I have a Vax v7 that is 4 years old. I have replaced the filter and ensured no blockages are in place. The dust collector has been emptied and cleaned and yet after a few minutes use the suction ‘oscillates’ and cuts out. I have tried running the Vax with the attachments connected directly to the device (no pipe) and it seems to be OK but I haven’t tried this beyond 5 minutes. Is there any other possible cause for this issue?