Failed control gas valve relay, open or shorted valve wiring, or a failed gas valve | Gas valve and control work is licensed HVAC technician work; do not keep resetting |
| E12 | Open fuse on the integrated furnace control | A short in the 24-volt thermostat or component wiring blowing the board fuse | Check thermostat wiring for visible damage; fuse replacement and short tracing are licensed HVAC technician work |
| Ht1 | Status display, not a fault: first-stage heating is running | Normal operation on a first-stage call for heat from the thermostat | No fix is needed if the home is heating; a fault would appear as an E code on the same display |
| Ht2 | Status display, not a fault: second-stage heating is running | Normal operation on a second-stage call for heat; a single-stage thermostat jumpered W1-W2 shows Ht2 at all times | No fix is needed if the home is heating; a fault would appear as an E code on the same display |
| IdL | Status display, not a fault: the furnace is idle | No call for heat, cooling or fan from the thermostat | Set the thermostat to heat and raise the setpoint if heat is wanted; otherwise no action is needed |
| SOLID RED WITH SOLID GREEN | Continuous reset, caused by a blown fuse or internal error | Blown low-voltage fuse on the control, a short in 24-volt wiring, or an internal control failure | Note any recent thermostat work for the technician; fuse and short tracing is licensed HVAC technician work |
How to reset / clear error codes on Trane furnaces
Trane furnaces report faults as red-LED flash patterns on the control board (count the flashes between pauses) on non-communicating models, and as alphanumeric codes on communicating/XV models. Soft lockouts retry automatically; hard lockouts clear by fixing the cause and cycling power at the furnace switch. The board stores recent faults — on many models the LED keeps the last fault flash pattern available until the next successful cycle overwrites it.
How to diagnose any Trane furnace code
Work the problem in this order — and stop at any point where gas, combustion or mains wiring is involved, because those belong to a licensed HVAC technician: (1) record the code exactly: count LED flashes slowly, twice, or photograph the alphanumeric display; (2) check the free things homeowners legitimately own: the thermostat is calling for heat, the furnace power switch and breaker are on, the filter is not clogged solid (a starved furnace overheats and locks out on limit codes), all vents and the return are open, and the condensate drain is not blocked on condensing models; (3) reset once — at the power switch, off for 30 seconds — then watch a full call for heat from the beginning: inducer, ignition, flame, blower, in that order; where the sequence stops is the fault family the code names; (4) a code that returns immediately is an active fault — do not keep resetting a lockout, especially any flame or limit code; (5) everything inside the burner compartment — flame sensor cleaning is the one grey area many manuals allow owners, but gas valves, burners, heat exchangers and control boards are professional work. If you smell gas at any point, leave and call the gas utility, not a helpline.
Flash counts on older boards, E-codes on communicating furnaces
Trane furnaces report faults two ways depending on generation. The integrated furnace control on most models flashes a red LED in counted patterns, read against the fault chart printed in the installation manual and on the unit — that chart, for your exact model, is the authority. Trane's communicating and modulating furnaces (the S-series and XV generation) instead show alphanumeric E-codes on a display and store a fault history. The table below covers both dialects and keys each entry the way Trane displays it, because a "4 flashes" fault and an E-code with a similar number are unrelated reports.
Lockouts are the furnace protecting itself, not a second fault
After repeated failed attempts at the same step — ignition above all — a Trane control stops trying and locks out for a period rather than cycling forever against a fault that could overheat the furnace or flood the burners with unburned gas. A lockout is evidence, not damage: it tells you the same step failed repeatedly. Reset once, at the power switch, and watch one full call for heat from the start — inducer, pressure proof, ignition, flame, blower — because where the sequence stops is the fault family. A code that returns immediately is an active fault; do not keep resetting it, and leave everything inside the burner compartment to a licensed HVAC technician.
Blink codes, display codes and lockouts
Two generations of fault reporting live side by side on modern furnaces. Older and simpler boards report through a single LED: a repeating count of flashes, read slowly against the chart printed inside the blower door — that chart, for your exact model, outranks any list on the internet, including this one. Newer communicating furnaces show alphanumeric codes (the E-series in the table above) and store a fault history a technician can scroll. Both generations share the lockout idea: after a set number of failed attempts at the same step — ignition is the classic — the board stops trying for a period (often an hour, or until power is cycled) instead of cycling forever against a fault that could overheat or flood the burners with unburned gas. A furnace in lockout is not broken by the lockout itself; it is a furnace that has already failed the same step repeatedly and is waiting for someone to find out why.
Furnace codes are also seasonal in a way washer codes are not. The first cold snap produces a wave of ignition and flame codes from furnaces that sat idle all summer — oxidised flame sensors, spider-nested burners, pressure-switch hoses holding condensate from the cooling season. Deep-winter adds frozen condensate lines on high-efficiency models and intake/exhaust terminations blocked by snow or ice, which present as pressure-switch codes. A code that appears once, on the coldest night of the year, and never again has often met its cause already; a code that appears every cycle, in any weather, is a component asking to be tested.
The most searched Trane furnace codes, in detail
E09 — Platform-specific Trane code (communicating/ComfortLink-era systems render faults in E-format)
Trane furnaces historically speak in control-board blink codes; the communicating systems (ComfortLink/XL-series thermostats) render faults as E-codes on the thermostat, with the definitions in that system's documentation. E09 doesn't carry a single cross-platform Trane definition. The reliable approach mirrors Goodman's clarifications: note exactly which stage the furnace reaches (inducer, ignition, flame, blower), check the communicating thermostat's alert screen for its fuller description (these systems usually spell the fault in words alongside the code), and let the model documentation assign the branch.
Most likely cause: A system fault rendered in communicating format — The thermostat's alert detail names the subsystem — read it before searching the code.
First check: Open the thermostat's alert/notification screen — ComfortLink systems describe faults in words.
If it keeps coming back: The thermostat keeps an alert history — a goldmine for the technician; don't clear it before a visit.
3 Flashes — Pressure switch fault
On Trane's blink-code furnaces, 3 flashes is the pressure-switch family: the inducer ran but the switch didn't prove draft (on many Trane charts, 3 flashes covers pressure switch stuck open/closed variants — the chart inside the blower door is the authority for your exact model). The diagnosis is the universal pressure-switch chain: vent/intake blockage (snow and nests lead), condensate trap/drain on condensing models, the switch's tubing (cracked or water-filled), inducer strength, and the switch itself last.
Most likely cause: Blocked vent/intake — Snow, ice, nests — the winter classic.
First check: SAFETY: never jumper a pressure switch to 'test' heating — it proves exhaust can leave.
If it keeps coming back: Cold-snap recurrence = termination icing or a freezing condensate line; rainy-day recurrence = vent water/sag.
Less common and model-specific codes
Search data shows owners also meet these codes on Trane furnaces: 7P1, E2, E24, E3, E4, E6, Fixes, HE1, HE2. They are not part of the core code list Trane publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.
Related guides
Facts on this page were checked against manufacturer documentation: manuals.plus · manuals.plus · manuals.plus · manuals.plus · www.nee.ca · springhome.ca