Bryant 355MAV Error Code Rapid Flashing: Reversed Line Voltage Polarity
What Does Code Rapid Flashing Mean?
A rapidly flashing LED on the Bryant 355MAV indicates that the 115 VAC line voltage polarity is reversed. The furnace requires correct polarity to operate its flame sensing circuit safely — the flame sensor uses the grounded neutral wire as a reference, so reversed polarity prevents reliable flame detection.
This wiring problem most commonly occurs after the furnace has been installed, a control board has been replaced, or an electrician has worked on the home's circuits. The hot (live) wire and the neutral wire are connected to the wrong terminals at the furnace's electrical connection point. It can also happen if the outlet or junction box serving the furnace was wired incorrectly.
The furnace will not operate reliably with reversed polarity even if it occasionally attempts to start. The flame sensing circuit cannot properly distinguish between a real flame signal and background noise when polarity is reversed, creating a potential safety issue. An electrician or HVAC technician must swap the wires with the power completely off to correct this condition.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Hot and neutral wires reversed at furnace connection | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The LED is rapidly flashing — an electrician or HVAC technician must correct the reversed wiring polarity
- The furnace was recently installed or serviced and now shows this rapid flash pattern
✓ Verified against manufacturer service manual — March 2026