The control valve tells the softener when to regenerate. Most units use one of two approaches: a timer that regenerates on a set schedule, or a meter that regenerates after a set volume of water has run through the unit. Some valves combine the two. Knowing which one you are being offered tells you what to check before you buy.
How each type decides
A timer valve regenerates at a chosen time of day, usually after a set number of days. It does not depend on how much water you used, so it can regenerate while the household is away.
A meter-initiated valve counts water through a flow meter and regenerates after a set amount. It responds to actual use, but it relies on the hardness and capacity settings being correct. If those settings are off, the unit can regenerate too early, too late, or on a schedule that does not match your use.
Trade-offs to weigh
Timer valves are simple to understand and easy to predict. Their weakness is regenerating on a fixed schedule whatever the demand. Meter valves respond to use, which can suit a household whose water use changes from week to week. Their weakness is dependence on accurate settings and a working meter. Sediment or debris can affect a meter, so ask how the meter is protected.
Questions to ask before you choose
Ask what happens when power is lost. Some valves keep their settings in memory, some need battery backup, and some reset to factory defaults. Ask whether you can view and change the regeneration settings without a technician. Ask whether the display shows days or volume remaining, and whether you can start a regeneration by hand. Ask how the valve is programmed for your water hardness and household size, and request that the seller show you the numbers entered.
Compare the paperwork too
Ask for the valve manual and check whether the valve warranty is separate from the tank warranty. Ask whether the valve can be replaced without replacing the tank. Clear answers show you what is most likely to fail and how that failure would be handled.
Use a criteria list, not a brand story
When comparing options, write down the questions above and note how well each seller answers them. The rating methodology explains how this site weighs criteria when it compares softeners, and you can apply the same approach at home by deciding how much each criterion matters for your household before you look at any sales pitch.