The digital controls are designed to notify you in the event that a problem has been discovered. By flashing "FF" on the display the control is indicating a problem with the heater.
First check the blanket/mattress pad for visual damage. If no visual damage is found, unplug the system from wall outlet. Check that the control is well-connected to the module. Plug the power cord into the wall outlet. Set the control to "On." If the system still does not operate after 2 or 3 times trying to reset, disconnect the power cord and contact service.
The following link contains the owner's manual for the blanket and it may be useful to you in resolving this problem.
I hope this information is helpful to you but submit another question with any additional details for further assistance.