American Standard Furnace: 6 Flashes
Code 6 Flashes: The 115 volt AC line and neutral are reversed at the furnace, the furnace is poorly grounded, or supply voltage is too low
WarningShown as: 6 flashes, pause, repeat
The 115 volt AC line and neutral are reversed at the furnace, the furnace is poorly grounded, or supply voltage is too low.
Manual wording: “6 Flashes --- 115 volt AC power reversed, poor grounding or system voltage too low”
Documented for: *UD1 / *DD1 and CUB1 / CDB1 fan-assisted gas furnaces with the LED-only integrated furnace control
Likely causes, most common first
- 115 volt AC power reversed
- Poor grounding
- System voltage too low
What you can safely check yourself
- Note whether the code appeared right after electrical work, a new outlet, or use of a generator
- Check whether lights elsewhere in the house are dimming, which suggests a low-voltage supply problem
When to call a technician
Call a technician or electrician. Correcting line polarity, grounding, or a low-voltage supply is electrical work at the furnace and the panel.
A American Standard furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installer's Guide - Upflow/Horizontal, Downflow/Horizontal Gas-Fired Furnaces, "Fan Assisted Combustion System" (18-CD19D7-17) (American Standard Heating and Air Conditioning, *UD1A/*UD1B/*UD1C/*UD1D upflow and *DD1B/*DD1C/*DD1D downflow 80% fan-assisted gas furnaces) · checked 2026-08-25
- Installation, Operation, and Maintenance Guide - Upflow Only and Downflow/Horizontal Gas-Fired Furnaces "Fan Assisted Combustion System" (Pub. No. 41-5010-20) (American Standard Heating and Air Conditioning, CUB1A/CUB1B/CUB1C/CUB1D upflow and CDB1A/CDB1B downflow 80% gas furnaces) · checked 2026-08-25