from what i read here - i am assuming you have baseboard heat. many times a contractor will not add bleeder vales on baseboard radiators. the bleeding of air is done primarirly during the onset of cooler weather. this is done by a purge vavle. it will look a little different than a normal valve in the aspect that it will also have a hose connection on it. you open the auto feed valve fully and then run water through system and out the hose. it may have a cock on it to isolate the boiler from the hose conncetion. if not there may be an extra valve installed to do this.