I also have the same issue with a code F5 on a reach. The model is a EASI and serial number is ET-B-94-00986. This unit is a 24 volt system.
It turns on, and goes through the testing cycle, then it codes F5. I notice both contactor tips are fairly burnt and they both pull in, but after 2 to 3 seconds of it pulling in, it codes out.

Anyone has any suggestions or what this code means.

Thanks.