New windtunnel bag vacuum worked fine for about a week but now is unbelieveably hard to push at same setting on same carpet as before.

Belts get hot when fibers from carpet get wound arounf the belts mounting shaft. Best to take a razor and cut off any fibers so the belt doesn't get hot again

This is a typical problem you are describing. I would recommend you change the belts, this will resolve the "hard to push" and most likely resove your issues. based on the s/n given you maching was made on sept 2004.

I’m happy to assist further over the phone at https://www.6ya.com/expert/robert_b96ba3f038cf317c

your floor adjustment spring is broken there is a plastic slider and clip if it is broken the height adj will not work you should get a new vacuum because this repair can cost as much as a new vac.also this is a common problem with the hoover brand I would get a sebo or an oreck they have a great warrentty and you will more than likly never buy a other vac.

Make sure the vacuum is on the carpet setting..the brush won't turn on the hard floor setting..

The suction is so great that it sucks up your carpet, then nothing works. I get my children to stand on the corners/edges of the rug so that it stays perfectly flat on the floor while I vacuum. Or, you can turn off the brush roller (set it to "hard floor" setting). Or, tip the vacuum cleaner's front up slightly while vacuuming, to reduce suction.

these dark marks are burn marks from the beater bar itself. most walmart, kmart, and target shelf vacuums from hoover, dyson, and any cheeper vacuum has a hard bristle system. I've noticed even on the high end hoovers as well that they do the same thing. the best way to save your carpets is to see if there is a replacement beater bar that can be substituted for your vacuum. i dont know what style of beater bar that particular one is but check with your local vacuum repair center to see if they have something with softer brushes you can use insted otherwise i would recommend a new vacuum with softer bristles. usually something that is half as stiff as what is already on yur unit. you culd also try lifting the hight setting as a temporary solution.

When you had the brush roll off, did the ends turn freely? If not then the brush won't turn and the belt will just slip. You would have to replace the brush roll if either of the ends are frozen. Other then that you would have to remove the top cover to see if there any broken parts, there is a spring loaded asm, it has a black wheel that will push the V belt when it is in the carpet setting and the handle is in the down position, it could be jammed so the roller is stuck.

· Sometimes grabs the carpet for no reason.
· Comes back too fast when I push it back.

I would advise you to ALWAYS to FIRST UNPLUG YOUR VACUUM before beginning any service procedure.
Self-Propelled WindTunnel by Hoover U6445906 Without knowing the brand name or model number you may have the height adjustment to low and the vacuum will say “bite down” on the carpet of which will make the belt burn and might leave marks on the carpet – and if you have a self-propelled vacuum it does come back fast if you because you have a transmission just like a car and you have to control the speed of the vacuum or because it may have a weak belt the vacuum will pull back easier – I really would like to know the brand name and model number so that I could accurately give a better answer . Recommended belt change for flat belt(s) are 4 to 6 months for better cleaning and one a year for a geared belt – both can stretch and lose their cleaning function

could be, but probably just needs a new belt - they stretch.