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.
Related
All codes for this manufacturer
Goodman and Amana furnace fault codes — every code, with what differs between models.