What was found
(CAN) NR 1 HYDRAULIC FLUID HOT CAUTION MESSAGE ON CLIMB OUT, FOLLOWED SHORTLY BY A NO 1 HYDRAULIC PUMP CAUTION MESSAGE AND COMPLETE LOSS OF PRESSURE, QUANTITY REMAINED NORMAL, HOWEVER THE TEMP INCREASED STEADILY. AIRCRAFT RETURNED TO DEPARTURE AIRPORT. CASE DRAIN DIFFERENTIAL PRESSURE BUTTON FOUND POPPED, BOTH CASE DRAIN AND PRESSURE FILTERS FOUND CONTAMINATED. TEMP INDICATORS FOUND TO HAVE REACHED 300 DEGREES F. AIRCRAFT SYSTEM WILL BE FLUSHED AS PER AMM, PUMP WILL GO BACK TO OEM ON PARTS EXCHANGE PROGRAM.