Runner bean flowers that fall off and fail to produce pods are likely suffering from adverse weather conditions, damage or poor irrigation, according to the Royal Horticulture Society. This tends to happen early in the season rather than later.
Infrequent harvesting, insect damage, bird damage, bad weather conditions and infrequent irrigation are common problems in runner beans. To help get pods to set, lime the soil if the soil pH is under 6.5. Mulching is another way to help set pods on runner beans. Also, give the beans shelter from the weather, and water them during any dry spells. Rotate the plant crops to yield more beans.