Since the PTU comes on when the differential in a 3000psi nominal system is 500 psi, and the direction is automatic, then more has to be wrong for there to be such low pressure on one side such that both the PTU is working and it has low enough load for it to overheat.
What is that "lot more that has to be wrong"?
Obviously if G is leaking, you don't want to be pumping fluid over. But if everything else is OK, it doesn't happen. What else has to fail?
PBL