Why is our brand new dishwasher not draining?
You say that the drain hose runs down to the crawlspace then back up again.  It's winter time (at least in the northern hemisphere); I wonder if the water is freezing in the drain hose at the lowest point, enough that hot water from the dishwasher isn't able to reach it to melt it (there would likely be a layer of cold liquid water between the dishwasher and the bottom of the hose).

I think it's odd that the drain hose feeds through the crawlspace; any installations that I can remember seeing have a hose feeding through the cabinet wall to the sink's plumbing.  Is the dishwasher adjacent to the sink so that you could redirect the hose like that?