The red sensor light is stuck on red. I have cleaned the filters. What might be the problem?

It sounds like there may be a problem with the vacuum's sensor that detects when the bag or filter is full. Here are some troubleshooting steps you can try to fix the issue:

1. Check the bag and filter: Make sure that the bag and filter are properly installed and not damaged. If the bag or filter is damaged or not properly installed, it can cause the sensor to malfunction.
2. Reset the sensor: Some Nilfisk vacuums have a reset button or switch that can be used to reset the sensor. Check the owner's manual or the vacuum itself for a reset button or switch and try resetting the sensor.
3. Clean the sensor: Dust and debris can sometimes accumulate on the sensor and cause it to malfunction. To clean the sensor, turn off the vacuum and unplug it from the electrical outlet. Locate the sensor and use a small brush or compressed air to carefully clean it.

If these troubleshooting steps do not resolve the issue, it is possible that the sensor itself is damaged or malfunctioning. In this case, it may be necessary to have the sensor repaired or replaced by a professional.

check to make sure the settings didn't get inadvertently switched to the hi position, move the switch back and forth from high to reg a few times, then leave it on reg.

remove and hand wash the primary filter and secondary filter, dry throughly and replace them in the vacuum.

if none of this works, you will need to have the vacuum serviced, or if it is still working, just don't pay attention to the dirt-finder. the dirt sensor on your vacuum is located in the suction tube and is generally not accessible enough to clean without taking the vacuum apart.

hope this helps,
trin

That can mean the bag is full.

You most likely will need to change the Yoke assembly. There is a sensor built in that gets clogged with fine debris over time. This will take care of the problem.

Your Sensor most likely has an internal heat sensor that is shutting off the motor. Some vacuums install an external heat sensor with a reset button that you must push to re-start the vacuum. If your model does not have an external reset button it is most likely a sensor inside the motor. If it is defective the motor must be replaced to solve the problem. But first make sure the overheating is not being caused by a blockage somewhere or the bag is too full. Air must pass completely through a vacuum starting at the floor where it picks up the dirt through all the canisters, filters, bags, etc. and then is exhausted from the vacuum. Any restrictions or blockage can cause the motor to over heat.
That Vac Guy

make sure there are no clog ups in the hose

Try wiping off the cliff sensors, and cleaning the drive wheels. Download the user guide, if you don't already have one.

There is an optical sensor inside the port where you attach your vacuum bag. Take the bag off and take a clean soft cloth and wipe inside the port to remove dirt from the sensor. Don't wet it! Do this every time you change your bag and you shouldn't have a problem.

The Hoover uses a small microphone that is positioned in the plastic housing that the end of the hose fits into, just behind the bag compartment. What happens is that when dirt comes up the hose and hits the 90 degree corner, just before it enters the bag, the microphone picks up the sound and transmits that info to the electonics that controls the lights. Sometimes the microphone will stick and the red light will stay lit. If you take a screwdriver and give the microphone area a sharp tap with the handle of the screwdriver, this will often jar the microphone and it will begin working again. If not, it may need to be replaced. NOTE: this function does not affect the cleaning efficiency of the vacuum. Your vacuum will still work normally whether the dirt sensor is working or not. It is a totally unrelated function to the vacuum itself.

Try cleaning out all the pathways you can get to. Trapped particles can mess up this indicator. Particularly check the extra mesh filter that is under the bag (there's a plastic grid that snaps over it to hold it into place). Clean that out and make sure the bag is securely in place.