Goodman GMSS920803BN Error Code Continuous/Rapid Flash: Reversed Polarity
What Does Code Continuous/Rapid Flash Mean?
A continuous, rapid flash on the Goodman GMSS920803BN diagnostic LED indicates reversed electrical polarity. The Integrated Control Module has detected that the incoming 115-volt or 24-volt supply is wired with hot and neutral swapped, and it blocks operation until the wiring is corrected. The board needs correct polarity to reference ground properly for its flame-sensing and safety functions, so it treats reversed polarity as a stop condition.
The most common cause is the 115-volt hot and neutral conductors being reversed at the furnace connection — something that happens during installation, after panel or circuit work, or when the furnace is fed from a receptacle that is itself miswired. On this model the transformer's orange and gray leads being reversed can produce the same code, and a poor or missing unit ground can interfere with polarity detection and trigger the flash even when hot and neutral are correct.
This pattern is easy to distinguish from the board's other power-related indications. A completely dark LED means the module has no power at all, while this continuous rapid flash means the board is powered and actively reporting that the power it is receiving is wired backward. That difference tells a technician to check wiring polarity rather than hunt for a lost power source.
What You'll Notice
- The diagnostic LED flashes rapidly and continuously rather than in a counted pattern
- The furnace will not start any part of the heat sequence — no inducer, no igniter, no blower
- The problem appears right after installation, an electrical repair, or a move to a different circuit or outlet
- Other outlets on the same circuit may test as reverse-wired
- The furnace never worked correctly from the moment of a recent wiring change
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| 115V AC power wires reversed | Most common | ✗ Call a pro → |
| Transformer wires (orange and gray) reversed | Common | ✗ Call a pro → |
| Poor or missing unit ground | Common | ✗ Call a pro → |
How This Is Diagnosed
Because the board is reporting the power it receives is backward, diagnosis centers on wiring polarity. With appropriate precautions, a technician verifies the 115-volt hot and neutral at the furnace connection against the wiring diagram, confirming line and neutral are landed on the correct terminals rather than swapped.
If line-side polarity is correct, they check the transformer's orange and gray leads for a reversal and verify the unit ground, since a poor ground can cause the board to misread polarity. The fix is a wiring correction — reversing swapped conductors or restoring the ground — which is electrical work for a qualified electrician or HVAC technician, not a homeowner repair.
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 LED flashes continuously and the furnace will not operate
- The furnace was recently installed or had electrical work done just before the code appeared
- A receptacle tester shows reversed polarity at the furnace circuit or nearby outlets
- The wiring at the furnace looks incorrect or was recently changed
- You are not qualified to verify and correct 115-volt wiring polarity safely
Frequently Asked Questions
Why won't my Goodman GMSS920803BN run when the LED flashes continuously?
The board has detected reversed line polarity — hot and neutral are swapped somewhere in its supply. It needs correct polarity to reference ground for its safety and flame-sensing functions, so it blocks operation until the wiring is corrected.
The furnace worked before — why reversed polarity now?
Reversed polarity almost always follows a wiring change: a new installation, panel or circuit work, or moving the furnace to a different outlet. Something in that change swapped hot and neutral, or the transformer leads or ground were disturbed.
Can I fix reversed polarity myself?
No. Correcting it means working on 115-volt wiring to identify and reverse the swapped conductors or restore the ground, which is a job for a licensed electrician or HVAC technician for both safety and code reasons.
Sources
✓ Verified against manufacturer service manual — March 2026