Goodman 5 Flash Error Code — What It Means
Five flashes on a Goodman furnace diagnostic LED indicates “Flame Sensed When No Flame Should Be Present” — the flame sensor is detecting a signal during a period when the gas valve is closed and no burner should be lit. This is a safety lockout. The control board interprets a voltage signal from the flame sensor without a corresponding call for heat as a dangerous condition (potential gas leak igniting outside the normal sequence) and shuts the furnace down.
Common Causes
- Leaking or sticking gas valve — A gas valve that does not fully close allows a small amount of gas to reach the burners, which can ignite from residual heat and produce a flame signal.
- Contaminated or shorted flame sensor — A sensor rod coated with oxidation or silicate deposits may produce a false microamp reading even without flame present.
- Wiring short to the flame sensor circuit — A pinched or chafed wire between the sensor and the control board can induce voltage on the sensor circuit, mimicking a flame signal.
- Faulty control board — Rarely, the board’s flame-sensing circuit malfunctions and reports flame when none exists.
Step-by-Step Fix {#fix}
- Turn off gas supply — Shut the manual gas shutoff valve upstream of the furnace before any inspection. Confirm no gas odor is present before proceeding.
- Inspect and clean the flame sensor — Remove the flame sensor rod (one screw, quarter-inch connector). Clean the rod with fine steel wool or 400-grit emery cloth. Reinsert and tighten.
- Check flame sensor wiring — Trace the wire from the flame sensor to the control board. Look for any areas where insulation is worn, pinched by a panel edge, or melted. Repair or replace the wire as needed.
- Test the gas valve — With gas on and the furnace in standby (not calling for heat), use a combustible gas detector near the burner compartment. Any gas reading indicates a leaking valve that must be replaced.
- Reset and test — Restore power, restore gas, and run a full heat cycle. If the 5-flash code returns immediately after burner shutoff (no call for heat), and the flame sensor and wiring are clean, replace the gas valve or control board.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor rod | Amazon | Inexpensive universal or OEM; clean before replacing |
| Gas valve | Amazon | Replace if leaking through in standby; match BTU rating |
| Flame sensor wire lead | Amazon | Replace if insulation is damaged |
| Control board | Amazon | Last resort after other components verified |
When to Call a Pro
Any suspected gas valve leak requires a licensed gas technician. Do not operate the furnace if you smell gas or a combustible gas detector reads positive near the burner — evacuate and call your gas utility.
See Also
- Goodman Furnace E1 Error Code — Causes & Fix
- Goodman 7 Flash Error Code — Ignition Lockout Fix
- Goodman 3 Flash Error Code — Pressure Switch Stuck Open Fix
- Goodman 9 Flash Error Code — Causes & Fix