Netsys HWS pipe sizing

Hi i wonder if anyone has any suggestions, 

I'm currently sizing hot water F&R  for a 3 story building, However 1 pipe is massively over sized.  Its happening on section 19 return pipework between floors. I've tried changing the draw pipe heights and right clicking on the pipe using fix/unfix etc but cant seem to pinpoint the pipe to change it.

Could you provide a link so that I can upload my model for checking?