Why the HP OfficeJet Pro 6978 Won't Print Black
The HP OfficeJet Pro 6978 is a thermal inkjet printer. When black ink stops printing, the cause is almost always one of three things: depleted ink, a clogged printhead nozzle, or dirty electrical contacts. This guide walks through every fix in order from easiest to most advanced.
Step 1: Check Ink Levels
Before doing anything else, verify the black ink level is not empty.
- Open the HP Smart app on your phone or PC and select your 6978 printer.
- Tap Printer Details or Supplies. The app shows a bar for each ink color.
- Alternatively, press the ink drop icon on the printer's touchscreen to display ink levels directly.
- If the black cartridge is below 10%, replace it before troubleshooting further — you may simply be out of ink.
Step 2: Run HP Print and Scan Doctor
HP's free diagnostic tool often resolves this issue automatically on Windows.
- Download HP Print and Scan Doctor from hp.com/go/tools.
- Run it and select your OfficeJet Pro 6978 from the list.
- Click Fix Printing . The tool checks for driver conflicts, stuck print jobs, and communication errors.
- Follow the on-screen prompts. The tool will restart the print spooler and run a test print automatically.
Step 3: Run a Printhead Cleaning Cycle
If ink is present but black still won't print, the printhead nozzles are clogged. Dried ink blocks the microscopic nozzle openings.
- On the printer touchscreen, tap the gear icon (Setup).
- Go to Printer Maintenance > Clean Printhead.
- The printer will use ink to flush the nozzle channels. This takes about 2 minutes.
- After cleaning completes, print a test page. If black is still absent, proceed to Step 4.
- You can run a second Clean g>Clean Printhead cycle. Do not run more than 3 cycles — excessive cleaning wastes ink without additional benefit.
Step 4: Clean the Printhead Contacts Manually
Electrical contacts between the cartridge and the printer carriage carry the signal that tells the nozzles when to fire. If these contacts are smudged with ink or oxidized, black ink will not print even if the cartridge is full.
- Turn the printer off and unplug the power cord.
- Open the ink cartridge access door. Wait for the carriage to stop moving, then gently slide it to the center.
- Press the tab on the black cartridge and lift it out.
- Find the copper-colored contacts on the back of the cartridge (the small rectangular metallic pads).
- Dampen a lint-free cloth or coffee filter with distilled water (not tap water — minerals leave residue).
- Gently wipe the copper contacts in one direction. Do not scrub back and forth.
- Also wipe the matching contacts inside the printer carriage using a fresh part of the cloth.
- Allow both sets of contacts to air dry for 10 minutes before reinserting the cartridge.
- Print a test page after reinserting.
Step 5: Re-Seat the Black Cartridge
A cartridge that isn't fully clicked into its slot won't make proper contact with the carriage.
- Remove the black cartridge completely.
- Check that the small locking tab on the cartridge is not bent or broken.
- Push the cartridge firmly back into the black slot until you hear and feel a distinct click.
- Close the access door and print a test page.
Advanced Troubleshooting: Extended Cleaning
If a standard clean cycle did not clear the clog, try the Extended Cleaning procedure. This pushes a much larger volume of ink through the nozzles to dislodge stubborn dried ink.
- On the touchscreen: Setup > Printer Maintenance > Extended Cleaning.
- This process takes about 5 minutes and uses a significant amount of ink.
- After extended cleaning, run an alignment page: Setup > Printer Maintenance > Align Printhead.
- Print a diagnostic test page to verify results.
If even Extended Cleaning does not restore black ink output, the printhead is permanently clogged or electrically failed. At this point, replacing the black ink cartridge with a fresh genuine HP cartridge (not refilled or remanufactured) is the recommended next step, as sometimes what appears to be a clogged printhead is actually a defective cartridge with a blocked nozzle array at the factory.
Frequently Asked Questions
Can I use third-party or refilled black cartridges in the OfficeJet Pro 6978?
Technically yes, but HP's firmware actively works against third-party cartridges. The 6978 may display a "non-HP cartridge detected" warning, or it may silently refuse to print black after a firmware update.
The nozzle check pattern shows black nozzles are missing — what does that mean?
A nozzle check pattern (Settings > Reports > Nozzle Check Pattern) shows which nozzles are firing. If you see white streaks through the black section of the pattern, those specific nozzles are clogged.
My 6978 prints perfectly in color but not black at all — is that a printhead or a cartridge issue?
When color prints but black does not, the issue is 100% isolated to the black ink system — either the black cartridge, the black-channel printhead nozzles, or the black carriage contacts. Start with a fresh genuine black cartridge and clean contacts as described in Step 4 above.
How do I know if the printhead itself (not the cartridge) needs replacing?
On the OfficeJet Pro 6978, the printhead is integrated into the cartridge. You cannot replace the printhead separately.
When to Contact HP Support
If you have tried all the steps above including replacing the black cartridge and the printer still won't print black, the issue is likely a hardware failure in the carriage assembly. Contact HP Support at support.hp.com or call 1-800-HP-INVENT.
If the printer is within its 1-year warranty, HP will repair or replace it free of charge.
