You should never flush an old water heater because that can cause leaks. If you have a new water heater, it should be flushed once a year and anode rod checked every two years. The anode rod keeps the minerals from attacking the water heater tank, thus increasing the lifespan of your heater.
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.