How to know when to go to the doctors. for a ruptured boil?

Symptoms : If you have swelling, pain, fever, redness or, feel ill, go see a doctor. Same if your boil is taking too long to heal.

Fevers/more redness: Drainage of a boil (rupture) is the key to resolution. Keeping it clean and washing with soap & warm water is usually sufficient. Fever, increasing redness, or continued drainage and increasing pain are signs that the infection may have spread and should be further evaluated by a doctor.