Hi,
Well if the room is heated to 80f and the surface of the uth is 80F are you sure it's actually working? - does it get hotter if you plug it directly into a socket with no regulation? ( don't do this with it attatched to the tank if that's a possibility - and if it isn't I'd probably move the snake out for the hour or so it would take to see a difference).
Although if the snake has just eaten then wait a couple of days so as not to disturb his digestion.
dr del