The small belt attached to the roll brush keeps slipping off. It's a brand new belt and the vacuum is only 1 yr old.

The Brush is pressed into a small holder on each side of the vacuum case. You must pull the brush forward (out) from the holders and on the brushes side is a spindle where the rubber belt wraps around. Remove the old belt, clean off all debris and put the one end of the new belt on the spindle end of the vacuum motor and the other on the brush end. Push brush roller back in place and you are good to go.

Either your belt has stretched beyond its specs or you have larger problems. Are you talking about a new belt? If not, try a new belt. If so, check to make sure the beater bar will spin freely without a belt attached. If it spins without a belt attached, make sure the bearing blocks at both ends are in good shape.

Your belt has most likely burned in half, this happens from an object getting caught in the brush roll, a brush roll that does not shin freely i.e. debris under the end caps or usually and old stretched out belt that has been slipping; belts can stretch out in 6 months whether you use the vacuum or not.
Remove the brush roll and old belt, inspect for damage, clean out the area and instal an new belt or the same brand and type. It should be good as new.

Those machines have the belts on them at production.
You can read about this
www.vacuummedic.com/blog/2012/10/09/my-brand-new-vacuum-doesnt-work/

Change the belt! Good as New!

Good Luck
The Vac Dr.

Be sure to unplug your vacuum from the electrical outlet before proceeding!

-Turn your vacuum upside down so that the handle is resting on the floor and nozzle portion is resting on a work bench.
-Remove the 2 phillips screws from the metal bottom plate and set the bottom plate aside.
-Look at the right side of the brush roll. You will see a bent metal rod that attaches to the brush roll end cap. This is the clutch rod that allows your brush roll to spin or not depending on the position of the carpet/floor switch on the top of the nozzle. Pull this rod out of the brush roll clutch only. Leave the switch end of the rod where it is and just let the rod rest there.
-Pull the brush roll and old belt out and dispose of the old belt.
To install a new belt; put the new belt on the motor shaft first, next put the other end of the belt over the end of the brush roll and stretch belt and brush roll back in to place. Notice that on the brush roll end cap opposite of where the clutch rod goes, there is a metal piece with a slot cut into it. Be sure that this slot mates with the plastic stop in the nozzle so that the end cap cannot move.
Snap the clutch rod back in place and rotate the brush roll by hand to make sure the belt is not pinched.
Replace the bottom plate.

Remove the glide plate at the bottom of rhe machine. Remove brush and broken belt. Fit new belt and re install brush. Fit glide plate, job done.
Its in the instruction book

You could try contacting Hoover for parts availability. If it's and older WindTunnel and Hoover no longer has the part, try eBay.

There should be a belt tensioner for the V belt, maybe it is not contacting the belt when you tilt the handle back. If this is less then 1 year old, then it is under warranty, take it in to a warranty servicer for warranty repair.

You may have a bad brush roll, part #61250-1, or the base itself has a problem and isn't letting the brush roll sit straight so it can be in alignment.

remove bottom plate, remove brush roll. slip new belt over motor shaft then onto brush roll. refit brush roll and bottom plate. its just meccano