Display shows “Err 04” and the time or regeneration settings will not save or stay accurate.

Safety first: Disconnect power at the outlet or breaker before touching any wiring.

Basic checks:

• Verify power supply: Confirm the AO Smith power adapter/transformer is the correct model and output (typically 24 VAC). Use a multimeter to check output voltage.
• Inspect the control board: Remove the control panel cover and visually inspect the PCB for burn marks, swollen components, or corrosion.
• Check connectors: Reseat all low-voltage connectors to the board, including the transformer input, motor, turbine, and sensor harnesses.
• Factory reset: Follow the user manual procedure to perform a factory reset of the control (often involves holding specific buttons for several seconds). Reprogram hardness, time, and regeneration settings.

If the error recurs: The control board’s memory section is likely damaged. Replace the electronic control board with the correct AO Smith part number for your model. If you are not comfortable working with electrical components, contact a qualified technician.