I've had no book symbol up for a month or two now after changing the pot on the rhs blend. Last two mornings have flagged the book up after the self test and it defaults to screen only which makes sense from a safety point I guess, I cannot change air direction.
However, after the brief journey to work and starting her up again a few hours later when coming home....no book symbol and everything is well again.
Why would a fault exist first start every morning but not on the 2nd ,3rd,4th etc of that day? Ambient temp is fairly constant so heater box 'tightness' being my first thought, seems unlikely.