is this without using the motorized head ? if not then try without.
If you have a fault on the main hand unit then these are generally unserviceable i find.
Only other things i can suggest are cleaning the battery connections inside the main hand unit after removing the battery.
These do become dirty and can become slightly high resistance.
A cotton bud and isopropyl will clean them, servisol switch cleaner would do as would wd40 as a last resort.
Ensure the non return flap isn't siezed half way closed, just behind where the tools connect to body.
Every one i have seen is jammed fully open allowing the crap to fall out of the bin when unit is placed back on the wall mounted cradle. However they can jam half way restricting air flow. but generally the machine will hunt if it thinks it's blocked.
other than that you will have to bin it.
I did see someone on ebay recently selling a brand new motor assembly for a v6, which i thought was strange as i as previously mentioned they were unserviceable