Goodman Furnace 5 Flash Error Code — What It Means
A Goodman furnace flashing 5 blinks on the LED status light means flame sensed without a heat call — the flame sensor is detecting (or simulating) a flame signal when the control board has not called for heat and the gas valve should be closed. This is a safety fault. If the furnace thinks it sees a flame when there shouldn’t be one, it could indicate a stuck-open gas valve, a leaking gas valve that allows gas to flow and ignite, or a faulty flame sensor generating a false signal. The control board locks out the system.
Common Causes
- Shorted or contaminated flame sensor circuit — The flame rod lead wire is shorted to ground or has moisture/contamination causing leakage current that mimics a flame signal.
- Stuck-open gas valve — A gas valve that doesn’t fully close when de-energized allows gas to continue flowing and burning after the heat call ends.
- Nuisance fault from a grounded flame rod — The flame rod is touching the burner box or a metal surface, creating a ground path that produces a false ionization signal.
- Faulty control board — The board’s flame sense input circuit has failed and is reading voltage when none is present.
Step-by-Step Fix {#fix}
- Check the flame sensor wiring — Power off the furnace. Inspect the wire from the control board to the flame sensor. Look for insulation that’s melted against the heat exchanger, frayed wire, or a connector that’s touching metal. Repair any grounded insulation.
- Inspect the flame rod position — Confirm the flame rod is properly mounted and not touching the burner box or any other metal component. The ceramic insulator must hold the rod electrically isolated.
- Clean and test the flame sensor — Clean the rod with fine emery cloth. Reconnect and test: power on the furnace with NO call for heat. If the 5-flash fault appears within 30 seconds without heat, the sensor circuit is still faulted.
- Check the gas valve — After a heat cycle completes and the burners shut off, use a combustion gas detector near the furnace to check for residual gas flow. Any gas detected after shutdown suggests a leaking gas valve.
- Reset the system — Cycle the breaker off/on. If 5 flashes appear before a heat call is even made, the problem is the sensor circuit or board. If they appear only after a heat cycle, the gas valve is suspect.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor | Amazon | Replace if rod is corroded or cleaning doesn’t resolve false signal |
| Flame sensor wire harness | Amazon | Replace if wire insulation has melted or shorted to ground |
| Gas valve | Amazon | Replace if valve leaks gas after de-energizing; requires licensed gas work |
| Control board | Amazon | Replace if all sensor and wiring checks pass but 5 flashes persist |
When to Call a Pro
A stuck-open gas valve is a gas leak and safety emergency. If you smell gas or detect it with a sensor after the furnace shuts off, turn off the gas supply at the meter, ventilate the space, and call a licensed HVAC technician or your gas utility immediately.