Hunter EC Controller Displays "NO" and Won't Run Programs

Diagnosing a Hunter EC Controller Stuck on "NO"

A Hunter EC series controller shows "NO" on the display and refuses to run programs or manual cycles. The user has already unplugged the unit, replaced the backup battery and fuse, but the message persists.

Two Likely Culprits

1. Transformer failure: The controller may not be receiving the correct 24 VAC output. Use a volt/ohm meter to verify input and output voltage.
2. Frozen display: The controller's microprocessor may be locked up. A full reset often resolves this.

Reset Procedure (from Owner's Manual, Page 10)

Refer to the Hunter EC owner's manual for the exact reset steps. Generally, you disconnect power, remove the battery, wait a few minutes, restore power, and press the reset button.

If the transformer checks out and a reset doesn't help, the controller itself may need replacement.