LYNN-Two separate house fires in the city earlier this week were accidental in nature, a fire investigator said Wednesday.A vacant home at 101 Grant St. went up in flames at about 11:30 p.m. Sunday and was likely caused by an electrical problem, Lt. Dave Legere of the Lynn Fire Department said.Ownership of the home was taken over by MassRealty and was in the process of being sold when the fire broke out.Meanwhile, an occupied house at 18 Elvir St. caught fire at about 6:15 p.m. Monday on a second floor kitchen near the stove, Legere said.Investigators received conflicting versions of events surrounding the fire, he said.Legere said he’s still not sure if the fire was caused by an electrical problem or cooking, but nevertheless said it was an accident.