Display shows ERR4 and valve stops in an unknown position during regeneration

Safety: Disconnect power and shut off water. Depressurize the system before opening the valve head.

• Inspect cam and gears: Remove the control cover and visually inspect the main cam and drive gears. Look for signs that the cam has slipped on its shaft or that a gear is partially stripped.
• Verify piston orientation: Remove the piston assembly and confirm it is installed in the correct orientation for a softener (not a filter) and matches the US Water Systems valve model. Incorrect pistons or misaligned spacers can cause the valve to stop in invalid positions.
• Re-time the cam: Many valves have timing marks on the cam and housing. Align the cam to the "Service" mark and reinstall the drive gear according to the service manual so that the motor starts from the correct reference position.
• Check programming: Enter the installer menu and verify that the valve type, number of cycles, and cycle times match the physical valve (e.g., 5-cycle softener, upflow/downflow brining). Incorrect configuration can cause the board to drive the valve beyond its mechanical range.
• Test operation: Restore power and initiate a manual regeneration. Observe the cam as it moves through each cycle. If it still overshoots or stalls, the control board may be defective and require replacement.