Canon S400 Reference Manual page 182

Check 1
Is the print job a finely detailed photograph or illustration?
The printer requires more time to process a finely detailed illustration or
photograph. Check the POWER lamp. If the POWER lamp is flashing
green, the computer is sending print data to the printer and the job is exe-
cuting normally.
If the print job requires using a large amount of black ink on plain paper, the
print job may require more time.
Check 2
Has the printer been operating for a long time?
The print heads may occasionally overheat during a long print job.
If the print head overheat, printing pauses at the end of a pass across the
page to allow time for the print head to cool and then restarts after a brief
interval. Interrupt printing at a convenient point, switch the printer off and
wait for at least 15 minutes for the print head to cool.
If the printer overheats while printing a densely coloured photograph or
illustration, the printer may beep and stop printing to protect the print head.
In this case, you cannot continue printing. Switch the printer off and wait at
least 15 minutes for the print head to cool.
To avoid minor burns, never touch the print head or the surrounding area.
Caution
Troubleshooting - Printer Does Not Start or Stops in Mid-job
Printing halts
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