The water level regulator and limiter control the water feed to the boiler maintaining the correct levels, indicated by the water level lights (orange). Should the water supply fail, the boiler will shut down and lock off automatically.
All water supplies contain minerals, in various concentrations depending on the water supply. These coagulate at 60°C and form boiler slurry. If this is not cleaned out of the boiler, it will thicken and form hard boiler scale.
Water contains calcium, magnesium, iron, chloride, oxygen, carbonic acid etc in varying degrees, dependant on the water supply from one area to another, causing boiler scale and corrosion.