Why does green/red clean sensor light start green, then turn red and stay red?

SOURCE: Embeded Dirt Finder

check out the switch that activates it. go to thehooverstore for a complete listing of hoover machines. I'm sure you'll find your machine listed along with an exploded diagram of the machine

SOURCE: Electrolux Epic 6500SR Full Bag sensor working, Does not Reset properly

The problem was a sticking switch that was not being reset. The vacuum on/off switch mechanism is comprised of two switches. One is the main switch that turns the vacuum on and off. The second is a shut off switch that gets tripped when the full bag sensor is engaged. This second switch is supposed to get reset when you push the on/off switch on the outside of the machine. The full bag shutoff switch was stiff and it, therefore, was taking a couple of presses of the on/off switch to move the shutoff switch back into the running position.

SOURCE: Power cut off after handle was dropped on floor while vacuuming

connections inside the handle came loose. happens to me all the time. take the handle apart and connect the wires back.

SOURCE: hoover windtunnel dirt finder light stays red

I'm not sure about a 3 month old vac, I'd probably go the warranty route. However, for the older vacs thy start getting false positives. The sensor is simply a microphone hooked to a computer chip detecting sounds of dirt entering the bag.
To rig it to start working, you'll need to remove the tool accessory tray and elbow that enters the back of the vac, and attached to the bag. This will reveal the microphone at the elbow, and wire that runs into the bottom area of the vac. When on, a large amount of air comes from the bottom screw and area where the wires enter. My fix was to clean up the microphone contact points a little bit with a screwdriver, and then leave the vac running while putting in dampering in the hole at the bottom, and around the back of the elbow. Cotton balls and electrical tape at the bottom hole, and napkins around the outside of the elbow (wedged between the back of the vac assembly and elbow did the trick). The schematic for the vac is here: http<colon>//www<dot>vacsrus<dot>com/CartGenie/pg_U6485900<dot>asp
Look for micrphone.

SOURCE: I have a Dyson vacuum. The vacuum won't stay

My vacuum had this exact same problem, but was out of warranty because it was remanufactured. Thankfully, it's a very quick, five-minute fix.

1. UNPLUG The Vacuum!
   
2. Remove the cannister.
   
3. Extend the handle and remove it.
4. Remove the two torx (T-15) screws behind the power button, where the handle normally stows.
5. There are four tabs holding the front plate containing the power button on; use your screwdriver to release them.
6. Gently pull the front plate off.
7. The switch on the right is the power button. Remove it, try clicking it a few times; if it sticks, great! Replace it and reassemble, otherwise you'll need to replace it.