Truth be told, there is only going to be one reason your vest does not receive heat. It is all going to come down to the electrical components and this includes the battery. First off, ensure that the battery pack is correctly connected to the plug. As simple as it sounds, this can be the issue. Next up, actually ensure that the battery is charged. If you know for a fact that both of these are not the issue then there may be some internal damage. You may want to contact the manufacturer if this is the case.