HP Error 21 — What It Means & How to Fix It

Updated July 2026 · Independent PrinterCare USA support guide

Error 21 is one of the most frustrating errors HP LaserJet users encounter because it stops your print job dead and often appears without warning. This error specifically indicates that a single page contains more data than your printer's RAM can handle, which usually happens with complex graphics, high-resolution images, or documents with multiple fonts and overlapping design elements.

The good news is that error 21 is almost always fixable without calling a technician, and most solutions take less than fifteen minutes. We'll walk you through the most effective fixes, starting with the simplest document adjustments and moving toward printer settings that resolve even the most stubborn cases.

How to fix it — step by step

1. Restart the Printer Completely. Power off your HP LaserJet printer using the physical power button and wait for at least thirty seconds while it fully shuts down. Turn it back on and allow it to complete its startup cycle, which typically takes one to two minutes. This clears the printer's memory and often resolves temporary processing errors that trigger error 21.
2. Reduce Image Resolution in Your Document. Open your document in Word, Adobe, or your design software and select all embedded images. Right-click and choose compress or resize options, targeting 150 to 200 dots per inch instead of the original high-resolution settings. Even reducing image quality slightly can cut the page data by fifty percent or more, eliminating the complexity that triggers error 21.
3. Remove Unnecessary Fonts and Formatting. Simplify your document by limiting fonts to no more than two or three typefaces and removing decorative elements like drop shadows, gradients, and transparency effects. These design elements significantly increase the data processing required per page. Save and attempt to print again after making these changes.
4. Clear the Printer's Hard Drive Memory. On your HP LaserJet, navigate to the settings menu using the printer's touch panel or physical buttons, find Device Settings or Maintenance, and select Clear Hard Drive or Reset Memory. Confirm the action when prompted. This removes any cached data or incomplete jobs that might be consuming printer memory.
5. Update the Printer Firmware. Visit HP's official support website, enter your exact printer model number, and download the latest firmware version available. Follow HP's step-by-step firmware update instructions for your specific model, which typically involve downloading a file to your computer and following on-screen prompts. Firmware updates often include improvements to page processing and memory management that directly address error 21.
6. Increase Printer Memory if Available. Check your printer's specifications to determine if it accepts additional RAM modules. If your model supports memory upgrades, adding four gigabytes of RAM is a permanent solution that allows the printer to handle more complex pages. This requires opening the printer and installing the module, or you can request professional installation for approximately forty-nine dollars.
7. Split the Document Into Smaller Pages. If the error persists and the document is critical, try printing just the problematic pages separately or break your design into multiple smaller files with fewer elements per page. This temporary workaround allows you to complete your print job while you troubleshoot the underlying cause.
8. Contact HP Support or a Technician. If error 21 continues after all previous steps, the printer may have a hardware issue with its memory modules or processing board. Schedule a remote support session through HP's website for thirty-nine to forty-nine dollars, or contact a local printer repair technician who can diagnose hardware problems and perform repairs.

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