I usually have a good crop of runners. This year my crop, too, has been an utter disaster. The problems started early on when they were absolutely infested with blackfly. These pests suck the sap from the stems and really stunt the plants. They never really recovered from that but if they had I don't think my crop would have been too good anyway. Runners hate extreme heat, especially when the flowers are setting fruit. We had a hot spell when that was beginning to happen and the few flowers I had suffered badly. Just one of those things. Tomatoes have been a roaring success this year so you win some, you lose some. That's gardening for you! :-)