Hi Margaret,
Dyson is a good machine...what better can you buy!
As for your question, there is either a blockage or a leakge.
At the bottom of the vertical pipe (near floor) is a flipper which should stay closed unless something is stuck in it..usually a metal object that has been sucked up.
Next check if there is a vacuum at the top hole with the dust unit removed. Thisis quite a powerful suction. Between the motor and this inlet should be all clear..so check for obstructions.
The motor can be checked by checking suction on the dirt filter side. The filter enclosure should also be properly closed as it will leak and lose suction. Hope this helps. Raj
Raj
June 2011