When your printer is in Offline mode, you need to press the Start/Stop button to set it to Ready mode, so that it can print your data. Further reading from your printer manual, page 23,
link:
ftp://download.epson-europe.com/pub/download/3271/epson327143eu.pdf
Most printers automatically go to Offline mode when they haven't been used for some time to conserve power. I keep my printer completely turned off and when i do need to print something, i'll turn it on. How long that timeout period for your printer is, that i don't know since i don't get paid enough to go over all the 167 pages in your printer's manual.