If your HP Smart Tank 720 printing lines are ruining documents and photos with unwanted horizontal or vertical streaks, you're dealing with one of the most common inkjet printer problems. This issue typically stems from clogged printheads, air bubbles in the ink lines, or alignment problems—especially common in tank-based systems like the Smart Tank 720 where ink flows through tubes from reservoirs to the printhead. The good news: most causes can be resolved at home without professional printer repair. This guide walks you through proven troubleshooting steps to fix printer output and restore clean, professional-quality pages.
Identifying the Type of Lines on Your Prints
Before you start troubleshooting, examine your test page closely. Horizontal lines or banding usually indicate clogged nozzles or air gaps in the ink delivery system. Vertical lines often point to printhead alignment issues or physical debris on the encoder strip. White lines running through dark areas typically mean specific color channels aren't firing. Note which colors are affected—this helps isolate whether you need to clean the black printhead, tri-color printhead, or both.
Step-by-Step Troubleshooting for HP Smart Tank 720 Printing Lines
1
Run the Automated Printhead Cleaning Cycle: On the printer's touchscreen, navigate to Settings > Printer Maintenance > Clean Printhead. Select "Level 1" cleaning first. The Smart Tank 720 will push fresh ink through the nozzles to dislodge dried ink. Print a diagnostic page afterward by going to Settings > Reports > Print Quality Report. If lines persist, run Level 2 cleaning— but avoid more than three consecutive cleanings to prevent ink waste and potential printhead damage.
2
Purge Air Bubbles from the Ink Lines: Tank systems like the Smart Tank 720 are prone to air bubbles after refilling or if the printer sits unused. Open the ink tank lid and gently tap the ink tubes where they connect to the printhead carriage. Then run the "Prime Ink System" function found under Settings > Printer Maintenance > Prime Ink. This dedicated HP Smart Tank 720 function forces ink through the entire delivery path, eliminating gaps that cause printing lines. Listen for gurgling sounds—this indicates air is moving out.
3
Manually Clean the Printhead Contacts and Nozzles: Power off and unplug the printer. Open the cartridge gate, wait for the carriage to center, then unplug to prevent movement. Lift the printhead latch and remove both the black and tri-color printheads. Dampen a lint-free cloth with distilled water (never tap water or alcohol) and gently wipe the copper electrical contacts and the nozzle plate. Let components air-dry for 10 minutes before reinstalling. This direct contact cleaning resolves about 40% of persistent line issues in HP printer support cases.
4
Align the Printhead Using the Built-In Tool: Misalignment causes vertical lines and color registration errors. Go to Settings > Printer Maintenance > Align Printhead > Automatic. The Smart Tank 720 prints an alignment page, scans it internally, and adjusts firing timing. For stubborn cases, select "Manual Alignment" and follow the on-screen prompts to choose the sharpest patterns from printed samples. Re-align after any physical printer relocation or paper jam removal.
5
Check and Clean the Encoder Strip: The clear plastic strip behind the printhead carriage tracks position. A speck of ink or dust here causes vertical lines and erratic carriage movement. Power off, then gently wipe the entire strip width with a cloth lightly moistened with distilled water. Move the carriage manually to access the full strip. Never pull forcefully—the strip is tensioned and expensive to replace. This step is frequently overlooked in basic troubleshooting guides but critical for tech support resolution.
6
Verify Ink Levels and Refill Tanks Properly: Low ink triggers air intake at the tank bottom. Check all four tanks (black, cyan, magenta, yellow) through the transparent windows. If any tank is below the minimum line, refill with genuine HP GT53/GT52 ink bottles only. When refilling, keep bottles upright and wait for the glug-glug sound to stop completely—tipping bottles introduces air. After refilling, wait 15 minutes for ink to settle before printing. Third-party inks often cause compatibility issues that manifest as printing lines.
⚠️ Important: Never perform more than three consecutive printhead cleaning cycles without printing between them. Excessive cleaning overheats the printhead, wastes significant ink, and can permanently damage the thermal inkjet firing chambers in your HP Smart Tank 720. If three cleaning cycles don't resolve the lines, allow the printer to rest for 6 hours—dried ink often softens naturally and clears with normal use.
Preventing Future Line Issues
Print at least two pages weekly to keep ink flowing and prevent nozzle drying. Use the printer's "Sleep Mode" rather than unplugging it, as occasional automatic maintenance cycles keep the system primed. Store the printer in a climate-controlled environment—temperatures below 59°F (15°C) or above 95°F (35°C) accelerate ink viscosity changes. When replacing printheads, use only HP 316/317 series printheads designed specifically for the Smart Tank 720/750/790 family.
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Why does my HP Smart Tank 720 print lines only in color documents?
This indicates the tri-color printhead (cyan, magenta, yellow) has clogged nozzles or air bubbles while the black channel remains clear. Run printhead cleaning focused on the color printhead, or remove and manually clean it. Also check that the color ink tanks aren't low, as depleted cyan or magenta specifically causes banding in mixed-color areas.
Can using non-HP ink cause printing lines on the Smart Tank 720?
Yes. Third-party inks often have different viscosity and drying properties that clog HP thermal inkjet nozzles faster. Some formulas also lack proper surfactants, causing poor drop formation that appears as lines. While genuine HP GT53/GT52 ink costs more, it matches the printhead's thermal firing characteristics and includes anti-clog agents that extend printhead life significantly.
How do I know if my Smart Tank 720 printhead needs replacement rather than cleaning?
If you've completed all six troubleshooting steps above, waited 24 hours, and lines persist across multiple document types, the printhead likely has permanently damaged nozzles. Check your page count—original printheads typically last 10,000-15,000 pages. Replacement HP 316/317 printheads are user-installable and cost less than professional printer repair service. Install a new printhead and run initial setup calibration before judging results.