You can check the total number of pages fed through the printer. The information is printed together with the nozzle check pattern.
Load A4-size plain paper in the printer.
Press the 
button to turn off the printer.
Turn the printer on while holding the 
button down, and then release the buttons when the power light flashes.
You can also check the total number of pages fed from the printer driver.
Windows
Click Printer and Option Information on the Maintenance tab.
Mac OS
Apple menu > System Preferences > Printers & Scanners (or Print & Scan, Print & Fax) > Epson(XXXX) > Options & Supplies > Utility > Open Printer Utility > Printer and Option Information