I have a Bradford White hot water heater with a power vent. After using hot water the blower will turn on and stay on for the proper amount of time. After shutting off it will turn on and off for seconds at a time. This goes on for 5 - 10 minutes. Can anyone suggest what causes this and what is needed to repair the problem?

The draft motor on that unit is controlled by the small circuit board/circuit device located in the service area at the base of the heater I believe. If the unit has a heat sensor in or around the exhaust power vent that could also be the problem.