Matt Mill wrote:I don't have an answer, but can share a similar experience. I'm growing runner beans for the second time this summer. Last year, mine flowered and dropped the flowers as you describe for a long time before they ever set beans—we might have had a month of flowering before I saw a single bean start to form. This year, it's a little better—I have one bean, last I checked—but the same thing is happening to an extent.
My best guess last year was that it was related to heat. I'm on the southern edge of where runner beans will grow in zone 6b, and I have read they can struggle to set fruit when it's too hot. So depending on where you're located that might be worth considering as a factor. They did eventually set a crop for me, though, so hopefully they will for you too!