Condensation problem?

I have a potterton performa 28 with the flue going directly through the wall its fitted on. Recently i have put an extension on this side of my house and the flue now goes on to a drivethrough with a bedroom above. With the recent cold weather the ceiling above the flue has suffered from a lot of condensation. The flue is about 9 inches below the ceiling and about 8 foot above the ground. Would a deflector solve my problem or do i need to add a flue extension with a 90 bend through the new wall and if so which one.