Trane furnaces show faults as LED flashes on older boards, or as E codes such as E2.1 on the S-series control display. Communicating systems send a numbered alert to the ComfortLink II thermostat. Note the code and model, check the filter and thermostat setting, and reset once: on older flash-code furnaces Trane's reset is power off, on, off and on within 30 seconds. If the code returns, call a dealer.
Trane error codes show up in three places: on the furnace control board (a flashing LED on older furnaces, or a small display that flashes E codes such as E2.1 on S-series furnaces), on a ComfortLink II thermostat as a numbered alert, and on communicating XV outdoor units as alert codes. Write down the code and the model number first. Then check the filter and the thermostat setting, and if the code comes back after one reset, call a Trane dealer.
Every table below comes from Trane's own installer's guides and service facts, which are published for both Trane and its sister brand American Standard. We name the document and the model series under each table, because the codes are not the same on every Trane furnace.
If you smell gas, stop here
A gas smell is not a code to look up. Leave the house and call your gas supplier from outside. Trane's guide to a furnace that won't turn on says a rotten-egg smell may mean a gas leak, and to leave the house and call your gas company.
Where a Trane furnace shows its code
Trane's page on a blinking furnace light says a slow green blink may just mean there is no call for heat, and a faster, continuous green blink means the furnace is heating. Red blinking generally signals a problem. Some older furnaces have the light on the outside of the cabinet. On others it sits on the control board behind the front panel.
Trane's advice is not to take the front panel off while the furnace is running. Some units have a blower door switch that cuts power and gas when the door comes off. Note the light pattern or code you can see, plus the brand and model, and tell the dealer when you book.
Trane S-series furnace display codes
Trane's S9 and S8 furnaces have a small seven-segment display on the control board instead of a single flashing light. Trane's S9X1, S9X2 and S9B1 installer's guide (18-CE12D1-1D-EN, page 108) explains that when an error occurs, an E code flashes in turn with the system mode and the airflow setting. The table is its "Integrated Furnace Control Display Codes" list, in plain English.
| Code | What it means | What you can check | Call a pro? |
|---|---|---|---|
| E01 | Internal control board error | Nothing | Yes |
| E2.1 | Retries exceeded: flame never sensed. One-hour lockout after 3 tries | Thermostat set to Heat and above room temperature | Yes, if it returns |
| E2.2 | Recycles exceeded: flame sensed, then lost. One-hour lockout after 10 times | Filter | Yes, if it returns |
| E2.3 | First-stage gas valve not energized when it should be, 10 times | Nothing | Yes |
| E3.1 | First-stage pressure switch shorted | Nothing | Yes |
| E3.2 | First-stage pressure switch open | Nothing | Yes |
| E3.3 | Second-stage pressure switch shorted (two-stage models only) | Nothing | Yes |
| E3.4 | Second-stage pressure switch open (two-stage models only) | Nothing | Yes |
| E04 | Open limit: main thermal limit, rollout switch or reverse airflow switch | Replace a dirty filter; keep return vents clear | Yes, if it returns |
| E05 | Flame detected when there should be none | Nothing | Yes |
| E6.1 | Line voltage polarity reversed | Nothing | Yes |
| E6.2 | Bad grounding | Nothing | Yes |
| E6.3 | Igniter relay failed, or igniter open | Nothing | Yes |
| E7.1 | First-stage gas valve energized when it should be off | Nothing | Yes |
| E08 | Flame current low, but still strong enough to run | Nothing | Yes, soon |
| E09 | Open inducer limit switch or condensate pressure switch (S9 condensing models) | Nothing | Yes |
| E11 | Gas valve or gas valve relay fault (first or second stage) | Nothing | Yes |
| E12 | Open fuse on the control board | Nothing | Yes |
The 80% furnaces use the same list minus E09. Trane's S8X1, S8X2 and S8B1 installer's guide (18-CE16D1-1C-EN, page 58) prints every other code with the same meaning. On single-stage S9X1, S9B1, S8X1 and S8B1 furnaces, the second-stage codes do not apply.
The board also stores the last 6 faults in an "L6F" menu, reached with the Menu and Option buttons on the board. That means working inside the cabinet with power on, so leave it to the technician.
Older Trane furnace LED flash codes
Older Trane and American Standard furnaces flash a single light instead. These codes are from Table 21 of the *UH1 and *DH1 condensing furnace installer's guide (18-CD29D1-14-EN, 2016). The star stands for the first letter, which the guide says may be A (American Standard) or T (Trane).
| Light | What it means | What you can check | Call a pro? |
|---|---|---|---|
| Flashing slow | Normal, no call for heat | Nothing; normal | No |
| Flashing fast | Normal, call for heat | Nothing; normal | No |
| On, steady | Replace the control board | Nothing | Yes |
| Off | Check power | Furnace switch and breaker on | Yes, if power is on |
| 2 flashes | System lockout: retries or recycles exceeded | Reset once (see below) | Yes, if it returns |
| 3 flashes | Draft pressure error: venting, pressure switch or inducer problem | Nothing | Yes |
| 4 flashes | Open high limit | Replace a dirty filter | Yes, if it returns |
| 5 flashes | Flame sensed when there should be none | Nothing | Yes |
| 6 flashes | 115-volt power reversed or poor grounding | Nothing | Yes |
| 7 flashes | Gas valve circuit error | Nothing | Yes |
| 8 flashes | Low flame sense signal | Nothing | Yes, soon |
| 9 flashes | Igniter circuit, or a possible grounding problem | Nothing | Yes |
Older boards are not all the same. Trane's replacement control kit guide for *UD and *DD furnaces (2013) prints its own table with separate green, amber and red lights. If your furnace has a code label on the door, that label is the one to trust.
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What to do for the common furnace codes
Lockout: E2.1, E2.2 or 2 flashes
The furnace tried to light and failed, or lit and lost the flame, too many times in a row. On S-series furnaces it waits an hour and tries again. Trane's page on a furnace hard lockout says the first one or two stops are soft lockouts, and a third becomes a hard lockout that a technician has to reset after fixing the cause.
For the *UH1 and *DH1 furnaces, the guide gives the reset: turn the power off, on, off and on again within 30 seconds, at the furnace power source or at the thermostat. Do it once. Before that, confirm the thermostat is on Heat and set above room temperature, which is the first check on Trane's furnace-not-turning-on page.
Open limit: E04 or 4 flashes
The furnace got too hot and a safety switch opened. Low airflow is the usual reason, and the filter is the one thing Trane's lockout page says you should fix yourself. Trane suggests changing standard filters every 30 to 90 days and keeping return vents clear.
Some Trane furnaces also have a manual-reset limit on the burner box. The *UH1 guide says to check the vent and combustion air pipe ends outside for blockage first. If nothing is blocked, a qualified servicer has to reset that switch.
Pressure switch: E3.1 to E3.4, E09 or 3 flashes
The pressure switch proves the draft inducer is pulling combustion gases out through the vent. The *UH1 guide lists wind over 40 mph against the vent, a blocked vent and a blocked or frozen condensate drain as causes, and says the furnace won't run until the drain flows freely. Tell the technician if it happens on windy or freezing days. The switch, inducer and drain trap are their work.
Flame, power and gas valve codes
E05, E6.1, E6.2, E7.1, E11, and 5, 6, 7 or 9 flashes point at the flame sensor, the wiring, the grounding or the gas valve. None of these has an owner step in Trane's literature. E08 and 8 flashes mean a weak flame signal while the furnace still runs, so book a visit soon.
Trane thermostat alert codes (ComfortLink II XL1050)
A communicating Trane system reports faults on the thermostat instead. The XL1050 user guide shows notifications and system alerts on the home screen, and the Menu screen has a System Information section with Alerts. The XL1050 installation guide (section 9.3.1) adds a Diagnostics screen with current alerts and the last 30 days of cleared alerts. Selecting an alert gives a description and possible causes.
| Severity | What Trane says it means | Where it shows | Call a pro? |
|---|---|---|---|
| Critical | Heating or cooling lost; service call required | Home screen | Yes |
| Major | Reduced function; service not needed right away | Not on the home screen | Yes, soon |
| Minor | Should recover, or information only | Diagnostics screen only | No |
The alert itself reads as Err with a number and a sub-code. The installation guide's one example is Err.126.00, which means the outdoor unit is not reporting, so the heat pump stays off while the furnace or electric heat runs. The number comes from the equipment that raised the alert, so look it up in the furnace or outdoor unit table below. Trane does not print a full alert list in either XL1050 guide.
Communicating furnace alert codes
Trane's modulating communicating furnaces flash a red alert LED on the board and send an alert number to the thermostat. These are from Table 24 of the *UHM and *DHM installer's guide (18-CD30D1-20-EN, page 55).
| Alert code | Red LED | What it means | Call a pro? |
|---|---|---|---|
| 1 | 3 flashes | Pressure switch open or shorted (first, second or third stage) | Yes |
| 4 | 8 flashes | Low flame signal; still runs | Yes, soon |
| 10 | 6 flashes | Igniter or triac fault | Yes |
| 18 | Solid on | Internal control failure | Yes |
| 19 | None | Twinning not allowed with variable speed | Yes |
| 20 | 2 flashes | Flame lost or ignition failed; furnace retries | Yes, if it repeats |
| 22 | 2 flashes | Soft lockout: 10 recycles or 3 failed ignitions in one call for heat, one-hour lockout | Yes, if it repeats |
| 26 | 4 or 9 flashes | High temperature limit: heat exchanger or flue gas too hot, possibly low airflow or fan failure | Yes, if it repeats |
| 33 | 6 flashes | Line voltage polarity reversed | Yes |
| 34 | 5 flashes | Flame detected when there should be none | Yes |
| 59 | None | Line voltage too low or too high | Yes |
| 87 | 4 flashes | Flame rollout switch open | Yes |
| 88 | 6 flashes | No proper earth ground detected | Yes |
| 90, 91 | 10 flashes | Communication busy or failed between the board, blower, inducer and thermostat | Yes |
| 92 | None | 24-volt fuse open | Yes |
| 93 | 7 flashes or solid on | Gas valve fault | Yes |
| 101 | None | Y1 relay failure | Yes |
| 114 | None | Bad or missing personality module | Yes |
| 119 | None | Temperature sensor failure | Yes |
| 139 | 10 flashes | Communication message seen while set up for 24-volt mode | Yes |
For 26, replace a dirty filter first. For a lockout, the same guide says the system can be reset by turning the system power off. On power-up, the red LED flashes the last 4 alerts, newest first, with a 2-second gap between them.
XV18 outdoor unit alert codes
The XV18 is a communicating variable-speed system. Trane's tax-credit certificate lists the XV18 air conditioner as the 4TTV8 and the heat pump as the 4TWV8. The 4TTV8X and 4TWV8X service facts (4T-V8X-SF-1C-EN, pages 21 to 33) list these alert codes, which the unit sends to the thermostat. All of them are technician work. For the XV18 itself, see our Trane XV18 review.
| Alert code | What it means | What you can check | Call a pro? |
|---|---|---|---|
| 18 | Internal control failure | Nothing | Yes |
| 67 | Temperature sensor fault (ambient, coil, discharge or suction) | Nothing | Yes |
| 68 | Defrost fault (heat pumps) | Nothing | Yes |
| 80 | High pressure switch tripped; runs at reduced capacity or locks out | Nothing | Yes |
| 88 | Ground fault at the compressor drive | Nothing | Yes |
| 90, 91, 94 | Communication busy, lost or a device missing | Nothing | Yes |
| 106 | External shutdown or indoor external switch open | Nothing | Yes |
| 114 | Bad or missing personality module | Nothing | Yes |
| 155, 164 | Expansion valve motor fault, or valve stuck open | Nothing | Yes |
| 156, 165, 166 | Low charge, or superheat too high or too low | Nothing | Yes |
| 159, 172 | Service display fault or stuck key | Nothing | Yes |
| 174, 175 | Suction pressure sensor fault, out of range, or limp-along mode | Nothing | Yes |
| 176 to 186 | Compressor drive faults: communication, current, voltage, temperature, start-up, shutdown and protection | Nothing | Yes |
| 187 | Evacuation or drive diagnostics mode left on | Nothing | Yes |
| 188, 189 | Internal storage, configuration or voltage error; board too hot | Nothing | Yes |
| 191 | Outdoor fan motor lost a phase | Nothing | Yes |
Rows that share a cell group codes the guide lists one by one with the same kind of cause. The newer R-454B XV18 air conditioner (5TTV8X) runs only on Trane Link with a UX360 thermostat, according to its own service facts, which carry a separate alert list we have not transcribed here.
Models this covers
- S9X1, S9X2, S9B1 gas furnaces: display code table (18-CE12D1-1D-EN).
- S8X1, S8X2, S8B1 gas furnaces: same table without E09 (18-CE16D1-1C-EN).
- *UH1 and *DH1 condensing furnaces, Trane or American Standard: flash code table (18-CD29D1-14-EN).
- *UHM and *DHM modulating communicating furnaces: alert code table (18-CD30D1-20-EN).
- ComfortLink II XL1050 thermostat: alert format and severity (18-HD80D1-6F-EN, 32-5093-04B-EN).
- XV18 4TTV8X and 4TWV8X outdoor units: alert codes (4T-V8X-SF-1C-EN).
The S9V2 variable-speed furnace guide we opened shows status codes but prints no fault list, so S9V2 codes are not here. We did not find an XV20i document. If your furnace won't start and shows nothing, work through our furnace won't turn on checklist. If it runs but blows cold, see why a furnace blows cold air. Other brands: Carrier furnace codes, Goodman furnace error codes and Lennox furnace error codes.
Trane's lockout page says furnace troubleshooting is best left to an HVAC professional. Give the technician the code, the model number and what the system does when the thermostat calls for heat. Our find an HVAC technician page can match you with one nearby.
Frequently asked questions
How do I reset a Trane furnace error code?
For Trane and American Standard *UH1 and *DH1 furnaces, the installer's guide says to turn the power off, on, off and on again within 30 seconds, at the furnace power source or the thermostat. S-series furnaces retry on their own after a one-hour lockout. Reset once. Trane says repeated stops become a hard lockout that a technician must reset after finding the cause.
What does E2.1 mean on a Trane furnace?
On S9X1, S9X2, S9B1 and S8-series furnaces, E2.1 means retries exceeded: the furnace tried to light 3 times and never sensed a flame, so it locked out for one hour. Check that the thermostat is on Heat and set above room temperature. If E2.1 comes back, the igniter, gas supply or flame sensor needs a technician.
What do 4 flashes mean on a Trane furnace?
On the *UH1 and *DH1 furnaces, 4 flashes means an open high limit: the furnace got too hot and a safety switch shut the burners off. Low airflow is the common cause, so replace a dirty filter and keep return vents clear. On communicating furnaces, 4 flashes can also mean an open flame rollout switch, which needs a technician.
Are Trane and American Standard furnace codes the same?
On the furnaces we checked, yes. Trane's installer's guides for the *UH1, *DH1, *UHM and *DHM furnaces say the first letter of the model number may be A or T, meaning one guide and one code table covers both brands. The S-series guides are also published for both Trane and American Standard. Check your model number against the guide.
What does Err 126 mean on my Trane thermostat?
Trane's XL1050 installation guide lists Err.126.00 as the outdoor unit not reporting to the thermostat. The usual sign is a heat pump that won't run while only the furnace or electric heat strips come on. It points at communication with the outdoor unit, so a technician needs to check its wiring and status.
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