If one of the main hydraulic pumps fails there is an automatic valve which opens to supply both systems from the good pump.
This is intended to temporarily minimise the effect of a sudden failure, extended use can cause the good pump to overheat and raise an alarm. They carried out the correct action which is to disable the transfer valve and allow the good pump to cool down.
I only hope you meant: this "valve" as the PTU, correct?
Colocolo