Controller display shows “Err 0” and the valve will not start a regeneration cycle automatically.

Safety first: Unplug the softener’s power supply before opening the control housing. Water is present nearby; keep hands dry and avoid working on live circuits.

• Power cycle the control: Unplug the Fleck power adapter for 2–3 minutes, then plug it back in. Check if the display returns to normal and if the time-of-day can be set.
• Verify correct transformer: Confirm the wall transformer matches the valve (typically 24 VAC output, correct amperage). Using the wrong transformer can corrupt or lock the control.
• Reset to factory defaults: Enter the master programming mode (refer to the specific Fleck model manual, e.g., 5600SXT, 5810SXT, 7000SXT, XTR2). Perform a factory reset, then re-enter hardness, capacity, and regeneration settings.
• Inspect control board: Remove the front cover, check for burn marks, swollen components, or corrosion on the SXT/XTR board. Reseat the ribbon cable and connectors.
• If Err 0 persists: The control board memory is likely damaged. Replace the complete control board module with the correct Fleck OEM board for your valve model.