Decoding Trane Thermostat Error Codes: A Complete Troubleshooting Guide

Having an issue with your Trane thermostat displaying an error code? Don’t worry – this guide will walk you through how to diagnose and resolve many common Trane thermostat error codes.

As one of the leading manufacturers of HVAC systems, Trane thermostats are highly advanced devices that rely on a network of sensors to precisely regulate temperature. While this provides superior climate control, it also means there are more potential points of failure.

Fortunately, Trane thermostats have built-in self-diagnostics that generate error codes when they detect a problem. Understanding what these codes mean is key to pinpointing and correcting the issue.

In this comprehensive guide, we’ll provide an overview of Trane thermostat error codes and provide actionable steps to get your system up and running again.

A Quick Primer on Trane Thermostat Error Codes

Trane thermostats display issues and faults as either numeric error codes or brief text-based messages. Here’s a quick introduction to how Trane error codes work:

  • Numeric error codes – These 2-3 digit codes indicate specific issues detected by the thermostat. Each code corresponds to a particular fault condition.
  • Text error messages – Some Trane models use simple words like “Error” or “Fault” along with a cryptic 2-letter code like “EA”. These point to general problems.
  • LED light indicators – On some Trane thermostat models, an LED may also flash a certain color or pattern to reflect an error.
  • Error log – Most Trane thermostats keep a record of the last few errors. You can review these in the thermostat system menu.

Now let’s explore some of the most common Trane thermostat error codes and messages, and how to troubleshoot them.

Trane Thermostat Numeric Error Codes

trane thermostat numeric error codes
Trane Thermostat Numeric Error Codes

Here are the numeric error codes seen on XL8 and XL10 Trane thermostats and their meanings:

Error Code 01 – Internal Thermostat Fault

This rather generic code indicates an internal problem with the thermostat control board. Some potential causes include:

  • Corrupted firmware
  • Bad processor
  • Memory failure

Troubleshooting Tips:

  • Try rebooting the thermostat by cutting power for 10-15 seconds. This may clear any temporary glitches.
  • If the error persists, you’ll likely need to replace the thermostat control board. Contact a technician.

Error Code 03 – Stuck Relay

This simply means one of the internal relays on the thermostat control board is stuck in the closed or open position. This prevents proper operation.

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  • First, reboot the thermostat. The relay may just be momentarily jammed.
  • If code 03 returns, you’ll need to replace the thermostat control board. A professional should handle this repair.

Error Code 12 – Loss of Communication with Outdoor Unit

This code indicates the thermostat is unable to communicate with the condenser or heat pump outside your home. Some potential causes are:

  • Faulty wiring between thermostat and outdoor unit
  • Bad circuit board on outdoor unit
  • Failed wireless communication module


  • Verify wiring between indoor and outdoor units is intact and securely connected
  • Check for loose wiring splices or shorts
  • Inspect outdoor unit control board for signs of damage or burnt components
  • If wireless, check that antenna is upright and undamaged

Error Code 13 – Incompatible Equipment

This simply means the thermostat has detected connected equipment that it cannot communicate properly with. For example:

  • Older equipment lacking data terminals
  • Wrong model outdoor unit
  • Aftermarket parts mixed with original Trane gear


  • Verify model numbers and compatibilities of all connected components
  • Swap out non-compatible parts for officially supported Trane equipment
  • You may need to install an older, less advanced thermostat

Error Code 14 – Thermostat Sensing Failure

This code indicates the thermostat’s internal sensors are damaged or malfunctioning. It can no longer accurately read temperature or humidity.


  • Inspect thermostat housing for damage or visible issues
  • Look for detach/broken sensor wires inside the unit
  • Test sensors using a multi-meter and compare to room conditions
  • If sensors are defective, replace the thermostat control board

Error Code 15 – Heat Pump Reversing Valve Failure

This code means the thermostat detected an issue with the reversing valve in your heat pump system. Potential causes include:

  • Reversing valve stuck in cooling or heating mode
  • Faulty solenoid coil
  • Low refrigerant pressure
  • Wiring problems


  • Verify refrigerant charge – recharge if low
  • Check wiring to reversing valve for continuity
  • Listen for audible click when it switches modes
  • Replace faulty reversing valve or coil as needed

Error Code 16 – Defective Compressor Contactor

This means the contactor (relay) that engages the compressor is not working properly. Issues include:

  • Contactor not pulling in
  • Welded contacts
  • Open coil


  • Verify contactor is receiving voltage during operation
  • Check contacts for pitting or signs of melting/welding
  • Test coil resistance and replace if open/shorted
  • Replace faulty contactor if needed

Error Code 17 – Anti-Short Cycle Timer Lockout

This indicates the AC system turned on and off too quickly, causing the thermostat to lock it out temporarily to prevent equipment damage. Causes include:

  • Insufficient air flow due to soily filters/coils
  • Overcharged refrigerant system
  • Faulty thermostat contacts


  • Clean filters, blower assembly, and condensing coil
  • Check refrigerant charge and adjust as needed
  • Verify proper air flow across evaporator
  • Replace thermostat if contacts are damaged

Error Code 21 – Defrost Control Board Failure

This code indicates a problem with the defrost control board on a heat pump system. Issues include:

  • Defrost sensor damaged
  • Defrost control circuitry malfunction
  • Bad defrost board


  • Check continuity of defrost temp sensor bulb and capillary
  • Inspect defrost board for signs of damage
  • Verify defrost terminations are properly spaced
  • Replace defrost control board if faulty

Error Code 22 – Maximum Defrosts Exceeded

This means the heat pump system is repeatedly going into defrost mode due to an underlying problem. Potential causes:

  • Low refrigerant charge
  • Defrost sensor not reading properly
  • Too much frost buildup on coils


  • Check refrigerant level and recharge if low
  • Replace thermistor if not reading properly
  • Check door/window seals and add weather stripping as needed
  • Repair any issues causing excessive frosting

Error Code 23 – Secondary Voltage Overload

This indicates excessive current on the secondary winding in the outdoor unit’s transformer. Potential causes include:

  • Short circuit in outdoor unit wiring
  • Grounded compressor windings
  • Faulty transformer
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  • Check for wiring faults and shorts in outdoor unit
  • Test compressor windings for grounds
  • Verify transformer secondary voltage
  • Replace transformer if faulty

Error Code 24 – Secondary Voltage Dropout

This means there was a loss of the 24VAC control voltage in the system. Typical causes:

  • Transformer failure
  • Loose wiring connections
  • Blown low voltage fuse
  • Faulty control board


  • Check transformer secondary voltage and replace if faulty
  • Verify tight and secure low voltage connections
  • Inspect low voltage fuse and replace if blown
  • Test control board voltages and replace if faulty

Error Code 31 – Faulty Pressure Sensor

This code indicates an issue with the pressure transducers inside the outdoor unit. Problems include:

  • Sensor not reading properly
  • Sensor damaged or unplugged
  • Faulty sensor wiring


  • Check sensor electrical connections
  • Verify pressure readings with gauges on service ports
  • Replace pressure sensor if damaged or reading incorrectly

Error Code 32 – Pressure Trip Due to Frozen Coil

This means high pressure cutout occurred because of frozen evaporator coils. Some potential causes are:

  • Very low outdoor ambient temperature
  • Insufficient airflow over coils
  • Possible refrigerant undercharge


  • Check blower assembly and air filter for blockages
  • Verify proper airflow across coils
  • Monitor refrigerant pressures
  • Charge system properly if low on refrigerant

Error Code 33 – Pressure Trip Due to High Ambient Temperature

This code indicates the high pressure safety switch opened due to excessive ambient temperatures. This commonly occurs during summer peaks.


  • No action needed; resumes operation on its own
  • If frequent, check refrigerant charge and blower assembly

Error Code 34 – Pressure Trip Due to Lazy Compressor

This means the high pressure safety activated because the compressor is not building enough pressure. Causes include:

  • Bad compressor valves
  • Slugging reciprocating compressor
  • Faulty rotary/scroll compressor


  • Test compressor pressures and temperatures
  • Check compressor amp draw for issues
  • Verify proper capacitor value for compressor
  • Replace compressor if faulty or damaged

Error Code 35 – Discharge Temperature Too High

This code means the discharge line temperature sensor exceeded safe limits for the compressor. Potential causes:

  • Overcharged refrigerant system
  • Dirty condenser coils
  • Non-condensibles in system
  • Bad discharge sensor


  • Check refrigerant charge and remove excess
  • Clean debris from condenser coil
  • Reclaim and recharge refrigerant to remove air
  • Verify discharge sensor resistance/continuity

Error Code 41 – Defective Outdoor Air Temp Sensor

This code signifies the outdoor temperature sensor is damaged or malfunctioning. Problems include:

  • Bad thermistor
  • Sensor disconnected
  • Shorted/open sensor wiring


  • Check sensor wiring for damage
  • Verify ohms reading on thermistor
  • Replace outdoor temperature sensor

Error Code 42 – Defrost Temp Sensor Abnormal

This means the defrost temperature sensor is not reading properly. Issues include:

  • Sensor disconnected
  • Shorted/damaged capillary
  • Failed sensing element


  • Verify sensor is firmly attached to coil tubing
  • Check capillary continuity
  • Replace defrost temp sensor

Error Code 43 – Suction Temp Sensor Abnormal

This error points to problems with the suction line temperature sensor including:

  • Disconnected sensor
  • Shorted/open wiring
  • Failed sensing element


  • Check sensor is properly installed and connected
  • Verify wiring for damage and shorts
  • Test sensor resistance and compare to temperature
  • Replace sensor if faulty

This covers the most common Trane thermostat numeric error codes. Refer to your model’s service manual for any other codes not listed here.

Now let’s look at some typical text error messages and how to address them.

Trane Thermostat Text Error Codes

Here are some text-based error messages seen on Nexia and other newer Trane thermostats:

EA Error Code

The simple “EA” error code indicates a problem with the control board memory. Causes can include:

  • Corrupted firmware
  • Faulty memory chip
  • Voltage spike/surge damage
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  • Reboot the thermostat and reset to factory defaults if possible
  • Upgrade to latest firmware version if available
  • Replace control board if error persists

EF Error Message

The “EF” code signifies an issue with the internal thermostat fan. Potential causes are:

  • Blocked fan
  • Faulty blower motor
  • Disconnected fan wiring


  • Remove any obstructions and verify fan spins freely
  • Check blower motor windings for continuity
  • Verify tight blower motor wiring connections
  • Replace blower motor if defective

Er Error Code

A simple “Er” error means there is an issue with the thermostat hardware. This could indicate:

  • Damaged display
  • Faulty control board
  • Loose internal wiring


  • Verify all internal wire connections are secure
  • Check for visible damage to thermostat internals
  • Replace control board or entire thermostat if faulty

E1 or E2 Error Code

E1 or E2 errors indicate a problem with the outdoor condenser unit. Specific issues include:

  • Faulty outdoor control board
  • Bad condenser fan motor
  • Compressor contactor not engaging


  • Check condenser control board for damage
  • Verify tight wiring connections
  • Test condenser fan motor for functionality
  • Inspect compressor contactor and replace if needed

Hopefully this gives you a better understanding of common Trane thermostat error codes. While intimidating at first, troubleshooting them simply involves systematically isolating the faulty component based on the code.

Troubleshooting Strategies for Trane Thermostat Problems

Beyond decoding error codes, there are also some general best practices you can follow to diagnose and fix issues with your Trane thermostat:

Check error logs – Most Trane thermostats record fault history, accessible through the service menus. Look for any consistent or recurring error codes to help identify the underlying problem.

Rule out power issues – Use a multimeter to check for 24VAC at the thermostat wiring terminals, and 120VAC at the system equipment. Power-related errors can mimic other faults.

Inspect connections – Remove and re-seat electrical connectors between the thermostat and HVAC components. Check for pinched, loose, or damaged wires.

Cycle the power – A power reset can clear transient electrical and firmware glitches causing erratic behavior. Turn off the power at the breaker for 10-15 minutes before restoring it.

Update firmware – Download and install the latest software and firmware revisions from Trane’s website. Outdated code can cause bugs.

Test individual parts – Check thermostat sensors, system relays, motors and other components with a multimeter to isolate failures. Replace defective parts.

Watch for patterns – If an issue seems to occur at a particular time of day or under specific conditions, it can indicate certain causes. Take notes.

Consult technical resources – Trane provides extensive thermostat troubleshooting advice in service manuals available online or from local dealers.

Following logical diagnostic steps and consulting factory documentation can help identify most Trane thermostat issues. But for complex electrical or refrigeration problems, don’t hesitate to enlist the aid of an HVAC technician.

When to Call in a Professional for Your Trane Thermostat

when to call in a professional for your trane thermostat
When to Call in a Professional for Your Trane Thermostat

While DIY troubleshooting can resolve many basic Trane thermostat errors, it’s reasonable to call in a professional HVAC technician for assistance in some situations:

  • If the repair requires accessing internal components for testing or replacement
  • For pervasive electrical problems across multiple system components
  • If system pressures or temperatures exceed safe levels during testing
  • When dealing with refrigerant system leaks or recharging issues
  • For any major system repairs such as replacing a compressor or fan motor
  • If errors persist despite your best troubleshooting efforts

There are some circumstances where even simple repairs can carry safety risks or void equipment warranties if handled improperly. Trane dealership technicians have the specialized skills, experience, and tools to accurately diagnose and fix complex HVAC problems. Investing in professional service also helps ensure any warranty coverage remains intact.

Preventing Future Trane Thermostat Trouble

While even well-maintained Trane equipment is subject to occasional issues, there are some steps you can take to help avoid thermostat malfunctions in the future:

  • Install firmware updates for the thermostat whenever available
  • Use a surge protector to prevent electrical damage during storms
  • Limit exposure to dust and debris which can cause problems
  • Keep the thermostat away from excess humidity and heat sources
  • Adjust schedule and settings to avoid rapid cycling or excessive run times
  • Have yearly maintenance done by an HVAC professional

Following the operating guidelines in your Trane thermostat user manual can also minimize avoidable problems over time. Simple preventive care goes a long way towards ensuring your system stays up and running.

Get Your Trane System Back to Providing Comfort and Efficiency

Trane produces some of the finest air conditioning systems and thermostats, but even premium products require troubleshooting and repairs occasionally. With the tips in this guide, you can confidently decode the most common Trane thermostat error codes and restore normal operation.

But when more advanced diagnostics or repairs are needed, don’t hesitate to enlist the help of a professional Trane service technician. The cost of an expert repair is minor compared to the extended comfort and functionality you’ll regain. Get your Trane system back up and running so your home or office can stay cool during the sweltering summer ahead!

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