Trane Furnace & AC Error Codes

Below is a complete list of Trane furnace and air conditioner diagnostic error codes (also applies to American Standard). Each code includes what it means, safe DIY checks you can try, when to call a professional, and estimated repair costs.

How to Read Trane Error Codes

Look through the sight glass on the furnace access panel to see the diagnostic LED. Count the number of times the LED blinks before it pauses, then repeats. A slow steady flash means normal standby. A fast steady flash means normal operation with a call for heat. A specific number of blinks followed by a pause indicates an error code.

LED Location: Visible through the sight glass on the lower front access panel. The LED is located on the integrated furnace control board.

Code Format: Single-digit flash code: count the number of LED flashes in each repeating sequence (e.g., 3 flashes, pause, 3 flashes = Code 3)

Safety Warning

1 emergency code(s) require immediate professional attention. 6 high-urgency code(s) should be addressed promptly. If you smell gas, hear unusual sounds, or see sparks, turn off the system and call a professional immediately.

Quick Navigation — 12 Error Codes

Slow Flash (1 blink/sec) Fast Flash (rapid blinking) LED On Continuously (not flashing) 2 Flashes 3 Flashes 4 Flashes 5 Flashes 6 Flashes 7 Flashes 8 Flashes 9 Flashes LED Off (no light)

Trane Slow Flash (1 blink/sec): Normal operation — no call for heat

Low Urgency

The furnace is powered on and operating normally. It is in standby mode waiting for the thermostat to call for heat. This is the expected status when the furnace is idle.

Common Causes

  • Thermostat is not calling for heat (normal condition)
  • Temperature in the home is at or above the set point

DIY Troubleshooting Steps

  1. This is normal — no action needed if you do not need heat at this time
  2. If you expect the furnace to be heating, check that your thermostat is set to HEAT and the set temperature is above the current room temperature

Call a professional when: The furnace shows this status but does not respond when the thermostat calls for heat.

Trane Fast Flash (rapid blinking): Normal operation — call for heat active

Low Urgency

The furnace is powered on and actively responding to a call for heat from the thermostat. This is the normal operating status during a heating cycle.

Common Causes

  • Thermostat is actively calling for heat (normal condition)
  • Heating cycle is in progress

DIY Troubleshooting Steps

  1. This is normal — the furnace is heating as expected
  2. If the furnace is blinking fast but you feel no warm air from the vents, the heating cycle may just be starting (allow 2-3 minutes)

Call a professional when: The LED flashes fast but the furnace does not produce heat after 5 minutes, or you hear unusual sounds.

Trane LED On Continuously (not flashing): Control board failure

High Urgency

The LED is on solid without blinking, indicating the control board has an internal failure and is not running its diagnostic cycle properly.

Estimated repair cost: $400 – $1,200

Common Causes

  • Defective control board (failed microprocessor)
  • Power surge or lightning damage to the board
  • Age-related failure of board components

DIY Troubleshooting Steps

  1. Try resetting the furnace by turning the power off for 60 seconds, then back on
  2. Check for visible burn marks or melted components on the control board (turn off power first)

Call a professional when: The LED remains solid after a power reset. The control board likely needs replacement, which must be done by a technician.

Trane 2 Flashes: System lockout — retries or recycles exceeded

High Urgency

The furnace has entered a lockout after exhausting its allowed number of ignition retries or operating recycles. The system detected repeated failures and shut down for safety. A manual reset is typically required.

Estimated repair cost: $100 – $400

Common Causes

  • Dirty or faulty flame sensor not detecting the flame
  • Weak or failed hot surface igniter
  • Gas supply interruption or low gas pressure
  • Clogged pilot tube (on older models with pilot lights)

DIY Troubleshooting Steps

  1. Reset the furnace by turning power off for 30 seconds, then back on
  2. Clean the flame sensor with fine steel wool or emery cloth (turn off power first)
  3. Verify gas supply is on and other gas appliances in the home work

Call a professional when: The lockout occurs again after reset and flame sensor cleaning. A technician can test igniter resistance, flame sensor microamp reading, and gas pressure to find the root cause.

Trane 3 Flashes: Vent pressure switch error

Medium Urgency

The pressure switch that monitors proper venting of combustion gases has failed to close or has opened during operation. This safety device ensures exhaust gases are being properly vented out of the home.

Estimated repair cost: $150 – $500

Common Causes

  • Blocked exhaust vent or intake pipe (ice, debris, bird nests)
  • Clogged condensate drain line causing water backup (on 90%+ efficiency models)
  • Failed or weak inducer motor not creating enough draft
  • Cracked, kinked, or disconnected pressure switch hose

DIY Troubleshooting Steps

  1. Check the exhaust and intake pipes outside your home for blockages — clear any ice, snow, leaves, or debris
  2. On high-efficiency furnaces, check the condensate drain and trap for clogs — pour warm water through the drain line
  3. Inspect the small rubber hose connected to the pressure switch for cracks, kinks, or moisture

Call a professional when: The vents are clear and drain is flowing but the code persists. The inducer motor may be failing, the pressure switch may need replacement, or there could be a heat exchanger issue.

Trane 4 Flashes: Open high-temperature limit device

High Urgency

The high-temperature limit switch has opened, indicating the furnace is overheating. This safety device shuts down the burners to prevent heat exchanger damage and fire hazard. The furnace is not getting adequate airflow across the heat exchanger.

Estimated repair cost: $150 – $600

Common Causes

  • Dirty or clogged air filter (most common cause of overheating)
  • Blocked or closed supply/return air registers
  • Failed blower motor or bad run capacitor
  • Dirty blower wheel reducing airflow

DIY Troubleshooting Steps

  1. Replace the air filter immediately — this is the most common cause
  2. Make sure all supply and return vents/registers throughout your home are open and not blocked by furniture, curtains, or rugs
  3. Listen for the blower fan — if it is not running or sounds weak, the motor or capacitor may need attention

Call a professional when: The code returns after changing the filter and opening all vents. This may indicate a failing blower motor, bad capacitor, dirty blower wheel, or a more serious heat exchanger issue.

Trane 5 Flashes: Flame sensed when no flame should be present

Emergency

The flame sensor is detecting a flame signal even though the gas valve is commanded off and no flame should exist. This is a potentially dangerous condition indicating gas may be leaking past the gas valve.

Estimated repair cost: $200 – $650

Common Causes

  • Leaking gas valve allowing gas to flow when closed
  • Gas valve stuck in the open position
  • Defective flame sensor providing false readings
  • Residual flame or heat near the sensor

DIY Troubleshooting Steps

  1. If you smell gas, leave the home immediately and call your gas company or 911 from outside
  2. Turn off the gas supply to the furnace at the manual shut-off valve as a precaution

Call a professional when: Always call a professional for this code. A leaking gas valve is a serious safety hazard. Do not attempt to operate the furnace until it has been inspected by a licensed technician.

Trane 6 Flashes: 115V AC power reversed or poor grounding

High Urgency

The furnace has detected that the line voltage (115V AC) polarity is reversed (hot and neutral wires swapped) or the ground connection is faulty. The furnace will not operate safely with reversed polarity.

Estimated repair cost: $100 – $300

Common Causes

  • Hot and neutral wires reversed at the furnace connection
  • Faulty outlet or disconnect wired incorrectly
  • Poor or missing ground wire connection
  • Recent electrical work that affected the furnace circuit

DIY Troubleshooting Steps

  1. If recent electrical work was done, contact the electrician who performed the work
  2. Do not attempt to rewire the furnace — this is an electrical safety issue

Call a professional when: Always call a licensed electrician or HVAC technician. Reversed polarity is an electrical safety hazard that can damage the control board and must be corrected by a professional.

Trane 7 Flashes: Gas valve circuit error

High Urgency

The control board has detected a problem in the gas valve circuit. The valve may not be receiving the proper voltage signal, or there is a wiring issue between the control board and the gas valve.

Estimated repair cost: $200 – $650

Common Causes

  • Loose or damaged wiring between the control board and gas valve
  • Defective gas valve solenoid
  • Failed control board gas valve relay
  • Corroded wire connections at the gas valve

DIY Troubleshooting Steps

  1. Turn off the furnace power and visually inspect the wiring connections at the gas valve for loose or burned wires (do not touch while power is on)
  2. Try resetting the furnace by cycling power off for 30 seconds

Call a professional when: This code requires professional diagnosis. Gas valve circuits involve both electrical and gas components that must be tested and repaired by a licensed HVAC technician.

Trane 8 Flashes: Low flame sense signal

Medium Urgency

The flame sensor is detecting a flame, but the signal (measured in microamps) is below the minimum acceptable threshold. The flame is burning but not being detected reliably, which will eventually cause the furnace to shut down.

Estimated repair cost: $100 – $300

Common Causes

  • Dirty flame sensor coated with oxidation buildup (most common cause)
  • Corroded flame sensor rod needing replacement
  • Low gas pressure causing a weak, unstable flame
  • Improper burner flame pattern due to dirty burners

DIY Troubleshooting Steps

  1. Clean the flame sensor — turn off power, remove the single mounting screw, slide out the sensor, and gently scrub the metal rod with fine steel wool or emery cloth until shiny, then reinstall
  2. Check that the flame sensor rod is positioned correctly in the burner flame path

Call a professional when: Cleaning the flame sensor does not resolve the code. A technician can measure the actual microamp reading (should be above 1.5-2.0 uA) and check gas pressure to determine if the sensor, gas pressure, or burners need attention.

Trane 9 Flashes: Igniter circuit or grounding problem

High Urgency

The control board has detected an issue with the hot surface igniter circuit, or there is a voltage leak between the line neutral and the 24V common (grounding problem). This can prevent the igniter from heating properly.

Estimated repair cost: $150 – $400

Common Causes

  • Cracked or failed hot surface igniter
  • Grounding issue with the furnace (improper or missing ground wire)
  • Wiring fault in the igniter circuit
  • Control board igniter relay failure

DIY Troubleshooting Steps

  1. Visually inspect the hot surface igniter through the sight glass — if it glows orange/red when the furnace tries to start but gas does not ignite, the issue may be gas-related rather than igniter-related
  2. Check that the furnace is properly grounded — the ground wire should be securely connected

Call a professional when: This code requires professional diagnosis to distinguish between an igniter failure, grounding problem, or control board issue. A technician will measure igniter resistance and check for voltage leaks.

Trane LED Off (no light): No power to the furnace

Medium Urgency

The diagnostic LED is completely dark, indicating no electrical power is reaching the control board.

Estimated repair cost: $0 – $300

Common Causes

  • Tripped circuit breaker at the electrical panel
  • Furnace power switch turned off
  • Blown control board fuse
  • Disconnected wiring

DIY Troubleshooting Steps

  1. Check the circuit breaker for the furnace at your electrical panel and reset if tripped
  2. Locate the furnace power switch (standard light switch on or near the furnace) and confirm it is ON

Call a professional when: The breaker keeps tripping or the LED stays off after confirming power is on. This indicates an electrical fault within the furnace.

Need Trane Repair in Central Texas?

Texas Temp Masters provides expert HVAC repair for Trane , American Standard, and all major brands in Killeen, Waco, Temple, and surrounding areas. Call (817) 704-0706 for fast, reliable service, or contact us online.

Error code information cross-referenced from manufacturer documentation, HVAC/appliance professional resources, and verified repair databases. Codes can vary by specific model and control board revision. Always verify against your unit's diagnostic label or owner's manual. Repair costs are estimates based on national averages. Last updated February 2026.

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