Trane thermostats are popular for their smart monitoring of homeowner’s HVAC systems. This monitoring includes safety features that keep your home and equipment from experiencing costly or hazardous damage.
Trane thermostats have a variety of error codes to help address any issues with the HVAC system. Most commonly, issues that occur are related to low-pressure, extreme temperatures, faulty sensors, and power or WiFI interruptions. In many cases, the system simply needs to be reset or a sensor needs replacement.
This article goes on to list Trane thermostat safety feature error codes that a homeowner may see on various models. The most common error codes are included along with ways to address them on your own or with the help of a professional.
List of Trane Error Codes
Trane thermostats are designed to tell you if there is a problem with the thermostat or the HVAC system.
The error code will appear on the thermostat’s display in the corner of the screen, at the bottom, or alternating with the time.
Codes may differ depending on the model of the Trane thermostat you own. The code may appear as 2 or 3 digits or have the letter “E” (for “error”) with a digit.
The following table offers a general list of error codes that appear on various Trane thermostats along with what they mean:
| Error Code | What It Means |
| E0 | Thermistor (temperature sensor) cannot read an extreme temperature that is less than 14°F or greater than 122°F |
| E1 or flashing “-” | Communication issue between mini split in the outdoor and indoor unit’s humidity sensor |
| E2 | Return temperature sensor is not communicating with the network |
| E3 | Low-pressure protection |
| E4 | Input voltage is not in range (lower than 18 VAC or greater than 32 VAC) |
| E5 | Error with the Room Thermostat Controller (RTC) |
| E6 | Communication failure between outdoor and indoor chips due to wiring or main control board |
| E7 | Heating fan fault due to |
| E8 | Fan speed malfunction |
| 22 | Soft lockout due to flame loss or unsuccessful ignition |
| 26 | Furnace is overheating or exceeded set temperature limit |
| 67.06 | Suction temperature sensor is not working in cooling mode |
| 79 | Low-pressure switch is open; hard lockout |
| 89 | Cannot find HVAC equipment due to blown fuse or wiring issue |
| 90 | Device does not recognize equipment |
| 91 | Communication failure between thermostat and HVAC equipment |
| 126 | Communication failure between thermostat and HVAC equipment or low-temperature lockout |
| 158 | Evaporator coil is too cold (below 32°F) |
| 184 08 | System is shutdown; soft lockout |
| Err (with a red light) | Refer to user guide or contact customer support |
Your Trane user guide can assist you with identifying what the code means on your particular thermostat as well.
Knowing what the problem is can help you remedy the issue, possibly preventing the need for an expensive service call.
The remainder of this article will address the most commonly appearing error codes and what you can do to fix them.
What is Error 79 on a Trane Thermostat?
Error code 79 means that the low-pressure switch is open, and the system is on a hard lockout.
Pressure switches open and close when pressure is applied to the diaphragm of the switch.
The low-pressure switch senses excessively low suction pressure, and high-pressure switches sense excessive discharge pressure. These are safety features to prevent unsafe operation of your HVAC system.
The causes of an open low-pressure switch can be the following:
- Low batteries
- Dirty thermostat sensors
- Defective low-pressure switch
- Iced evaporator coil
- Clogged air filter
- Low refrigerant
How To Address Error 79
If you find that the evaporator coil is iced despite the remedies below or you have low refrigerant, contact a professional to further assist you.
Reset The Thermostat
Hard lockout occurs when the HVAC system has made and failed three attempts to restart. When a hard lockout happens, the system needs to be manually reset.
Resetting a Trane thermostat is the first thing to try when addressing error 79. The steps to do this can vary depending on the model of the thermostat you have.
What to do:
- Before rebooting the system, turn off the power to both the inside and outside units.
- Hold down the minus (-) and plus (+) buttons together for 4 seconds.
- Or, the model may have a “reset” button that you can press instead.
- Wireless models typically have a menu you can scroll to find “reboot” in the settings.
- Restore power to the units.
- Wait 30 minutes, and then turn on the thermostat to activate the system.
Other Quick Remedies
If error code 79 persists, try the following strategies next:
- Change the batteries.
- Clean the thermostat’s internal sensors. Use compressed air or a clean, soft paintbrush to eliminate dust and debris.
- Replace the filter.
Replace The Low-Pressure Switch
In most cases, the system simply needs a reset or clean filter, or the thermostat needs fresh batteries or cleaning.
The next common issue is the need to replace the low-pressure switch.
Do the following to replace the low-pressure switch:
- Find your user guide to locate this part and turn off all power to your HVAC system.
- Remove the switch by disconnecting the negative battery cable and the switch’s electrical connector. The switch typically unscrews out once disconnected.
- Install the new switch, ensuring that it is snugly screwed in and attached to the cable and connector.
- Turn the power back on and test the system.
What does Trane Error 91 mean?
Trane error code 91 means that there is a communication failure between the thermostat and the HVAC equipment.
Typically this is due to an issue with a lack of power from the low-voltage line from the furnace. These can stem from power glitches or surges.
How To Address Error 91
Most of the time the thermostat will pick the signal back up and restart on its own. This typically takes 10 minutes or less. If not, try the reset procedure mentioned above.
If the error remains on for more than 30 minutes, you may need a new thermostat or circuit board.
Contact your HVAC professional to check out the power sources for your furnace and install new parts. If your furnace is under warranty you may not have to pay for these.
If power issues continue, contact your local utility provider to see if there is an issue with the main power line that comes to your home.
What is Error 126 on the Trane Thermostat?
Error code 126 means that there is a communication failure between the thermostat and the HVAC equipment or there’s a low-temperature lockout.
The following are the most common reasons why this error occurs:
- The furnace or air conditioner is not responding to the thermostat.
- A power surge caused the thermostat to stop communicating.
- The high-voltage fuse is blown.
- The outdoor transformer is not working.
- There is a broken or loose wire in the system’s circuitry.
- Lockout occurred due to low evaporator pressure or refrigerant.
How To Address Error 126
First, turn off the HVAC system and wait for 5 to 10 minutes. Turn it back on and see if the error notification goes away.
If this does not work, turn off the power to your HVAC system again, and try the following:
- Reset the system (described above).
- Replace any blown fuses in the circuit board.
- Check wire connections and replace any bad ones.
- Contact your utility company if power surges are coming from the main line.
- Contact an HVAC expert to remedy any serious electrical issues or place parts that affect temperature monitoring.
What is Error 158 on the Trane Thermostat?
Error 158 on the Trane thermostat means the evaporator coil is too cold. It has been below 32°F for at least 20 minutes.
The system will not turn on to prevent the unit from freezing up. It may turn back on automatically if the coil’s temperature warms up over 32°F.
Typically, this error occurs when there is low airflow or low refrigerant. If it is not addressed, it can cause costly damage to the system’s compressor.
How To Address Error 158
Replace the filter with a new, clean one. If this does not resolve the issue, contact your HVAC professional to address low refrigerant.
What Does Error E1 Mean on the Trane Mini Split?
Error E1 on the Trane mini split means there is a communication issue between the mini split and the unit’s humidity sensor. Instead of error E1, there may be a flashing dashed line (-) in the display.
This is typically due to a blown fuse, a humidity reading outside of the measurable range, or a faulty humidity sensor.
How To Address Error E1
First, reset the system as described above. If that does not resolve the issue, turn off the power and check the connections to the humidity sensor.
If the connections are not the problem, replace the humidity sensor.
What is Error E2 on the Trane Thermostat?
Error E2 means the return temperature sensor is not communicating with the network.
In most cases either the sensor is faulty or your WiFi network has a connectivity issue.
How To Address Error E2
Check your home’s internet connection and router to make sure they are working and connected. If the WiFi has gone offline, once it is back online, the thermostat should automatically reconnect.
If not, refer to your user guide on how to connect your thermostat to your WiFi system.
If this does not resolve the issue, then the sensor or thermostat will need to be replaced.
What Does Error E4 Mean On A Trane Thermostat?
Error E4 means that the input voltage is not in range. This indicates the input voltage is lower than 18 volts of alternating current (VAC) or greater than 32 VAC.
How To Address Error E4
If you are unsure about how to deal with electrical currents, please refer this kind of work to a professional.
The voltage of the common C-wire can be checked with a multimeter tool.
If the multimeter shows that the voltage is out of range, then the wire needs to be replaced. If the voltage is fine, then it is likely that the thermostat needs to be replaced.
Conclusion
In many cases, resetting the HVAC system will clear error codes on a Trane thermostat. Electrical error codes are typically related to power issues such as glitches, surges, poor batteries, or blown fuses.
Dirty filters, dusty internal components on the thermostat, and faulty sensors can also cause error codes to appear.
When working with electrical components, make sure that the entire HVAC system is off. Contact professional HVAC installers to address wiring, circuit board, or low-refrigerant issues.
Whether it is furnace error codes or ones for your Trane thermostat, rest assured that we have you covered.
Ruben has a diverse background in the home services industry, with experience running a construction company, a kitchen and bath showroom, and a moving and relocation company. This breadth of experience has provided him with a wealth of knowledge and expertise in various areas of home improvement in general and specifically in the heating and plumbing niche.