Digital BW, The Print

I doubt it is the ink. It sounds more like a problem with the way the 
tubes are arrainged. Warming the tubes makes them more flexible, and 
might temporarily allow ink to flow, but when it cools might close 
again. Have you sent an email to Ink Republic yet?

Since this isn't really a technical group, I would suggest that this 
discussion be taken to the printers and printing forum at 
http://forums.dpreview.com/forums/forum.asp?forum=1003 There are a 
lot of Ink Republic users there, so one of us should be able to help. 
You might want to take a picture of the tubes and "carts" to help see 
if there is a problems. The other thing you might want to look at is 
if the printer top cover is pinching the tubes, try printing with the 
cover open, and don't ever use the tubing clamps to lock off the 
lines, this can cause a permanent crimp in the tubing if they are 
left clamped for too long.