Just back tracking a little on this subject. If a hyd pump has gone bad, then you need to change out the fluid and filter. On a variable speed pump, there is a charge pump that keeps the main pump full and pushes the fluid through the pump case to help cool it. On my VSP pump, we have a bleed screw and hose that we use to expel air. We do this by disabling the engine from starting, and turning the engine over for about 10 sec at a time to expel all the air out of the pump and hoses. Your procedure may be a little different, but you have to find a place to let air out , and perhaps install a hyd gage in the pump circuit. If the pump is above the reservoir, it will not prime itself.