Trane HVAC Error Code 25: How to Fix It
Medium 30–60 minutes Medium Severity
Verified June 2026
- Error Code
- 25
- Brand
- Trane
- Product Type
- hvac
- Severity
- Medium
- DIY Difficulty
- Medium
- Estimated Fix Time
- 30–60 minutes
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Tools You'll Need
- Phillips screwdriver
- Flathead screwdriver
- Multimeter (digital, capable of AC voltage and continuity testing)
- Non-contact voltage tester
- Flashlight or work light
- Needle-nose pliers
How to Fix Error Code 25
-
Turn Off the System at the Thermostat
Never attempt to inspect or service HVAC electrical components while the system is actively running. Always power down from the thermostat first. -
Check and Reset the Circuit Breaker
A breaker that trips repeatedly is a sign of a serious electrical problem. Do not keep resetting it, as this can cause overheating or fire. -
Inspect the Indoor Unit Disconnect Switch
Turn off the circuit breaker at the main panel BEFORE touching the disconnect box to avoid electric shock. -
Inspect the Control Board Transformer
Working inside the air handler with power on is dangerous. If you are not comfortable using a multimeter around live wiring, stop here and call a licensed HVAC technician. -
Check All Wiring Connections at the Control Board
Confirm power is OFF at both the circuit breaker and the local disconnect before touching any wiring inside the unit. -
Inspect the Control Board for Damage
Do not attempt to power on a unit with a visibly damaged control board, as this can cause further damage or create a fire hazard. -
Clear the Error and Test the System
If error code 25 returns after completing all steps, do not continue attempting DIY repairs. Contact a licensed HVAC technician for further diagnosis.
Parts You May Need
HVAC Control Transformer (24V)
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Air Handler / Furnace Control Board
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Disconnect Box Fuses
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Low-Voltage Thermostat Wire
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HVAC Control Transformer (24V)
Check Price on Amazon
Air Handler / Furnace Control Board
Check Price on Amazon
Disconnect Box Fuses
Check Price on Amazon
Low-Voltage Thermostat Wire
Check Price on Amazon
HVAC Control Transformer (24V)
Check Price on Amazon
Air Handler / Furnace Control Board
Check Price on Amazon
Disconnect Box Fuses
Check Price on Amazon
Low-Voltage Thermostat Wire
Check Price on Amazon
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When to Call a Professional
You should call a licensed HVAC technician if: the circuit breaker trips repeatedly after being reset; you measure no output voltage from the transformer but are unsure how to safely replace it; you find visible burn damage on the control board, wiring, or transformer; you are uncomfortable working around live 120V or 240V electrical components; or if error code 25 persists after completing all troubleshooting steps. Power supply faults that involve the main line voltage side of the system (above 24V) should always be handled by a certified professional to ensure safety and code compliance.Frequently Asked Questions
What does Trane error code 25 mean?
Trane error code 25 indicates a power supply fault in the indoor HVAC unit. This means the system has detected an abnormal electrical condition, such as low voltage, a failed transformer, a tripped breaker, or a loose wiring connection that is preventing the indoor unit from operating correctly.
Can I fix Trane error code 25 myself?
Some causes of error code 25 — like a tripped circuit breaker or a loose low-voltage wire — are straightforward DIY fixes. However, if the fault involves a failed transformer, damaged control board, or a problem with the main line voltage supply, it is strongly recommended that you call a licensed HVAC technician for safe and proper repair.
How much does it cost to fix a Trane HVAC power supply fault?
Costs vary depending on the cause. Resetting a tripped breaker is free. Replacing a 24V control transformer typically costs $50–$150 for parts plus 1–2 hours of labor. Replacing a control board can range from $150–$600 or more depending on the model. Always get a written estimate from a licensed technician before authorizing repairs.
Why does my Trane HVAC keep showing error code 25?
If error code 25 keeps returning after being cleared, it usually points to an underlying issue that has not been fully resolved — such as an intermittently failing transformer, a wiring short, a failing control board, or an overloaded electrical circuit. Persistent faults require a thorough diagnostic by a licensed HVAC technician.
Is it safe to run my Trane HVAC with error code 25?
No. When error code 25 is active, the system is detecting a power supply fault and may not operate safely or reliably. Continuing to attempt to run the system can cause further damage to the control board, transformer, or other components. Shut the system down until the fault is diagnosed and resolved.