The serial that is displayed for a generator in FLEET is the serial number that we are able to read from the generator's controller. This means we are pulling the serial number that is encoded on the controller. All "F's" means that there is no serial number encoded to that specific controller.
This is most common when the control panel is replaced. Replacement controllers obtained through warranty replacement or service parts, do not have serial numbers encoded on them and at this time there is no option on the controller to enter an updated serial number.
NOTE: In rare cases, problems are identified during end of production, as a result the controller is replaced. At that point, they immediately re-encode the serial number on that new controller, however, there may be rare cases where this step is missed. In this case, a new generator may ship without a serial number encoded on the controller, resulting in all "F's" being read.
We are working to add a feature to FLEET to allow the user entered serial number to be displayed when all "F's" is being read from the controller.