American Standard S8X1 furnace code COf: Continuous fan
Info — not a fault
What does COf mean on an American Standard Silver S8X1 gas furnace display? COf means the thermostat is calling for continuous fan. The blower runs without a heating or cooling call, so register air stays near room temperature.
Safe checks before calling
To stop constant room-temperature airflow, set the thermostat fan from ON to AUTO.
Questions about this code
What does COf mean on an American Standard Silver S8X1 gas furnace display?
COf means the thermostat is calling for continuous fan. The blower runs without a heating or cooling call, so register air stays near room temperature.
Does American Standard S8X1 furnace code COf mean I need a repair?
COf needs no repair. Book service only if COf appears while the thermostat fan is set to AUTO and no schedule is calling for fan.
How much does it cost to fix American Standard S8X1 furnace code COf?
Continuous fan is a normal state and implies no repair bill on its own. A visit is only needed if the fan runs without a thermostat request.
Applies to
S8X1A040M3PSCA · S8X1B040M2PSCA · S8X1B060M4PSCB · S8X1B080M4PSCB · S8X1C080M5PSCA · S8X1C100M5PSCB · S8X1D120M5PSCA
Different American Standard generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Verified against Installation, Operation, and Maintenance — Upflow/Downflow/Horizontal Gas-Fired,1–Stage and2–Stage Induced Draft Furnaces with High Efficiency Motor, p.55
Last verified 2026-10-07 · page updated 2026-10-07 · how we verify
Related American Standard furnace codes
These codes use the same american standard silver s8x1 furnace control display (2024 iom) system.