iPhone 4S can't find any WIFI networks

I have a 2yr old iphone 4s and the WIFI for the past week won't find any networks. Wifi turns on ok but won't pick any networks up. Have tried at home and at another persons home (both previously worked ok). My iphone 5 and ipad picks up both of these wifi networks ok.

I've tried resetting network settings and have also factory reset the phone but still no luck. Is this a hardware issue (bluetooth works fine and connects), or is it a iOS problem (currently on 6.1.3 and was working fine on this since it was released)?

Thanks for any help

 

Thanks, thought it was probably a hardware issue. Is that a repairable item at repiar stores? Its not under warranty and not sure I'd want to pay too much as will look to upgrade to the new iphone later this year. How much is an out of warranty replacement?