Wireless Router Keeps getting Disconnected every 4 Hours

My Belkin F5D7230-4 v6000 wireless modem disconnects every 4 hours. It has the latest firmware version(F5D7230-4_US_8.01.21), acquired from Belkin website. I have DHCP on and a "forever" lease time. Security is WPA/WPA2-Personal(PSK) with TKIP + AES encryption. Resetting it to factory defaults doesn't do a thing. I already called my ISP and confirmed that I have correct settings. Anybody knows what could be the problem?
