Start by looking at the board, not the blink. If your furnace shows its codes on a red LED that sits next to separate green and amber LEDs — the GMEC96/GCEC96 generation — one red flash means the control is sensing flame when no flame should be there. That is a short list of bad actors: a gas valve stuck or leaking open, valve wiring faults, or a shorted flame rod, per Goodman's own chart.
If your furnace has a single diagnostic LED — the older control — scroll down: your 1 flash means something completely different, and much less alarming.
1 red flash: Flame sensed when no flame should be present
Safety stop — furnace off, call a technician
The manual points at a gas valve stuck open, wiring faults at the valve, or a shorted flame rod. This is a gas code, not a reset code.
From the table: Red-LED chart — two-stage 96% furnaces — source: Goodman GCEC960803BN Installation Instructions, Troubleshooting Chart, pp. 55-56 (read the document, fetched 2026-10-30). Covers: GMEC96 / GCEC96 and their Amana twins — the current two-stage condensing furnaces with a green/amber/red LED trio on the board.
On the older single-LED board: 1 flash = external lockout
Goodman's PG-series instructions give 1 flash as external lockout: the furnace could not establish measurable combustion in three consecutive ignition attempts — flame not proven inside the 7-second trial, a 30-second purge, retry, three rounds, then lockout. It auto-resets after an hour. The manual's own check list for the technician is gas pressures, orifices, the gas valve, and the flame sensor. For the older board, the answer box above does not apply — use the basics list instead: thermostat calling, gas valve at the furnace open, filter clean, one reset, then call if it repeats.
Older-board source: Goodman PG15 Installation Instructions, "Abnormal Operation - Heating" (read it).
Safety stop — furnace off, call a technician — the safe list:
- Turn the furnace off at its power switch and leave it off.
- This code means the control thinks flame or gas is present when it should not be, or that a flame-safety switch has opened. Resetting it is not a fix.
- Call a licensed HVAC technician. If you smell gas at any point: leave the house and call your gas utility or 911 from outside.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
Questions
Which Goodman board do I have?
Three LEDs (green, amber, red) on a 96% two-stage furnace: the GMEC96 chart, and 1 red flash is the flame-sensed code. A single diagnostic LED: the older chart, and 1 flash is ignition lockout. The model number’s first letters settle it — GMEC/GCEC versus the older single-stage families.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.