Detects Wifi Network but ignores it and uses 3G

[zombola]

Hi
Wondered if anyone is having the same problem.
My Iphone 4 has suddenly started ignoring my wifi network.
in Settings>WI-FI my network is highlighted in blue and ticked, yet when I use safari it automatically uses 3G.
I tried turning 3G off and it then just goes to 2G (small circle). My Macbook, Girlfriends Iphone 4 and flatmates Iphone 3 are all connnected to my network and work fine so it is not a router problem. My phone has always worked fine until today.
I haven't changed anything on my phone or network so can't understand whats happened.
Any help appreciated.
Thanks
Ash

 

[zombola]

*Update
Just tried again in Settings>general>Network
turning 3G off and got a wifi signal for about 5 seconds, tried laoding a page in safari and got the error message 'Cannot open page as a network connection is not allowed.'

 

[5er driver]

I had the same issue and found that I had to update my router's settings. I had 5 devices' MAC addresses entered into the router's MAC Address Filter setting but only 4 "maximum connections allowed" in another setting. Everytime a computer booted or iPhone tried to access the Wlan and was not 1 of the previous 4 devices to use it, I had to reset the router to accept it. Make sure the "maximum connections allowed" to the Wlan is correct. If it is set at 3, set it to 4, 5, or 6. That is safe as long as the router uses MAC Address Filtering and you enter only the MAC addresses from the devices that you choose to have access to your Wlan.

 

[ISean]

Make sure you are using your router's encryption password and not the admin password.

 

[LGMarines]

Check your wireless router's channel frequencies. I had a similar issue and that solved my problem.

 

[zombola]

so I've just sat down with my mac and iphone to follow your advice and sort this out and the phones wifi works perfectly, full signal ...and I haven't done a damn thing!
Thanks for your help anyway.