Goodman furnace 9 red flashes: Grounding problem or reversed polarity
Nine red flashes means the furnace has an electrical supply problem — either line and neutral are reversed, or the grounding is inadequate. It is a wiring fault rather than a broken component.
Applies to: Goodman GMEC96 and Amana AMEC96 two-stage gas furnaces with a three-colour diagnostic LED.
What it means
Flame detection works by rectification, passing a very small current through the flame to ground. That requires both correct supply polarity and a solid ground path, so the control checks for them before it will operate. This code means the check failed. It is worth recognising as a wiring fault rather than a component failure, because it almost always follows electrical work or a new installation. A furnace that ran for years and suddenly shows this usually means something in its supply circuit has been changed or has come loose.
Most common causes
- Line and neutral reversed at the furnace, at a junction box, or at the outlet feeding it.
- A missing or disconnected ground wire at the furnace chassis.
- A loose blower motor ground or low voltage common ground.
- A loose neutral connection in the circuit.
- A recently replaced outlet or newly run circuit wired incorrectly.
- A furnace that has been moved, replaced, or reconnected.
- A control board that has failed in a way that misreads the supply.
How to diagnose it
- Establish whether any electrical work has been done recently, in the house generally rather than only at the furnace.
- If the furnace is newly installed or reconnected, treat this as an installation fault.
- Note whether other faults have appeared alongside it. Grounding and polarity problems also produce weak flame signal and igniter codes, so a cluster usually has one cause.
- Do not test the supply yourself unless qualified to work at a live panel.
How to fix it
- This is electrical work on the furnace supply and belongs to a licensed electrician or heating technician.
- If the furnace was just installed or reconnected, call whoever did the work — this is a wiring error, not a developed fault.
- Have the ground path checked as well as the polarity, since this code covers both.
- Do not attempt to bypass the check. The control is refusing to run because it cannot trust its own flame detection.
Notes
Because the same conditions break flame sensing, a furnace showing this alongside a history of intermittent ignition faults usually has one electrical cause behind all of them. Fixing the supply often clears several codes at once.