We consider self-magnetization of charged and neutral vector bosons bearing a magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a divergence of the magnetization in both the medium and the electroweak vacuum occurs for the critical field . For B > B_wc the system is unstable. This behavior suggests the occurrence of a phase transition at B = B_c, where the field is self-consistently maintained. This mechanism actually prevents B from reaching the critical value B_c. For virtual neutral vector bosons bearing an anomalous magnetic moment, the ground state behavior for have a similar behavior. The magnetization in the medium is associated to a Bose–Einstein condensate and we conjecture a similar condensate occurs also in the case of vacuum. The model is applied to virtual electron-positron pairs bosonization in a magnetic field , where m_e is the electron mass. This would lead also to vacuum self-magnetization in QED, where in both cases the symmetry breaking is due to a condensate of quasi-massless particles.