My Hoover WindTunnel upright has little suction in accessory hose?

Recently our Hoover WindTunnel bagless upright has been almost useless when using the handheld accessories like the furniture brush, etc. Almost no vacuum in the hose for the handheld tools.

All the filters are clean, there is no blockage in the hose, the canister is empty. What seems to be happening is that when the cleaner is locked in the upright position, it still pulls strongly from beneath, instead of through the hose. Isn't there something that's supposed to seal off the bottom vacuum line when the machine is locked upright? Thanks for any help!!