A softener looks like two tanks and a plastic head, and it is really six components each with a distinct job. Knowing which is which turns most faults into a short diagnosis, because the symptoms map onto the parts fairly cleanly and almost none of the common failures are the resin everybody blames first.
The two tanks
The resin or mineral tank is the tall fiberglass vessel where softening happens, holding a bed of ion exchange beads that swap sodium for calcium and magnesium. Inside it a riser tube runs down the center to a slotted distributor at the base, which collects softened water without letting beads escape. The brine tank sits beside it, holds the salt, and makes the concentrated solution that recharges the resin. A float and safety valve in the brine tank stops it overfilling and flooding the floor.
The control valve
The head on top of the resin tank is the brain and the most complex part. It directs flow through the bed in service, then runs the regeneration sequence: backwash to lift and rinse the bed, brine draw to strip the accumulated hardness, slow rinse, and fast rinse before returning to service. It is metered, timed or a combination, and its internal seals and pistons wear. Most puzzling softener behavior, including regenerating at the wrong time or not at all, is this component rather than the media.
Injector, brine line and drain line
The injector, or venturi, is a small nozzle in the control head that creates the suction drawing brine from the salt tank. It is the most common single failure on a softener because it blocks with salt residue and sediment, and a blocked injector means no brine is drawn, so the bed is never recharged while the cycle appears to run normally. The brine line carries the solution across, and the drain line carries backwash and rinse water away. Both must be free of kinks and correctly routed with an air gap at the drain.
Diagnosing by part
Hard water at the tap with normal salt use points at the injector or a salt bridge, not at the resin. Salt not being consumed at all points the same way. Water in the brine tank above normal points at the float, the injector or the drain line. Beads appearing in the plumbing means a broken riser or distributor, and that needs the tank opening. Continuous drain flow points at the control valve seals. Our softener cost guide covers which parts are worth replacing against a whole unit.
Questions people ask about water softener system parts
What is the most common softener failure?
A blocked injector. No brine is drawn, so the resin is never recharged, while the regeneration cycle appears to run entirely normally.
What does the control valve actually do?
Directs flow through the bed in service and runs regeneration: backwash, brine draw, slow rinse and fast rinse before returning to service.
There are beads in my plumbing, what broke?
The riser tube or the bottom distributor in the resin tank. That needs the tank opening, and new media alone will not fix it.
The salt is not going down, is the softener broken?
Usually a salt bridge or a blocked injector rather than the resin. Check for a crust across the brine tank before anything else.