Viral gastroenteritis: This is a common cause of fever in infants, especially in the absence of other symptoms like URI or UTI. The virus can cause inflammation in the stomach and intestines, leading to fever, vomiting, and diarrhea.

Roseola: A viral illness that typically affects children under the age of 2, characterized by a high fever followed by a rash. The fever can be present without any other symptoms initially.
Infectious diarrhea (bacterial): Bacterial infections like Salmonella or Shigella can cause fever, diarrhea, and abdominal pain in infants.
Otitis media: Although the question rules out URI, it's possible for an ear infection to present with fever as the only symptom, especially if the child is too young to complain of ear pain.

Meningitis: A potentially life-threatening infection of the meninges that requires prompt diagnosis and treatment. Fever, irritability, and lethargy can be early signs, even in the absence of other symptoms.
Bacteremia or sepsis: Bacterial infections in the blood can cause fever, and it's crucial to identify and treat them promptly to prevent serious complications.
Pneumonia: Although the question rules out URI, pneumonia can sometimes present with fever as the only symptom, especially in young children who may not produce typical respiratory symptoms.

Kawasaki disease: An autoimmune condition that can cause fever, rash, and other symptoms. It's rare but important to consider, especially if the child has a prolonged fever without an obvious source.
Juvenile idiopathic arthritis: A chronic condition that can cause fever, joint pain, and swelling. It's rare in infants, but can be considered if other causes of fever are ruled out.
Neonatal herpes simplex virus (if the child is still under 3 months) or other congenital infections: Although less likely at 14 months, if the child was premature or had other risk factors, these infections could still be considered.