F71USER INTERFACE HEARTBEAT FAILURE
If a Central Control Unit Heartbeat Failure is displayed, no communication is detected from the User Interface to the Central Control Unit.
1. Check for continuity of the User Interface harness.
2. Check wire harness connections to the User Interface and the Central Control Unit.
3. If the drum is not rotating, unplug the MCU from the CCU (the MI3 or M13 connector). If the code goes away, then replace the MCU. If the code does not go away, replace the CCU.
4. Replace User Interface if drum is rotating.
I believe you need to change the main control board, part # W10133908
That is #14 in This Diagram
That's just been my experience with the F71 and these model washers.