American Standard Furnace Flashing Slow
StatusShown as: Red LED flashing slowly and steadily
Normal standby. The control board is powered and healthy and the thermostat is not calling for heat.
Manual wording: “Flashing Slow --- Normal - No call for Heat”
Documented for: *UD1 / *DD1 and CUB1 / CDB1 fan-assisted gas furnaces with the LED-only integrated furnace control
Likely causes, most common first
- Normal operation with no heat call from the thermostat
What you can safely check yourself
- Check the thermostat - make sure it is set to Heat and set higher than room temperature
- Check thermostat batteries if it has them
When to call a technician
No service needed. If the thermostat is calling for heat and the LED stays on the slow flash, the heat call is not reaching the furnace and a technician should check the thermostat and its wiring.
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
- Furnace Troubleshooting - American Standard owner support (American Standard Heating and Air Conditioning, American Standard residential gas furnaces (general)) · checked 2026-08-25