Boiler scale

Calcium carbonate deposits that build up inside the boiler, on the heating element, and along internal piping. Forms when hard water is heated and minerals precipitate out of solution.

Why it matters — Scale insulates heating elements (causing them to overheat and fail), restricts flow in narrow channels, and gums up solenoid valves. Severe scale eventually causes catastrophic failures — split boilers, blown elements, stuck valves.

Good to know

• Prevention via filtration is dramatically cheaper than cure. A BWT bestmax filter on a home machine means you'll likely never need to descale.
• If scale builds up, descaling is a chemical process that can damage seals. Have a qualified technician do it — DIY descaling is risky.