preferred wifi network won't stay connected

Hi,

I have a 2010 macbook and since updating to Yosemite 10.10.2 the connection to my wifi won't stay connected - tends to last only 3/4 minutes before I have to manually reselect the network. It immediately reconnects without me having to retype the wifi password and the network is the only one in my preferred networks. There were no problems previously and the signal is consistent when other people connect laptops and iPads and I have my iPhone connected to it.

I have had a look at the standard apple troubleshooting guide for network issues but it's pretty useless as it seems to assume that the problem is with the router or with the network provider.

Any advice would be greatly appreciated,

cheers

Ollie