When a Thermal receipt printer won't stop printing garbage, there are two things to try:
1. Perform a Power-cycle + Feed
This is done by first turning off the printer. Next, hold the feed button down. while continually holding the feed button down, turn the printer back on. This should print a receipt out. After the receipt prints, press the feed button one more time. A receipt with random characters will print out. Try printing again to that printer to see if garbage still prints out.
2. Perform an Open-Close-Feed
This is done by pressing the button on the top of the printer to first open the lid of the printer. Next, tap the feed button. Finally, close the lid of the printer back up. This must be done in quick succession to be effective. After closing the lid, a receipt should print out that displays information about your printer. This receipt can also be helpful in finding the IP of your Thermal printer.
See the attached document for pictures of what the receipts that are printing out should look like.
Note: The version number as well as other information may vary slightly from those receipts contained in the attached document.