Default wifi and mobile data not autoswitching

hi guys - ive got a samsung galaxy note 3 here in the uk, its about 4 months old, on tesco mobile, it doesnt seem to switch between mobile data and wifi...if im at home and connected to wifi then i go out, it switches to 4g, but when i get home it should switch back to mobile data but it doesnt, both wifi and mobile data are on and ive placed a tick in the" auto network switch"...but it doesnt switch over...any ideas ta?