HP Fusing Assemblies and Envelope Printing

Recently, I’ve seen a rise in calls related to envelope and fusing problems. I see issues with fusers from all makes and models of printers but for the point of this article I’m going to focus on HP fusing assemblies.  In this post we’ll review different types of fusers, toners, and envelopes. Given the wide variety of options many different print quality issues can arise and will vary with your printer model.

HP Fusing Assembly History

When I first started working on HP machines back in the late 90’s, the majority of the HP fusers I saw used old technology. The fusers consisted of thermistors, thermal fuses, hot roller, pressure roller, and halogen lamps. They were very reliable, durable, and typically lasted long past their intended life. Getting a label stuck in the fuser simply required the user to remove it. Running a paper clip or staple through it might cause a nick but no serious damage. Envelopes would wrinkle up in the back if not fed properly. Actually, the envelopes would always wrinkle, but a lot less when the envelope tabs in the fuser were set to release some of the pressure. This is the case on models like the HP 5si, 8000, and 8100 series.

The new fuser technology, found first in models like the HP 4L and 4000 series, use a heating element, pressure roller and fixing film. The benefits were that these fusers would use less energy,  heat up more quickly, feed envelopes better, and for HP, they are easier to damage so users would have to replace them more often.

The downsides to these new fusers were that they’re easy to damage, they weaken over time, and envelopes can damage the fixing film surface. Heck, just about anything except for plain paper can have a negative impact on them! Plus the new fusers have to be replaced more often than the old technology.

Today, newer fusers like those in the HP 4250 and P4015 have added a metal coating on the inside of the fixing sleeve that has added more durability and fuser modes that step up the heat in the fusers. But problems still occur with heavy envelope usage.

Wrinkled Envelopes

Without going into a lot of detail, fusers use heat and pressure to bond the toner to the paper. When thinking about envelopes you have two pieces of paper with air trapped in the middle. When the envelope hits the fusing assembly in models using the old technology, the top layer of paper, with all the pressure, likes to slip a little, resulting in wrinkles. In some cases these wrinkles can get really bad. So what HP and other manufactures have done is to lower the speed of the feed of the envelopes and they have put envelope tabs in the back of the fuser. When you lower these tabs some of the pressure is released inside the unit resulting in envelopes feeding through better.    It’s important to change these tabs back after you’re done using envelopes or you could have print quality issues and, with long term usage, fuser damage.

It’s vital to make sure the settings on the printer’s control panel are set properly as well as the settings inside the print driver on your computer.  Note: On most Lexmark printers you will not see envelope tabs.  Lexmark printers have solenoids in the back of the fuser that accomplish this task so you only need to make sure your setting on the printer and computer are right.

And, be aware that printer models in which the fuser has the fixing films don’t tend to have envelope wrinkle problem because of the technology so you will not find envelope tabs on these machines.

Envelope Settings for Fusers

If you have problems finding where to change your printer’s settings go to the information menu and print off the menu map. This shows the control panel menu structure so you can find the settings you want to change.

Printer Settings

On the HP 4000 series make sure you have the Small Paper Setting set to ‘small’. The default setting is ‘normal’. This will prevent abnormal wear on the fixing film down the left side middle.

On later models you have fuser modes. Just make sure the fuser mode for envelopes is set ‘high 1’ or ‘high 2’.  This slows the paper down as it feeds through and bumps up the fuser temperature. Also, on models like the 4200 when you put an envelope in the MP tray it first asks the size then it ask you the type. It’s important to the machine that the type is envelope. If not then it will feed it through on normal settings and not apply more heat to the fuser.

Computer Settings

When printing from software you need to make sure that you set the paper size and type correctly. Once again it’s very important to have the type right. If you set the type on the printer but not on the computer, one will display an error message informing you that the settings don’t match up.

Toner and Envelopes

Lately I’ve seen more of this problem, where the toner doesn’t properly bond to the paper and smears off. When that happens, and after you’ve verified you have the printer and computer settings configured correctly, check the toner.  All toner is not the same. Brother does a good job of showing this when you install a new machine. They show you a magnified picture of their toner particles compared to some rebuilds or third- parties. Brother toner particles are all nice, neat, look like little marbles, and are very small. The others are large and look like a bunch of rocks. Same goes with HP, Xerox, and other manufacturers. This is what gives them the high dpi and ability to feed and bond the toner to the paper at such high speeds.

Like anything else, the larger the size the longer it takes to heat up. So cheap, third-party toner takes longer to reach temperature or requires a higher temperature to heat it fast enough to bond to the paper. Typically it doesn’t matter as much on plain paper but when you get into envelopes and card stock the problem with the cheap, third-party toner shows up quickly. When in doubt, go with an OEM toner.


Make sure the envelopes meet printer specifications. Companies love to use special envelopes that have texture on them. If in doubt just find a regular plain envelope and try that before you get all crazy and start replacing parts.

HP OEM Fusers and Rebuilds

On some models envelopes will wear down the middle of the fuser’s fixing film and cause print quality problems. Models like the 2100 and 4000 series are famous for a gray line running down the middle of the page where the upper lip of envelopes had worn away the top coating on the fixing film. As mentioned previously, it’s important to set small paper to ‘slow’ on the 4000 model to make the fusers last longer.

As fusers that have fixing films age the heating element gets scratches on it and other parts start to wear out resulting in lower fuser temperatures. When companies rebuild fusers they check the heating element under normal printing conditions — not under special circumstances like envelopes and card stock. I know, because I’ve asked a few.  These companies will keep using these heating elements over and over till they go out, usually on your watch. So after you have checked everything else and verified everything is the way it should be then it’s time to try the fuser.

Note : Verify the power source. Make sure it’s plugged into a wall outlet and not a surge arrest. Too many devices on the same outlet could draw the power down on the printer resulting in poor fusing because of temperature problems.

Other Tips for Printing Envelopes

Never use envelopes with plastic windows or adhesive tape on the envelope flap. They will melt in the fusing assembly.

Inform your customers or end users that heavy envelope usage will result in premature fuser replacement. Trust me they will not last as long.

An alternate to printing envelopes is to print labels then apply them to the envelopes. The only downfall to this is that if you print off one label at a time then reuse the sheet of labels over and over the labels will get discolored. If you feed paper over and over through these machines they get a gray background to them. So that’s my warning. If you see this happen on your labels you know it’s because of over usage of the label sheet. This doesn’t usually cause a problem but picky customer can find this annoying.

Personally, I’ve gotten to the point of recommending other machines than HPs if the customer tells me they are going to run heavy amounts of envelopes and other special paper through their machines. For plain paper printing you can’t beat an HP.

However, for special printing I would recommend a Lexmark printer because they still use the halogen lamps and hot rollers, which tend to be more durable than fixing films.

Kevin Gumpp is a certified printer technician and freelance writer for Market Point. If you have a question regarding this topic or have any other printer repair related questions or topics for which you would like more information, please send an email to maryp@marketpoint.com.

One thought on “HP Fusing Assemblies and Envelope Printing

  1. Pingback: HP CLJ CM3530 print defect, is it a failing fuser?

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