For any Vesuvius owners that occasionally experience a lack of flow after lifting the grouph ead lever, as it turns out, it was an easy fix. I contacted ACS about the behavior, and they suggested replacing the cam on the inside of the group head, and a pin that sits vertically when disassembling the group head. When I swapped out the old pin for the new pin, I could clearly see that the rubber washer swelled, and was likely preventing water flow, regardless of the pump. Anyway, it was about a 5 minute replacement of the two parts, and all works well now. Sharing just in case anyone else runs into this.
(photo of the old pin, and the swollen rubber washer)
