I just got myself a second hand DC28c cylinder ball vacuum. Apparently this identical to the DC39 if anyone has that.
The issue occurs when a blockage over the nozzle occurs, such as putting the simple circular end flat against a surface. There is then a auditable 'pop' and a change in tone of the vacuum which then remains even after the sucking nozzle is free in open air.
I tested by using a rotary brush (watching the rotors spin under physical pressure) and the suction seems to be reduced somewhat. The only way to rectify the problem is to turn the machine off and on again after a couple of seconds. When the machine is turned off, you can hear a similar but different 'pop' noise again as it spools down. I would describe the noise as a blockage being released and the sound of easier air flow.
I have striped the machine down to the post motor filter and cleaned as I went and can see no obvious issues.
I tested the vacuum with no pre motor filter or cylinder with only the direct opening that pulls air from the cylinder by again putting my fingers across it slowly (incredible suction here) and the problem occurs when a certain amount of the inlet is covered, again not being resolved until the machine is switched off and then on.
This is an issue as it reduces suction and reduces the ability of the turbo brush from spinning, the issue occasionally occurs when using this and the other floor tools.
After vigorous searching online, I believe the issue could be a relief valve / bleed valve issue. I cannot find information on this model. Does anyone know if it has one and how to access it?
No burning smells by the way.
TLDR: my dyson makes a popping sound like it's getting blockage after a certain amount of the nozzle is covered up, reducing suction. This is only fixed by turning it off and on again. Please help, could be a relief valve.