Definition: A Trane Furnace Error 6 (six flashes) indicates a 115 VAC power polarity reversal. This diagnostic code signifies that the furnace control board has detected that the incoming “hot” (typically black) and “neutral” (typically white) wires are swapped, or there is a significant failure in the grounding circuit preventing proper flame rectification.
⚠️ Safety Precaution: High Voltage
For your safety and to avoid voiding the warranty, please check the official docs.
If you are seeing this code, you are likely dealing with a furnace that refuses to ignite, leaving your home increasingly cold. You might hear the inducer motor kick on briefly, followed by a sudden shutdown and the persistent rhythmic blinking of the red diagnostic LED. While an electrical fault sounds daunting, this is a highly fixable issue that usually involves correcting wiring orientation or tightening a loose ground. However, because this involves line-voltage electricity, strict adherence to safety protocols is mandatory.
Don’t worry; by following the systematic diagnostic steps outlined below, you can identify the source of the polarity reversal and restore your heating system to safe operation.
Quick Repair Specifications
- Difficulty: Intermediate (Requires basic knowledge of electrical circuits and multimeter usage).
- Estimated Time: 45 to 90 minutes for thorough diagnosis and correction.
- Tools Needed:
- Digital Multimeter (capable of measuring AC Voltage and Continuity).
- Phillips Head and 5/16″ Nut Driver.
- Non-contact Voltage Tester (for secondary safety verification).
- Wire Strippers/Crimpers (if re-terminating wires is required).
- Estimated Cost: $0 – $20 (for minor wiring supplies) or $150+ (if the control board requires replacement).
Symptoms
When a Trane furnace encounters an Error 6 Polarity issue, the system will exhibit specific behaviors designed to prevent unsafe operation. Recognizing these symptoms is the first step in confirming the fault code.
- Diagnostic LED Pattern: The red LED on the integrated furnace control board will flash six times, pause, and repeat. This is the primary indicator of reversed polarity.
- Ignition Failure: The furnace may initiate the draft inducer motor, but it will fail to energize the hot surface igniter or open the gas valve. The system enters a safety lockout to prevent potential electrical shock or component damage.
- Intermittent Operation: In cases of poor grounding, the furnace might run occasionally but shut off randomly as the flame sensor fails to “prove” the flame due to a lack of a clean electrical path to ground.
- No Heat: The most obvious symptom is a lack of warm air despite the thermostat calling for heat.
Technical Explanation of the Fault
The Trane control board is a sensitive electronic component that requires a specific electrical orientation to function. Here is why the “Error 6” occurs from a technical standpoint:
- Improper Installation or Recent Electrical Work: The most common cause is “human error” during recent repairs. If an outlet, light switch, or the furnace junction box was recently serviced, the hot and neutral wires may have been switched. In AC circuits, while devices often “work” with reversed polarity, modern furnace boards use the neutral and ground as a reference point for flame sensing.
- Loss of Ground Integrity: The furnace uses a process called flame rectification. It sends a small current through the flame to the ground. If the ground wire is corroded, loose, or disconnected, the board cannot complete this circuit and may misinterpret the lack of ground as a polarity reversal.
- Vibration-Induced Loosening: Furnaces are mechanical systems that vibrate. Over years of operation, wire nuts can loosen or spade connectors can slip. If the neutral wire becomes intermittent, the fluctuating voltage can trigger an Error 6.
- Control Board Logic Failure: While rare, internal components on the circuit board (such as resistors or capacitors in the sensing circuit) can fail due to age or voltage spikes. When these components fail, the board can no longer “see” the correct polarity even if the house wiring is perfect.
Comprehensive Repair Guide
WARNING: LETHAL VOLTAGE PRESENT. Before attempting any repairs, you must turn off the power at the circuit breaker. Failure to do so can result in severe electrical shock, permanent injury, or death. Do not touch any electrical components with the power on unless specifically performing a live voltage test with a rated multimeter.
- Safety Disconnection and Access:
Begin by locating the dedicated furnace breaker in your electrical panel and switching it to the “OFF” position. Use a non-contact voltage tester at the furnace to ensure no power is present. Use a Phillips head screwdriver or a 5/16″ nut driver to remove the upper and lower furnace access panels. Safety Note: Most furnaces have a door interlock switch that cuts power when the panel is removed; do not tape this switch down. - Inspect the Junction Box:
Locate the metal junction box where the house power enters the furnace cabinet. Open the box and inspect the wire nuts. Ensure the Black (Hot) wire from the house is connected to the Black furnace lead, and the White (Neutral) wire is connected to the White furnace lead. If they are swapped, this is the definitive cause of Error 6. Correct the connections and secure them with high-quality wire nuts. - Live Voltage Polarity Test:
If the wiring looks correct, you must perform a live test. Use extreme caution. Re-apply power and set your multimeter to AC Volts (200V+ range).- Measure between Hot (Black) and Neutral (White): Should be ~120V.
- Measure between Hot (Black) and Ground (Green/Bare): Should be ~120V.
- Measure between Neutral (White) and Ground (Green/Bare): Should be 0V to 1.5V.
If you measure 120V between Neutral and Ground, your polarity is reversed at the source (outlet or breaker panel).
- Verify Chassis Grounding:
Turn the power back off. Set your multimeter to Continuity (the beep setting). Touch one probe to the green ground screw on the control board and the other to the metal furnace chassis. Then touch the other to the copper gas line (if metallic) or the main ground wire. You must have a “closed” circuit (0 ohms). If there is high resistance, clean the oxidation off the ground screw and retighten. - Check Control Board Terminals:
Inspect the “L1” (Hot) and “L2” (Neutral) spade connectors directly on the furnace control board. Sometimes these wires are swapped at the factory or during a previous board replacement. Ensure the wire marked “Hot” or colored black goes to L1, and the white wire goes to L2. - Reset and Final Verification:
Once connections are verified and tightened, replace the service panels. Ensure the door switch is fully depressed. Restore power at the breaker. Observe the LED; it should transition from the Error 6 flash to a “Slow Green” or “Steady Red” (depending on the specific Trane model’s “standby” code). Trigger a call for heat at the thermostat to confirm the igniter glows and the burner fires.
How to Prevent Error 6 Flashes
Proactive maintenance is the only way to ensure that electrical faults do not leave you without heat during a blizzard. Follow these safety-officer-approved protocols:
- Install a Dedicated HVAC Surge Protector: Furnace control boards are sensitive to “dirty” power and voltage spikes. A surge protector designed for HVAC systems can prevent the internal logic failures that cause “ghost” polarity errors.
- Annual Tightening of Terminals: During your annual professional maintenance, request that the technician checks the torque on all high-voltage terminations. Expansion and contraction from heat cycles can loosen wire nuts over time.
- Maintain Grounding Paths: Ensure that the ground wire is never used as a “convenience” ground for other appliances. The furnace should be on a dedicated circuit to minimize electrical noise that can interfere with the board’s polarity sensing.
FAQ
Frequently Asked Questions
Q: Can I just swap the wires if the furnace worked before with this wiring?
A: No. If the furnace previously worked and suddenly shows Error 6, the wiring didn’t “change itself.” Swapping wires to “trick” the board is dangerous. The issue is likely a failed ground or a deteriorating control board. Correcting the root cause is the only safe solution.
Q: My multimeter shows 30V between Neutral and Ground. Is that an Error 6?
A: Yes. This is known as “stray voltage” or a “floating neutral.” The control board requires a clean 0V reference. This usually indicates a loose neutral wire in a junction box somewhere between the furnace and the main electrical panel.
Q: Is Error 6 a fire hazard?
A: Reversed polarity itself isn’t always an immediate fire hazard for the furnace, but it is a major safety hazard for technicians. It means that components that should be “neutral” (safe) are actually “hot” (electrified). This can lead to accidental electrocution during routine maintenance, which is why the board is programmed to lock out.