Control displays “Err 03” and the softener is stuck in one regeneration position (e.g., brine draw or backwash).

Safety first: Unplug the unit and place the softener in bypass to avoid unexpected movement of the valve.

Check valve position sensing:

• Locate the position switch/encoder: On many AO Smith valves, a small microswitch or optical encoder is mounted near the main cam, with a harness leading to the control board.
• Inspect for misalignment: Verify that the cam tab or flag that actuates the switch/encoder is properly aligned and not broken. If the cam has shifted on its shaft, reposition or replace it.
• Check switch operation: Manually rotate the cam slightly (with power off) and listen/feel for the microswitch clicking. If there is no click or the switch feels loose, it may be defective.
• Inspect wiring: Confirm the harness from the switch/encoder to the board is intact, with no cuts or corrosion at the connector.
• Reset and test: Reconnect power, clear the error (if the model allows), and run a manual regeneration to see if the valve now indexes through all positions.

If the error remains: Replace the valve position switch/encoder. If a new sensor does not resolve the issue, the control board may not be reading the signal correctly and may need replacement.