Water Softener Brine Tank Overflowing: Causes and What to Do

How the brine tank is supposed to work

A water softener has two tanks: the resin tank that softens the water, and the brine tank that holds salt. During regeneration, the control valve draws salty brine out of the brine tank, rinses it through the resin and sends it down the drain line. Then it refills the brine tank with a measured amount of water, which dissolves salt for the next cycle.

Some water in the brine tank is normal for many softeners — how much depends on the design. The problem is water rising well above its usual level, or spilling out of the tank, or out of an overflow fitting that is not connected to a drain.

Common causes

A blocked or kinked drain line. If the drain line is pinched, frozen, clogged or raised too high, brine cannot leave during regeneration. The tank does not empty, and the next refill adds more water on top.

A clogged injector or screen. The injector (sometimes called the venturi) creates the suction that pulls brine out of the tank. Sediment or salt residue can block it or its small screen, so brine is never drawn out.

A control valve that keeps refilling. If the valve sticks in its refill step, or the refill setting is wrong, it keeps sending water into the brine tank.

A stuck or missing safety float. Many brine tanks have a float in a tube inside the tank that shuts off water if the level gets too high. If it sticks or is missing, there is nothing to stop an overfill.

An interrupted cycle. A power outage or a reset during regeneration can leave the softener partway through a cycle with the tank fuller than normal. After power returns, check the clock and settings; if the next complete cycle does not bring the level back to normal, one of the causes above is likely.

What to do right now

Put the softener in bypass. Most softeners have a bypass valve on the plumbing at the back of the unit. In bypass, the house still has water, unsoftened, and no more water goes into the softener.

Unplug it — only if it is safe. Unplugging stops the control valve from starting another cycle, but only do it if the outlet, the cord and the floor around you are dry. If the outlet or cord is wet, or you would be standing in water, turn off that circuit at the breaker first. If water keeps coming in while the softener is in bypass, the bypass may not be fully closed; shut the supply valve to the softener.

Check the drain line. Follow the small drain hose from the control valve to where it empties. Look for kinks, crushed sections, a frozen section in a cold space, or an end that has been pushed down into standing water.

Clean up spilled brine. Salt water is hard on floors, drywall and metal, and wet floors are slippery, so dry the area.

Do not keep forcing manual regenerations to try to "pump it down" if the tank is not drawing; each attempt can add more water. Do not open the control valve or the resin tank unless you know that model.

Overflowing vs. other softener problems

An overflowing tank is different from a softener that is no longer making soft water. Hard water with a normal tank level often points to a salt bridge — a hard crust of salt that leaves a hollow space underneath — or simply an empty salt tank. A softener that leaks at the bypass valve or the fittings behind it is a plumbing leak rather than a brine problem.

When to call a plumber

If the drain line is clear and the tank still fills or overflows, the injector, control valve or float needs to be inspected. Sonlight services water softeners on an existing softener loop, including bypass valve problems, and can inspect the unit and explain the options with a written price before any work begins — see water treatment and softeners.

Related: water treatment and softeners, leak repair if water is coming from the plumbing rather than the tank, and the Tri-Cities hard water guide. Every Tri-Cities service area gets the same evaluation before any work.