When boilers of water are used for a very long time, then white layers get deposited on inside of these boilers? How can these white layers be removed?

When boilers of water are used for a very long time, then white layers get deposited on inside of these boilers. This happens due to boiling of hard water in the boilers as hard water. The insoluble salt’s precipitates will settle down present in hard water due to which a white layer is deposited. Washing the boilers with dilute hydrochloric acid can remove these white layers.