ERR 09 displayed; unit may not detect inlet water pressure correctly and may skip or abort regeneration.

Safety: Turn off water and relieve pressure before removing any pressure sensor or fittings.

• Locate sensor: Identify the pressure switch or transducer on the inlet side of the Pentair valve (if your model is equipped with one).
• Inspect port: Remove the sensor and check the pressure port for debris, iron, or scale. Clean gently with a small brush and rinse.
• Check wiring: Inspect the harness from the sensor to the control board. Repair any damaged wires and reseat connectors.
• Electrical test: Use a multimeter to verify the sensor output (voltage or resistance) changes with pressure (consult service data for expected values). A flat or open reading indicates a bad sensor.
• Replace sensor: Install a new Pentair inlet pressure sensor / switch if defective. Use thread sealant approved for potable water and do not overtighten.
• Board check: If a known-good sensor still triggers ERR 09, the control board input may be faulty and the Pentair electronic control board should be replaced.