Water remains hard even though the AO Smith water softener appears to run and regenerate normally.

Safety first: No electrical work is required for basic checks, but unplug the unit if you will open the control head.

Verify basic settings and plumbing:

• Check that the bypass valve is fully in Service position.
• Confirm the hardness setting on the control matches your actual water hardness (use a test kit or lab report).
• Ensure the salt dosage or capacity setting is appropriate for your usage and hardness.

Check regeneration function:

• Initiate a manual regeneration and verify that each stage (backwash, brine draw, rinse, refill) occurs and that brine is actually drawn from the tank.
• After regeneration, test water hardness at a softener-fed faucet.

Resin condition:

• If the unit is several years old and performance has gradually declined, the resin may be iron-fouled or exhausted.
• Consider cleaning with a resin cleaner approved for AO Smith systems (follow product directions), or replace the resin media if cleaning does not restore performance.