In article , says...
I have a Dyson DC03 vacuum cleaner with a broken drive belt. It is the
belt between motor and clutch, not the one from clutch to brush
cylinder. It looks as if bits of string have stopped the brush from
turning, the belt has stalled and burned through.

The original belt is 25cm long, shows no sign of damage or real wear
apart from the burning at one point and is part number 004300-01.

A supplier (ukvacuumspares) claims that 002514-01 is the right part but
that is only 20cm long. It was a struggle to fit, it snapped
immediately the motor was turned on and on dismantling again I found the
casing had been overstressed and cracked.

Now Dyson support are quoting 902514-01 but that may just be a typing error.

Has anyone replaced successfully or had these problems?

My DC03 burned out its primary belt and it was fixed under warranty.
They also replaced the clutch to stop it happening again. Apparently
this was a known problem, I guess they had a batch of faulty clutches
which didn't slip at a sufficiently low torque - maybe you have one of
these, in which case a new clutch would seem to be a good idea. I
wonder if they changed the clutch diameter at some point.