Canon PIXMA G5020 Wireless MegaTank Printer - Manual (Page 402)

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Cause
Print head cannot be recognized.
What to Do
A print head may not be installed properly or may not be compatible with this printer.
If you are printing, press the printer's Stop button to cancel printing.
Remove the print heads and reinstall them properly following the steps below. This may resolve the error.
1. Open top cover.
2. Close ink valve.
Tilt the ink valve lever tightly to the left.
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