Cleaning a printhead

Inkjet printers are a fantastic invention however they can be problematic if they are not used regularly or correctly. Most users will automatically blame the ink cartridge if there's a printing defect however the truth is that it is almost never the cartridge at fault.

Let's take a detailed look at the inkjet printhead and discuss the causes of printhead clogging and the cleaning solutions. We will also discuss ways in which you can prevent your printhead from clogging in the first place. The image to the left is of a typical Canon printhead. This is what they look like with the cartridges removed and the individual nozzles exposed.

The Canon Printhead Explained ( Thermal Printhead )

The Canon printhead is whats known as a "Thermal or Bubblejet Printhead". It uses thousands of micro size resistors in each colour nozzle to heat up the ink and literally spit it out onto the paper. As the ink rapidly heats up due to the increased temperature of each resistor it creates a series of bubbles. This is much the same effect as boiling any type of liquid and seeing the rush of bubbles coming to the surface and releasing the expanding oxygen.



Once the bubble gets hot enough and explodes and has spat the ink onto the paper the air starts to cool down as it rushes in to replace the expelled air from the bursting bubble. In turn it starts to suck more ink into the minute nozzle and again starts heating it until it also explodes. This process continues at a very high rate until eventually the image is fully printed. The higher the print resolution the more nozzles are used. Printhead cleaning cycles utilize all of the nozzles.



As the printing  process continues ink is continually drawn into the printhead nozzles and the void or vacuum that is left after the bubbles explode continues to suck ink from the cartridges into the printhead.

The amazing fact is that each printhead nozzle is actually smaller in diameter than a human hair. This is the reason that a printhead can be prone to clogging.

The Epson Printhead explained ( Piezo Printhead )

The "Piezo Electric" Printhead as it is known is what all Epson printers use. It uses an entirely different process to the thermal printhead in that it doesn't heat the ink but actually uses an element which kind of acts like a micro pump to push the ink out onto the paper.

Many people love the piezo printhead as it is capable of producing much higher print resolutions. This is achieved due to the Piezo head being much more finely controlled and the ink flow being able to be adjusted far more accurately than the thermal printhead. The biggest drawback is the fact that the Piezo printhead is far more prone to clogging or blocking up with Ink.

The diagram to the left shows how the Piezo printhead works. A charge is applied to the piezo electric element above each nozzle which causes it to bend forward.

This creates a pressure behind the element which draws ink into the nozzle chamber ready for printing. Next step is to actually push the ink out onto the paper surface.


To actually push the ink out through the print nozzle we now have to get the element to move in the opposite direction to force the ink out of the nozzle and onto the paper. To do this the charge to the element is simply reversed so instead of pulling away it now pushes towards the print nozzle and forces the ink out of the tiny opening and onto the paper.

As with the thermal printhead the entire process is electronically controlled from the printers firmware which tells the printer exactly what to do.

An overview of the operation of a Printhead

Hopefully you are not totally confused after reading about the printheads operation. A printhead whether thermal or piezo basically operates as follows. The ink cartridges all sit directly above the printhead, each colour above it's corresponding print nozzle.

When we hit the print button an electronic signal is sent to the printer and once it gets to the printing stage the above processes take place. Each colour nozzle is either turned on or off to print minute coloured particles according to the electronic signal which contains all of the complex orders for the print nozzles to follow.

The 3 main colours Cyan, Magenta and Yellow as well as the black all print minute dots as required and similar to a TV they all combine to form the various colours and complete the printing of the image. What an amazing fete to know that this incredibly complex process all takes place within seconds and how dare we get angry when the printing goes pear shaped ( HaHa ).

So now that you are an expert on the operation of an inkjet printer lets take a look at why printheads clog up and some tips on preventing this from occurring. 

Why does a printhead clog or block up

There are numerous reasons as to why printheads block. The actual cause of the blockage is that ink dries or congeals inside or on the outer surface of the printhead. Due to the microscopic size of the print nozzles (smaller than the diameter of a human hair) they can quite easily become blocked. Blockages usually show up as either gaps or lines in the printing, incorrect colour or in the worst cases no print at all.

Certain printers are known for clogging. Epson are the leaders in clogging as the nozzles are very small to achieve the high print resolution and they are just known for clogging up. Brother printers have a common issue with the Black nozzle clogging. As to why this occurs no one seems to know.

Here are the main causes of printhead clogging:

Lack of printing - If the printer sits around for long periods of time the ink can dry inside the printhead and result in clogged nozzles.

Not changing cartridges when prompted by the printer -  this is also a leading cause of printhead clogs. If you print for too long on a near empty cartridge you will start introducing air into the printhead which in turn helps dry any remaining ink inside the printhead and results in clogged nozzles. 

Using low grade generic cartridges - low grade cartridges with the wrong ink viscosity can also quickly clog the printhead. Make sure that you purchase your non genuine cartridges from a reputable source.

Dirty or faulty purge pump or pads -  If your printer has very dirty pads on the purge pump then the printer will be unable to effectively run cleaning cycles. During the automatic cleaning cycles that your printer does periodically large amounts of ink are sucked through the printhead and out into the waste pad. This helps to clear any dried ink or residue that may cause printhead blockage. If either the pump is faulty or the pads very dirty then little cleaning occurs and blockage is highly likely.

Cartridges not breathing correctly -  If one or more cartridges do not have the breather tape fully removed then the ink will not flow properly from the cartridge and into the printhead.

And finally - How to clean a printhead

For printers with a removable printhead the easiest cleaning method is to remove the printhead and flush it ( from the cartridge side ) under a hot water tap. This is the easiest method for earlier Canon printers which have removable printheads. Keep the water gently flowing until all of the ink is flushed out and the water comes out clear. If the blockage still occurs you will need to soak the offending nozzles in a printhead cleaning fluid.

For printers without a removable printhead you will need to open the printer as if you were going to change inks. When it comes to the rest position and is accessible quickly pull the power chord out so that the printhead remains in an easy position to work on.

If possible lay some blotting paper folded and soaked in cleaning fluid under the printhead carriage and then move the printhead over the top of the blotting paper. This helps to clean the outer surface of the printhead. You can gently run the printhead carriage back and forth over the blotting paper to help clean the printhead surface. Next insert around 2-3 ml of cleaning solution into each of the clogged nozzles and allow it to soak for an hour or so.

After this you can replace the cartridges, run a printhead clean and then see if the problem has been solved. If not you may need to repeat the process and let it soak for a longer time.

If a certain colour is clogged you can try putting the printer into its highest resolution print mode and try to print a full page of that one solid colour. This is basically the same method your printer uses when performing individual nozzle cleans. 

 It is extremely common for a printhead nozzle to become blocked immediately after replacing one or more cartridges. There are several reasons for this such as air getting introduced into the nozzles, excessive ink pumped into the nozzles straight after a cleaning cycle or the purge pads partly or fully blocked. This prevents the purge pump from properly sucking the ink from the new cartridge into the printhead therefore appearing as a partial or full blockage of certain nozzles.

Cleaning the purge pads on your printer

The purge unit is usually situated on the right hand side of the printer underneath the printhead carriage rest position. The image to the left shows a typical Canon purge unit with a colour sponge and a Pigment black sponge.

These sponges are surrounded by a rubber edging which forms a tight seal against the printhead which helps the purge pump to suck ink through the printhead during cleaning cycles. This excess ink is pumped directly into the waste pad below the printhead carriage. To test if the purge unit is working correctly you can fill each pad with a few ml of cleaning fluid until you can see a small pool form. If this pool of fluid leaks away within a few minutes then there is an issue with the purge unit. ( a leak )

Close the printer and let the printer run a cleaning cycle. Open the printer back up and check that the fluid has all gone. If the purge unit is working correctly then the fluid will all be gone as the pump will have sucked it all up and into the waste pad below.

Many older printers have faulty or dirty purge units and this is often a major cause of printhead clogging. Make sure that you check the purge unit if you cant seem to unblock the print nozzle and keep it clear.

Another thing you can check is that the rubber surrounds around the purge pads are not damaged or distorted. If they are not firmly sealing against the printhead then the pump will not work correctly. If they are only distorted sometimes you can reshape them a little by gently pressing them into shape with a pencil etc. 

Types of printhead cleaning Solutions

There are various types of cleaning solutions on the market and they vary greatly in their effectiveness. Many are purely detergent based which is okay for cleaning printers using generic ink as all generic inks are water based. For genuine ink blockages a more aggressive solution is needed.

At Ink Hub we have experimented with various solutions and our current formula is from a company called "Sensient" and we have simply added about 10% of Aqueous Ammonia to give it a bit more of a kick. As much as I don't like using ammonia it seems to have a better ability to break down dried ink.

Useful Links

Cleaning Purge Pads in a Epson Printer

Cleaning Brother Printheads

Cleaning a clogged Epson Printhead

Cleaning clogged Epson nozzles the easy way