Detecting whether a design is 'impossible' or not is difficult as exchangers can sometimes cling onto tiny scraps of heat.. I'll look over the design and see if I can tweak the detection to fix it.
Edit: I made the 'Impossible' detection a bit more lenient and swated a bug in the Effective EU/t code --> Fixed! (Note the time limit is set to 250 ticks)
Edit 2: Time Limit bug squished too, heh.