Common generic problem with Dyson upright vacuum brush bar

Remove brush bar cover...is the belt broken, cut or stretched to the point of being ineffective? Is the brush bar full of hair or string?
Pull the belt forward...does the pulley spin? Turn the cleaner on
and see if the pulley spins...if it does I think a new belt will be needed.
Be sure to buy the right one.

Regards,
Dennis


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Most likely a broken belt.

Not familiar with the DC18 but some models have two belts - one connects the motor to the clutch (if when working normally, the brush stopped rotating when the cleaner was in upright postion then it has a clutch), the other connects the clutch to the brush bar.
One is easy to check, but the other is under a plastic cover and needs a Torx driver to remove. Both belts are not easy to replace.

Hi If your Dyson has a brush protection design - i.e. roller bar on the top of the hood on the left hand side then the DYson can't be repaired by you- serviceman or professional care can replace it.
However if the Dyson doesn't have the roller bar on top of the hood, flip the machine over so that the beater brush is facing upwards, locate three/four screw heads that can be undone with a coin and remove the sole plate assembly. This should give you a clean view of the brush bar, drive belt and dirt channel. Ensure everything is clean espcially if the brush bar has lots of hair or threads tightly corded around. Then locate the drive belt and check to see if it has snapped. Grasp the beater bar gently upwards and the belt and brush can then be removed. Fit a new belt on carefully and check the tension as it will be tight.

If the Dyson model has a brush bar control roller at the left hand side of the top hood then it won't be able to be repaired unless its by a Dyson call out or someone who repairs Dyson models with brush control protection.
If the model doesn't have a brush control dial then you will have to change the drive belt:
Easy to do if you flip the machine over with the beater bar looking upwards. Locate the three/two screw heads and undo with a coin. When the roller section is revealed by taking off the floor head you should replace the belt with a new one and be careful putting the beater bar in the right way on both ends. The belt will be tight brand new so expect some tension in it.
If this works for you please rate Fixya! Thanks.