DNS Issues BT Home Hub

My BTHomehub works until any changes are made to the wireless key password, after about 30 minutes the DNS no longer works

All sites work with IPs but not hostnames, explaining this to BT has been a waste of time though.

If i manually set a static DNS on a client machine such as 8.8.8.8, i can connect fine.

But the DNS of the router no longer works.

If i ping the BT DNS servers this times out even when internet is working.

BT seem to think resetting the router is fine, and that all is resolved, and then it happens again whenever changes are made.

Funilly enough though, they wanted to remote in and were stumped that even after a reset.
Pinging bt.com for example does not work but other sites do.

Tried running a tracert and it just gives up after 10 hops

I cant understand at all whats happening with this.

I borrowed a router from a friend and have had no issues.

Now he needs it back and first day i plug home hub in this happens again.

Anyone got any ideas?

Or can anyone tell me how a wirless key change could affect DNS?

Im asking for a replacement tommorow, and will see how it goes with that.