A softener that is working properly is quiet and predictable. When it starts running at odd hours, draining longer than it should, or using salt faster than usual, the control valve or its timer is often the first place to look. An early catch is far easier than a service call after the water schedule has already gone wrong.
Signs worth noting in the first weeks
Watch for regeneration at a time you did not set, such as in the middle of the night when the house is quiet. Note a long drain noise, a steady trickle at the drain line when no one is using water, or a display clock that has drifted from the real time. A salt level dropping faster than the company's estimate is another signal, although salt use also depends on how many people are home and how much they use.
Check what you can see without opening anything
Once a week, look at the drain line and listen near the unit for steady flow. At night, when no faucet is running, check the water meter if you have one and see whether the reading moves. Jot down what you see each time, along with the time of day and what was running. These notes give the technician facts to work from. Do not open the control valve, take the unit apart, or try to reset the timer on your own, because a wrong setting can cause the same problem again.
What to ask the company
Ask whether the program is set by time, by water used, or both, and what your current settings are. Ask who will diagnose the valve, whether they will check the timer against the actual water use in your home, and whether the visit is a diagnosis only or includes a repair. Ask also how to shut off water to the unit if the valve starts leaking, so you know the steps before you need them.