Refresh the key
On House, choose the channel and ask for a new stream key. Confirm it. The previous key no longer works.
The encoder
Paste the new key into the encoder before you go live. A key that is still the old one will not bring the picture up.
Do not delete the channel
Deleting the channel is for a channel you no longer use. A leftover key is fixed by a new stream key on the same channel.