Why Do Dishwashers Develop Scale?

Dishwashers gradually build scale on the cabinet and ware. As deposits grow, cleaning results decline. Why does scale form? See the causes below.

Why dishwashers develop scale

1. In China, municipal water hardness is often allowed up to 450, so tap water carries abundant calcium and magnesium. On heating they form calcium carbonate—the scale you see.

2. Food soil and greasy residues from ware also promote scale.

3. Sand already present in tap water can settle in the machine, though this contributes less scale.

Problems caused by scale

1. Weaker wash results

Heaters collect scale first. Calcium carbonate is a poor conductor, so water may not reach set temperature in time. Scale can also block spray-arm jets; if one jet plugs, the arm may stop spinning and detergent never reaches the ware.

2. Higher power use

Scale isolates the heater from water and sharply cuts heating efficiency, so energy use rises.

3. Equipment damage

Uneven contact—water on one area of the heater and scale on another—creates large temperature differences that can destroy the heating element.

4. Health concerns

Chemical analysis of scale has found metals such as cadmium, lead, iron, arsenic, and mercury. Descaling regularly is important for both the machine and health.

Hard water is the main driver of dishwasher scale. Because scale hurts performance and health, clean it on a schedule. For descaling methods, follow the CHINENG website.