Vodafone thought it was a router problem so have sent another one but it does the exact same thing.
The problem is that DNS seems to stop working in the router.
All devices on the network (desktop, 2 laptops, tablet and iphone) are set to DHCP and they all have the same issue.
The internet seems to work fine for a random amount of time, this has varied from a few minutes to a day, then suddenly stops working.
You can still ping, and access websites by, IP addresses when this happens.
The router status says it is still connected, which it is, and to get the desktop working I manually put in the Vodafone DNS servers and the internet works again on it.
Normally, with DHCP, the DNS servers are set to 192.168.1.1, the IP of the router.
A reboot of the router usually fixes the issue but not always.
What's going on?
It's not a problem setting the DNS manually on the desktop but the other devices are used on other wifi networks so setting the DNS servers manually is not really a good option, besides we shouldn't have to do this.