The flow sensor of the Ultimaker S5 signals that filament is not flowing as predicted. The Material Station has not determined end of filament, but something else is wrong with the material flow. The display will show which of the extruders has encountered a problem.

The ER65 message is often an early indication of underextrusion. This can be due to an obstruction in the filament path, or incorrect print settings.

When the ER65 message appears, the print will be paused. You can choose to ignore the error and continue printing, or abort the print. Note that during the paused and printing states, the troubleshooting options are limited. For persistent ER65 messages, it is recommended to stop the print progress and check the extrusion path before reprinting.

There are a few things to try both during and after the print:

During the print After the print

As mentioned above, the troubleshooting options while the print is paused are fairly limited. It is not possible to clean or change the print cores mid-print, as this would affect the print cores' alignment. Before selecting to continue or abort the print, though, please perform the following checks:

Check the feeder lever	Make sure that the lever of the indicated feeder is fully down. If the feeder lever is left up, it will not give sufficient pressure on the filament while feeding.
Check the feeder tension	For Ultimaker materials, the feeder tension should be at the middle mark. If the tension is too high, the feeder may flatten the filament, but if the tension is too low, the material can slip inside the feeder. Use a 2 mm hex key or screwdriver to turn the bolt at the top of the feeder housing to adjust the feeder tension.
Adjust print settings	During a print, it is possible to slightly tweak the print settings. Printing too fast and/or at too low temperatures can cause extrusion problems. Try adjusting the settings via the Ultimaker S5 display before continuing the print job. Note that this is just a quick fix; remember to update the print settings in Ultimaker Cura for the next print job with this material.

After trying the steps listed above, you can select the triangle icon ('play' button) on the display to continue printing. If the ER65 error continues to appear, and underextrusion is visible in the print, it is best to abort the print and try the troubleshooting steps in the second tab.

When the ER65 message appears multiple times throughout the print, there probably is an obstruction in the extrusion path. Resolving this requires aborting the print job and performing some hardware checks.

Clogged print core	A blockage in the print core, even a partial one, can cause extrusion problems. Especially PVA (in the BB core) and composite materials (in the CC core) are prone to cause clogs.  Clean the print core(s) using the hot and cold pull method or swap the print core before retrying the print.
Dirty feeder	After many hours of printing, or when the material has been ground down, there is a chance that there are small filament particles in the feeders. It is recommended to clean the inside of the feeders after three months. Carefully remove the front of the feeder and brush away any filament particles or obstructions according to the cleaning instructions.
Obstructed Bowden tube	Filament strands or particles inside the Bowden tube can prevent the material from passing through smoothly. This extra friction can cause reduced extrusion. Clean the Bowden tubes according to the instructions. Additionally, check for scratches and signs of damage on the inside of the tubes. If any damage is observed, it is recommended to replace the Bowden tube(s).

Tip: The filament path of the Material Station could also be obstructed with filament. For step-by-step instructions (including photos) on how to remove the broken PVA from the system, read the troubleshooting guide on this page.

After performing these corrective actions, you can try the print job again.

Note: In some rare cases, the ER65 message can be caused by a misalignment of the flow sensor magnet in the feeder. For more information, check the expert troubleshooting content below:

Check the rotating magnets of the feeder

The flow sensor has a rotating magnet. The rotations of this magnet are read by the connected PCB and the material flow is calculated in this way. A correct alignment of the magnets is important for a correct reading by the PCB.

In the following pictures, you can see the magnet up close. The aligned magnet on the left picture is in the correct position. In the right picture, the magnet is not fully level. This is causing it to interfere with the PCB, and therefore with the flow sensor readings:

Feeder 2. Magnet is correctly aligned	Feeder 1. Magnet sticks out and is pressed against the PCB.

If your flow sensor is affected by this, please get in contact with support and provide supporting images. A support representative will help you restore full functionality.

Disable the flow sensors

It is possible to disable the flow sensors. This can be a useful temporary patch, especially if the print shows no signs of underextrusion. Open the Settings menu (gear icon) and toggle the switch for Flow sensor to turn them off.

Note that in the standalone S3 and S5 this will also disable the end of filament detection, whereas in the Pro Bundle the end of filament will still be detected by the Material Station. It is still recommended to determine the root cause of the ER65 error, because underextrusion will no longer be detected with the flow sensors disabled.

Need further support?

If the problem still persists after trying all the troubleshooting steps listed above, please contact support by submitting a ticket. For the most efficient help, please share the following information:

• How often the error shows up
• The printer's log files
• Which materials are used
• Print settings (or preferably a Cura project file)
• The outcome of the attempted troubleshooting steps.