When hiring a plumber, make sure you ask to see a Plumber’s License. A Plumber’s License is a certification that the technician has passed a written exam, has undergone the required hours of supervised training and has completed continuing education classes every 2 years. Having a licensed plumber ensures that you will have someone knowledgeable about plumbing and local plumbing codes. Just because a technician works for a plumbing company with a business license does not mean that technician is a certified plumber.