I just went through this myself today. Had the system completely drained, changed out hoses on both pressure and suction/return sides, had air throughout the system. Didn't work real well right off the bat, but enough to get the bucket off the ground and get out from under the awning where I did the work (where it's been for about 4 months). Went through a few cycles on each system, and she's working like a champ within less than 5 (probably less then 3) minutes.