Hoover Model U6425-920, Series Q 12.0. runs 3-5 minutes, shuts down on thermal reset. motor shaft and brush both turn freely. cannot detect any roughniss at all in shaft turning.

SOURCE: Bissell Proheat 2x Series 8920 - Brush Belt Metal Shaft Sprocket won't turn

Most likely the brush motor is bad and not turning, part #2036757, would sell for around $23. To get to it, start taking out screws on the top cover, that motor is under the that top access cover.

SOURCE: Hoover WindTunnel Canister: Roller brush motor not turning

These motors have a fuse incorporated in the field winding and it sounds like that blew. These motors sometimes overheat at the front bearing and the bearing will melt into the plastic housing. This will cause the fuse to blow. It sounds like that's your problem. You can remove the motor by removing the three screws on the bottom of the powerhead and then check the front bearing for any bubbling or blistering in the plastic housing. The shaft of the motor should turn easily.

SOURCE: brushes not going round

The brushes on my dyson have stopped going round. I have checked it and they move freely by hand. The belt is intact. What could the problem be? The Hoover is about 10 to 12 years old.
My dyson is a dc04

I would advise you to ALWAYS to FIRST UNPLUG YOUR VACUUM before beginning any service procedure.
One of the main problems with vacuums are that the flat belts on the vacuums stretch and should be changed every 4 to 6 months or 3 or 4 times a year – you can tell by taking off the belt or belts on the vacuums and compare them to the old belts on the vacuum the new belts will fix inside of the old belts and you will be able to see the difference on how much they have stretched – if the belt is a geared belt – they stretch as well but should be changed about one a year – the cost is not that expensive and you cleaning will improve almost double – this also applies for the Dyson DC04 and the Hoover vacuum as well – some of the Hoover vacuums have two (2) belts and they both should be changed @ the same time.

SOURCE: I have a Hoover self

http://geeksquad.fixya.com/ThreadView.aspx?prdid=0&thid=632298
Generic problem for all Vacuums
I have a Hoover self
Posted by thjunk2007 on May 29, 2008
I have a Hoover self propelled Windtunnel vacuum( Model U6425-920) that stops in the middle of cleaning. I have changed the flat belt and I'm still experiencing the problem. I usually have to wait an hour or so b/4 it would work again. Any advice?

Hello,
I would advise you to ALWAYS to FIRST UNPLUG YOUR VACUUM before beginning any service procedure. It is possible that you my have a heat sensor, but as far as what you described you need to change both belts, the brushroll belt and the power drive belt as well and @ the same time. The average belt change is every 4 to 6 months on the vacuum. Does it stop completely or is it just the belt problem. Or #2 is the vacuum giving off a burning smell other than the belts and if it does it could be the motor. Other wise , please call the factory or a local Hoover warranty station in your area. So if you need further assistance, please feel free to contact your local vacuum cleaner dealer in your area or in the yellow pages, or contact the factory phone number or website to further assist you with your questions.
http://www.hoover.com Telephone
Contact our Customer Service Department at 1.330.499.9499
Monday through Friday
8 a.m. - 7 p.m. EST
Thanks, Don the Vac Man
Go Ahead. Use Us.

SOURCE: I own a self-propelled Hoover

http://geeksquad.fixya.com/ThreadView.aspx?prdid=0&thid=794479
Generic problem for all Vacuums
I own a self-propelled Hoover
Posted by gohornsgo on July 17, 2008
I own a self-propelled Hoover Wind Tunnel vacuum cleaner (Model U6425-920). I do now have an owner's manual and was wondering how to clean the HEPA filter on this model (*this model uses a vacuum cleaner bag also).
Hello,
I would advise you to ALWAYS to FIRST UNPLUG YOUR VACUUM before beginning any service procedure. The best way to clean the HEPA filter is to take it outside and use a blower over the trash can and blow off the dust and dirt, or use things like an old paint brush and brush it off, or you can vacuum it off with another canister vacuum or shop vac if you have an extra one. For the best filtration is to replace it, there fore the air flow will catch most of the dust and dirt and then you would have to watch how fast it gets dirty and then do the maintenance.
So if you need further assistance, please feel free to contact your local vacuum cleaner dealer in your area or in the yellow pages, or contact the factory phone number or website to further assist you with your questions.
http://www.hoover.com Telephone
Contact our Customer Service Department at 1.330.499.9499
Monday through Friday
8 a.m. - 7 p.m. EST
Thanks, Don the Vac Man
Go Ahead. Use Us.