Boiler to generate steam and/or to heat water, comprising a metal container (12) provided with at least a feed aperture (14) to introduce water inside it. The boiler comprises a heating element (18) associated to the container (12), and at least one detection device (20) to detect the physical quantities inside the container (12), positioned in correspondence with at least one detection zone (22) on an external surface (24) of the container (12).