Investigators believe that a faulty gas appliance may be linked to the deaths of Aaron Davidson and Neil McFerran in Castlerock, Co Derry, on Tuesday night.
Investigators have discovered a faulty gas appliance in the apartment. They cannot yet say definitively if this caused the deaths.
The parents of Neil McFerran and Aaron Davidson became concerned when their sons were not answering their mobile phones on Tuesday.
They drove almost 112km from Newtownabbey to Castlerock, where the 18-year-old boys were spending a few days with a friend in a relative's holiday apartment.
A third young man who was successfully resuscitated continues to make progress in hospital.