Hi. The 140CR normally does not have a thermal printer. It uses a drum printer with an ink roller. Either way, it sounds like you have a faulty printer. These machines are usually quite reliable until the printer wears out, then they show exactly the symptom you describe. It would be best to get it checked by a dealer.
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If anyone needs more information, the Casio 140CR manual can be found at C-tech here:
http://the-checkout-tech.com/manuals/cashregisters/Casio_140CR_user_manual.html
Registerman, July 2011