When hard water, sediment, or an off taste comes back after a filter or softener was serviced, the equipment is often blamed first. Before you accept that, check the bypass valve. A bypass left in the wrong position sends water around the treatment equipment, so every tap in the house gets untreated supply while the unit looks normal.
How a bypass assembly works
Most whole-house systems sit on a bypass assembly, a short run of pipe with valves that route water either through the equipment or around it. In normal service, the valves send water through the equipment and the bypass path is closed. When the valves are turned the other way, the water skips the equipment entirely.
Bypass positions are sometimes turned during service, for example to isolate the unit while a cartridge or media is changed, to flush the lines, or to test pressure. The step that fails is the return to service. If the handles are not set back, the unit sits idle while the house draws straight from the supply.
What the symptoms look like
Hard water returns at the taps, or the soft feel you had before disappears. A filter that was clearing sediment stops doing so, and grit or cloudiness reappears. Taste or odor changes that the filter was handling come back. The equipment itself may look fine, with no leaks, no alarms, and normal pressure at the tap.
A pressure drop is a different issue, caused by a restriction. If your pressure is low, the bypass check below is still worth doing, but the cause may be elsewhere.
Check the valve before you call for service
Find the bypass assembly, usually on the supply line near the equipment. Before you touch any handle, take a photo of the current position so you can return to it if you need to.
Your equipment manual, or a label on the assembly, shows which handle positions mean in service and which mean bypass. Match the handles to that label, not to what you remember from the last visit. Many assemblies have arrows or words stamped on them.
Confirm that every valve handle is in the in-service position described on the label. If one handle is turned and the other is not, the unit may be partly bypassed and still send some untreated water to the house.
Run a few taps for a few minutes after resetting, then compare the water to what you had before the service. If the difference returns at the taps, the bypass was the cause. If it does not, the problem lies with the equipment or the water source, and the service provider should be asked to explain what they found.
Ask the service provider to confirm it in writing
At the end of every service visit, ask the provider to show you the bypass position and confirm it in the service record. A simple note stating that the equipment is in service and the bypass is closed protects you the next time a problem appears. If the record says the unit was bypassed for testing, ask when and by whom it was returned to service.