The answer to 'when to replace water softener' is that water softeners typically need to be replaced every 10-15 years. Over time, the internal components of the softener can wear out, reducing its efficiency and effectiveness. Signs it's time to replace your water softener include decreased water pressure, increased salt usage, and water that still feels hard even after going through the softener.
Regular maintenance and servicing can help extend the life of your water softener, but eventually the entire unit will need to be replaced. It's a good idea to have a professional plumber inspect your softener every 2-3 years to assess its condition and recommend when replacement may be necessary.