Hoover Mach 5 sweeper
Had this same problem with my Mach 6 (same as Mach 5)
It would shut off after 15 min of use. What is happening is the secondary filters, HEPA and the canister all need to be cleaned. This is vital. What the vacuum repair people are keeping from you is that tidbit of wisdom. This particular vacuum is picky about airflow. Pull the canister, and on the body of the vacuum on top of where the canister sits are the secondary filters. There should be a sticker explaining how to remove them. Clean them throuougly, mine was filthy. Make sure you clean the canister by unlocking it and cleaning out the micro holes and the cone end. Mine was completely plugged. Now brush the dirty side of the HEPA filter with the combo tool. Let the secondary filters dry completely (you can blow dry them on cold) Re-install everything, and the vacuum will run like brand new. I vacuumed the whole house after I completed this maintainence and it works like a champ. Don't return this vac until you clean it completely.