A water softener in bypass sends untreated water through the house. Nothing fails loudly. The control head may still show a time, the brine tank may look normal, and the unit may still have power. The first sign is usually a change at the tap, so start your check at the valve, not the control panel.
Where the bypass gets left
Bypass is often set during installation, when a technician isolates the unit to test lines, and again during repairs, filter changes, or any job that required shutting off water to the softener. The valve is then turned back by hand, sometimes by someone who was only tidying up and did not know which position was correct. Some systems use a bypass handle or lever on the valve assembly. Others use a set of ball valves on the inlet and outlet piping. Whichever type you have, look at the actual position before assuming anything.
Check the tap before you open the cabinet
Run the cold tap and then the hot tap for about a minute each. Compare what you see with what you normally see. Hard water typically shows up as soap that lathers poorly, a film on dishes and glassware, spotting on faucets, and a stiff feel to laundry. Hot water may show the problem first, because hardness builds up in the water heater. If the change began on a particular day, think back to whether anyone worked on the softener, the plumbing, or the water heater around then.
Check the valve position
Work through these steps in order:
1. Find the installer's label or the manual, which should identify the service position for your valve.
2. Compare the handles, lever, or ball valves with that description. Water should pass through the softener in service. In bypass, the setting diverts water around it.
3. Do not force a stuck handle. If it resists, stop and call for service rather than working it back and forth.
4. Look at the control head. It should show a current time and an operating status. A blank or wrong display points to a power or programming problem, which is a separate check.
5. After you return the valve to service, run a tap for a few minutes and compare it with the earlier test.
What to ask the installer or service provider
Ask which valve position is normal for your system and whether it is labeled on the unit. Ask whether the last visit left the bypass in place, and whether they will mark the valve so the next person can see the correct setting. If you are comparing providers, ask how they handle the valve after maintenance and whether that step appears on the service record. The Missouri Water Softener Buyer's Guide covers what to ask about installation and service in more detail.
When the valve is correct but hardness returns
If the valve is in service and hard water still reaches the tap, the cause is somewhere else. Check the salt level, look for salt bridging, and confirm that the regeneration schedule matches your household's water use. Those checks are separate from the bypass question, so do not assume the valve is the whole answer. If you cannot find a clear cause after these checks, call for service and describe what you saw at each tap and what the valve position was when you checked it.