What is the purpose of a water softener in boilers?

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The main idea is that boilers require softened water to prevent scale on heat-transfer surfaces. A water softener targets hardness by removing calcium and magnesium ions, which are the minerals that form scale. It works through ion exchange, swapping those hardness-causing ions for sodium (or potassium) ions, so the water becomes soft. With less hardness, scale buildup is reduced, heat transfer stays efficient, and corrosion risks tied to scale are lower.

Removing dissolved oxygen isn’t the function of a water softener; oxygen is typically removed by deaerators or oxygen scavengers to protect boiler metal. Reducing conductivity by removing dissolved salts isn’t the primary goal either—softening changes the ion mix, and can even increase conductivity in some cases due to added sodium. Adding minerals to balance water chemistry is the opposite of softening.