Our Dyson DC04 isnt picking up anywhere near the strength it used to, I have changed the filter on the top of the dust tank and still no better. Im quite sure there are no blockages anywhere, and when we detach the flexi pipe for doing the stairs etc etc, it sucks really well. The only thing that i can see that isnt right is that all the stuff it does manage to suck up stays at the top of the dust tank, and doesnt fall to the bottom.......Has anyone any ideas on what the problem may be 
