Goodman GMEC960803BN Error Code Red 9 Flashes: Grounding or Reversed Polarity

What Does Code Red 9 Flashes Mean?

Nine red flashes on the Goodman GMEC960803BN's Integrated Control Module indicate improper grounding or reversed polarity in the 115-volt supply. The board relies on a correct hot/neutral/ground reference for its flame-sensing and safety logic, so it actively checks polarity and refuses to operate if it is wrong.

When this code appears, the hot and neutral wires feeding the furnace are typically reversed, or the ground connection is missing or poor. On a correctly wired furnace the hot leg (through the door switch to the board's L1) reads 115 volts to ground and to neutral, while neutral reads about 0 volts to ground. A reversed connection, or a bad ground, disrupts the reference the board uses to sense flame reliably.

Because the flame-sensing circuit depends on proper polarity and grounding, the board treats this as a high-severity electrical fault. It often shows up right after new wiring, a receptacle change, or work at the panel, and correcting it involves line-voltage wiring that must be handled by a qualified electrician or technician.

What You'll Notice

• The furnace will not run and the board flashes red nine times
• The problem appeared right after electrical work, a new outlet, or a furnace relocation
• The furnace may have never worked correctly since installation if wired wrong from the start
• No heating operation despite a valid thermostat call
• The fault is present consistently rather than intermittently

Common Causes

How This Is Diagnosed

Because the board flags a polarity or grounding problem, a technician verifies the incoming line wiring with power present: the hot leg should read 115 volts to both ground and neutral, and neutral should read near 0 volts to ground. They confirm the ground connection is solid and that hot and neutral are not swapped at the furnace, the receptacle, or upstream. This is line-voltage electrical work and must be done by a qualified professional.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The code appeared after electrical work, a new receptacle, or moving the furnace
• You are not qualified to verify line-voltage polarity and grounding
• The furnace has never run correctly since installation
• Any correction of hot/neutral/ground wiring, which is professional electrical work

✓ Verified against manufacturer service manual — March 2026