they are insect polllinated, usually by bees ... how many bumbley-bees have you seen in your greenhouse?!
that & the heat & dryness will account for the lack of beans.
live & learn as they say (or pollinate with a paintbrush!)
You can set runner beans with a very fine rose spray on a hose pipe I'vre done it many times when the late bean flowers really took off and the temps dropped to 50 oF.( bees stop flying in any numbers ) .
Old Mr Digwell gave me that one years ago , so it's back to growing in the green house unless you have trashed them . If you have auto roof vents like I have insects geting in are no problem but for a precaution I have a rabbits tail on a bit of cane to pollinate the tomatoes , capsicums, strawberries and aubergines etc. just incase there are a few areas missed .
I charged it with pollen from two big bunches of supermarket flowers I purchased for my lass and also gave every weed flower in the front garden a wee wipe with it before I zapped them with a hefty dose of round up.