Printer keeps printing double-sided even with duplex turned off

[Si415]

When Letterhead paper type is selected, printer always prints double-sided even with duplex turned off on the printer and printer preferences. 

[sandytechy20]

@Si415

Welcome to HP forums.

Update the printer firmware

Refer this HP document for the steps to update the printer firmware:- Click here

When you set up a duplex printing job, the settings might carry over to the next print job. Additionally, some HP printers come with duplex printing set as the default. To change back to one-sided printing, turn off the duplex setting in the print window.

To preserve duplex or one-sided settings for future print jobs, complete the print job with the desired settings, click the Presets menu, select Save Current Settings as Preset, and then give the preset a name such as One-Sided Documents.

Let me know if that helps.

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Cheers.