American Standard Furnace Code E12
Hard lockout
The fuse on the integrated furnace control has opened, so 24 volt control power is lost.
Manual wording: “Open fuse”
Documented for: A951X condensing and A801X induced draft furnaces with the seven-segment IFC display
Likely causes, most common first
- Open fuse
- Short in the low-voltage thermostat or accessory wiring
- Short in a control circuit component
What you can safely check yourself
- Note whether the code appeared right after a thermostat was replaced or new low-voltage wiring was run, and mention that to the technician
When to call a technician
Call a technician. The fuse blew because something shorted; replacing it without finding the short will just blow it again.
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 and Dedicated Downflow Gas-Fired, Direct/Non-Direct Vent, Single Stage Condensing Furnaces with High Efficiency Motor (88-A951X001-1D-EN) (American Standard Heating and Air Conditioning, A951X040BU3SAB through A951X120DD5SAB single-stage 95% condensing furnaces (Silver 95 family)) · checked 2026-08-25
- Installer's Guide - Upflow/Downflow/Horizontal Left/Right Gas-Fired, Single Stage Induced Draft Furnaces with High Efficiency Motor (88-A801X003-1C-EN) (American Standard Heating and Air Conditioning, A801X026AM2SC through A801X120DM5SC single-stage 80% induced draft furnaces (Silver 80 family)) · checked 2026-08-25