How to Unclog a Printhead

Some common problems in printers are indicative of print head clogging.  If you are experiencing a decrease in print quality, missing lines or blank pages while trying to print, this may be the issue.  There are many tips on the internet about unclogging the print head.  Such tips range from helpful to detrimental for the printer.  Today, I describe the unclogging process from an ink supplier’s perspective and hope it will be helpful to household users.

The mechanics behind clogging are simple.  The print head is like a water tank with a very tiny opening.  During printing, the machine squeezes out microscopic (picoliter) ink droplets.  The ink is designed to dry fast so as not to smudge.

These are some possible reasons for clogging:

If the print head is exposed to the air for a long period of time, ink can dry up and block the small opening.

Foreign objects (ink impurity or dust) can block the opening.  Some internet instructions advise users to wipe clean the print head with tissues or paper towels, which may introduce blockage to the print head. 

An air bubble can temporarily block the opening.  Air is naturally dissolved in the ink.

Fluctuation of room temperature will change the air concentration and thus form air bubbles.

Changing cartridges also introduces air into the system.  (*Note: This is why you should do a print head-cleaning cycle after installing a new cartridge).

It may not be a blockage.  There are processes that can permanently damage the nozzle; the print head may be scratched and damaged, the print head may have over-heated during a long printing process, or a paper jam may have caused the issue.

It is a common misconception that pigment ink is more prone to clogging than dye ink because pigment ink is in the form of suspended particles and somehow the particles aggregate and blocks the print head.  Pigment ink from reputable manufacturers has such a small size (0.1 µm) that it is almost impossible to block the opening of a print head jet.  This picture shows the relative size of a print head jet opening and a pigment particle (small red dot).  Many dye inks are filtered with 0.22 µm mesh which means the particles in the dye ink are twice the size of pigments.  The particle size of filtered drinking water is about 1 µm.

When you perform the head-cleaning routine, some printers have a suction chamber underneath the print head which will suck the ink out of the cartridge, thus unclogging the blockage.  Some HP cartridges (950, 932) have built-in air bags, which will inflate and squeeze the ink out of the print head, to purge particles and to prevent drying.   There is a small rubber wiper to wipe out excessive ink.

 Try this at Home: Dissolve the Blockage: Just Use Water

 You can use water to dissolve or soften the blockage.   Sit the print head in a bowl of water for few hours.  Most print heads can be submerged underwater as long as you dry up the contact points before inserting back in the printer.

There is a ‘golden rule’ for ink manufacturers:  The ink must be able to dissolve in the medium in which it is made.  That is, the ink must be able to dissolve in ink.  So the best solvent is the solvent that the printer manufacturer used to make the ink.  Many ink manufacturers offer cleaning solution (BCH offers such print head unclogging solution) whichworks with both dye and pigment ink.  If this is not readily available, use water.  In most cases, water performs as well as cleaning solution.

Do not use cleaning solutions that contain corrosive ingredients such as bleach or alcohol, which will increase clogging in pigment ink.  When you search for cleaning solutions, see if the seller also manufactures ink and if the package looks factory-made.  There are cleaning solutions on the market that contain corrosive agents which will temporarily remove the blockage, but then your print head will be permanently damaged because it is corroded.

If not sure, just use water.

Try this at Home: Dissolve the Blockage: Increase the Temperature

Recall from middle school chemistry:

Adding energy (heat) increases molecular motion.

Increased molecular motion competes with the attraction between solute molecules and tends to make them come apart more easily.

Increased molecular motion causes more solvent molecules to contact solute molecules and pull on them with more force, usually resulting in more dissolving.

Since different substances are made from different atoms, increased temperature will affect their dissolving to different extents.

Therefore, you should use hot water when you soak the print head.  The temperature can be somewhere between 90 °F - 120 °F.  In the lab, we use 110 °F water or solution.  There are some websites using fire to heat up the print head.  We are not sure about the practice but want to show you that print heads can tolerate high temperatures.

DON'T TRY THIS!!! Try this.  If you decide to use direct heat, invest in a steaming machine like the one here.  It increases the temperature and the steam will keep printer head moisturized.  Also, you can use it for other housecleaning chores.

Also, Try This: Blow the Ink out by Pushing and Sucking 

Create some pressure to blow the blockage out.

Drill a hole on the cartridge and use syringe to push ink downward

Wash the print head under hot running water

Or, you can create suction from underneath.  Be creative about this.  Some customers showed us the suction chamber they made out of a rubber eraser.  Most hoses can be bought at your local hardware store.  There are some examples of such tools on the web.

Bring it to Next Level: Ultrasonic Cleaner

You may want to invest in an ultrasonic cleaner like the one used in cleaning jewelry or medical equipment.   An ultrasonic cleaner uses cavitation bubbles induced by high-frequency pressure (20–400 kHz) waves to agitate a liquid. The agitation produces high forces on contaminants adhering to the print head.  The ultrasound can be used with just water, but the use of a solvent appropriate for the print head enhances the effect. Cleaning normally lasts between one to three minutes.  Print heads must not be allowed to rest on the bottom of the device during the cleaning process because that will prevent cavitation from taking place on any portion of the object not in contact with water.  Never place the print head directly on the bottom of the unit. It can cause the unit to fail because the parts will reflect the ultrasonic energy back into the transducers. Always allow at least one inch between the tank bottom and the print head for adequate cavitation. Keep the solution within one inch of the top of the unit when the beaker or tray is in place.

If using a tray or basket to lower the parts into the solution, it is better to use a holder that is of open construction (either an open mesh basket or an insert tray) that is adequately perforated for drainage. This also permits sound wave's free access to the parts.

Replace cleaning solution often to increase ultrasonic cleaning activity. Solutions can become contaminated with suspended soil particles, which can settle to the tank bottom and inhibit ultrasonic activity. (When replacing solution, wait 5 to 10 minutes after activating the equipment for fresh solution to degas. This need not repeated with subsequent use, as degassing is required only after the bath is freshly filled).