American Standard Furnace 5 Flashes
Safety faultShown as: 5 flashes, pause, repeat
Flame is being detected when there should be no flame present.
Manual wording: “5 Flashes --- Flame sensed when no flame should be present”
Documented for: *UD1 / *DD1 and CUB1 / CDB1 fan-assisted gas furnaces with the LED-only integrated furnace control
Likely causes, most common first
- Flame sensed when no flame should be present
- Gas valve leaking through or slow to close
- Flame sensing circuit fault
What you can safely check yourself
- Turn the furnace switch off and leave it off
- If you smell gas, leave the house and call the gas utility from outside
When to call a technician
Call a technician. A flame signal with the gas valve off points at the gas valve or flame-proving circuit and is not a homeowner repair.
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