Igniter
Price the ignition part only after confirming the model number and connector.
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
- 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 | Replace if rod is corroded or cleaning doesn’t resolve false signal |
| Flame sensor wire harness | Replace if wire insulation has melted or shorted to ground |
| Gas valve | Replace if valve leaks gas after de-energizing; requires licensed gas work |
| Control board | Replace if all sensor and wiring checks pass but 5 flashes persist |
Technician Tips
Goodman furnaces use a simple LED flash system on the control board. The diagnostic LED is usually visible through the blower compartment window. Count the flashes between pauses — that’s your error code. One flash = normal operation. Two flashes = pressure switch fault. Three flashes = limit switch. Four flashes = flame sensor. Goodman flame sensors are notorious for carbon buildup — cleaning with emery cloth every 2-3 years prevents most lockout calls. The control board on GMS8 and GMSS9 models is particularly sensitive to voltage fluctuations — if you see multiple different codes, check the transformer output (should be 24VAC ±10%).
Prevention: Install a whole-house surge protector on the furnace circuit to prevent board damage from power spikes.
Need Replacement Parts?
Before ordering, match the furnace part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
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.