Preparation for shortest walk by only leaving the the biggest curve ''network''

So I have a big curve structure that is made from lines touching each other at end points, I want to do shortest walk on it but I get this error. 1. No walk found for line at position 0. Are end points isolated? At first I thought that my search path has to begin at end points, but then I realised its due to some artefacts that do not connect to the biggest ''curve network'' but there is an existent smaller one. So the question is how would one cull these curves? I don't think I am able just to join them and measure the length because curves do not join with T junctions.