After departing with the Yellow system electric pump deferred; an A320 flight crew returned to departure airport when reservoir pressure to the yellow system was also lost.

Narrative

This trip was the third leg of a re-qualifying check ride for me after returning to the cockpit from a one year medical absence. Prior to departure the Check Pilot and I jointly decided to accept the aircraft with an MEL; Yellow Electric Hydraulic Pump Inoperative. Situational conditions made this a prudent decision in this case. During climb out; ECAM; Hyd Y Rsvr Lo Air PR; displayed. All ECAM procedures and Flight Manual actions were completed. The ECAM contained 'conditional' item that dealt with fluctuations in pressure of the affected system. Initially; this condition was not met but after a few minutes; pressure fluctuations did occur and the conditional item on the ECAM was accomplished.We then decided to return to the departure airport. Consideration was given to a close monitoring of a now isolated Hydraulic system and continue toward our destination; but after a review of current and forecast weather at our destination; the decision to return to our departure airport was made. [It was an] uneventful return to departure airport. All coordination required with Dispatch and others accomplished. ECAM and Flight Manual actions associated with approach and landing accomplished.