A coil assembly in a fuel injector includes a magnetic core and; a winding wound around the core, the winding being overmoulded and forming a cylindrical overmoulding. An axial blind hole extends towards the interior of the coil assembly from a first surface to a distal end, the blind hole being suitable for housing at least one spring for loading a magnetic armature. The coil assembly is provided with a degassing hole passing through the core and the overmoulding from the blind axial hole to an axial outer cylindrical surface, the degassing hole being provided in the magnetic core and having a restriction that is arranged in a first section that is proximal to the blind axial hole.