You will need to take the top off. It is easy: turn the vacuum over and look at the bottom (where you can see the beater bar). There are some deep screw "wells"; these are the screws you need to take out plus the 4 silver looking screws that hold the beater bar plate in place. When you bet those out, there there will be a "notch" at the front, behind the LED light you will have to disengage. Turn the vacuum back over and take the gray top off. You should be able to see the engagement latch that is attached to the handle. This is what opens and allows the flap to shut. It has a spring attached that may have come loose. Good luck.
On page 11 of your manual it talsk about the pre-filter which I think is the one you are talking about, it isn't to come out, so either is pressed in or glued. But if this is less then 1 year old it is under warranty. If it is then take it in and have it repaired, http://www.hoover.com/pdfs/manuals/U9145900.pdf
Either the carbon brushes on the motor need replacing or the thermal cut out is activating. That might be because it is faulty or because there is not enough airflow over the motor.
Overheating motor causing an automatic shutoff. This is most commonly caused by an air passage that is plugged by hair or dirt.
When your Hoover spin scrub is not sucking up water, the most common problem is the clear round cap located on the suction nozzle is not closed. See pic. Also check the rubber cap on the dirty water tank.
The handle pedal is snapped in to the base, where it pivots.
The pedal needs to be pried away fron the base, exposing the pivot pin to release it for removal. On your model, you will likelly have to remove the lower handle from the base (where it pivots) to get room to release and replace the pedal.
The latch at the bottom of your vacuum cleaner. The problem is that 'React' seems to be a range of cleaners.
Google
make model (number) parts diagram
https://www.google.com/search?q=Hoover+React
..
If your Hoover SteamVac F5851 is simultaneously dispensing the cleaning solution and extracting it while you have the trigger depressed, there may be an issue with the unit's internal mechanism. Here are a few troubleshooting steps you can try:
1. Check the trigger mechanism: Make sure the trigger is not stuck or jammed in the depressed position. Gently press and release the trigger a few times to ensure it moves freely.
2. Inspect the solution dispenser: Examine the solution dispenser to see if there are any clogs or blockages that might be causing the simultaneous dispensing and extraction. Clean the dispenser thoroughly, removing any debris or obstructions.
3. Verify the solution flow setting: Ensure that the solution flow setting on the SteamVac is correctly adjusted. There should be a control or dial that allows you to adjust the amount of solution being dispensed. Make sure it is set to the desired level and not malfunctioning.
4. Check the suction nozzles: Inspect the suction nozzles and brushes to ensure they are securely attached and not damaged. If any parts appear loose or worn out, you may need to replace them.
5. Clean the unit: Give your SteamVac a thorough cleaning, both inside and out. Remove the recovery tank, rinse it, and make sure it is properly reattached. Clean the brushes and nozzles to remove any built-up dirt or debris that could be affecting the unit's performance.
If these steps don't resolve the issue, it's possible that there may be a more significant problem with the internal components of your SteamVac. In that case, you may need to contact Hoover customer support or take the unit to a professional repair service for further assistance.
Question edited for a lot more clarity.
Parts Schematics and Parts Suppliers. Some parts are obsolete, so you might just have to tell your son to find the parts he removed.
https://www.google.com/search?q=Hoover+F5881-900+parts
Look inside the wire crimps with the white and yellow wires for wire strands alongside the other wires (broken off of the power cord). If you see some, that's the neutral connection.
If you don't see any stray strands in either connector, you'll have to trace the wiring. First, check how many connections there are on the power switch. If there are only two (one should be connected to the black wire going to the power cord), the answer is not there, and you'll have to identify the wire that goes directly to the motor and the lamp socket (including any wires connected together).
If there are four terminals on the power switch, with black wires going to one pair of terminals and white or yellow wires going to the other pair, identify which black wire goes to the power cord connection. The white wire next to it goes to the connection you want.
How did you manage to pull the power cord out of the connectors? There's supposed to be some kind of clamp, knot, or other restraining means where the power cord goes into the vacuum cleaner to prevent this potentially dangerous situation. If that is broken or missing, get it repaired before using the vacuum cleaner.