Our boiler has always needed a bit of topping up on a regular basis, but recently it seems to be getting worse - in the morning the pressure can sometimes be so low that it refuses to fire up. However, if I re-pressurise it (just enough to take it out of the red zone), it registers about 2 bar when hot and will happily stay there all day, so if there's a leak why is it only when it's cold? I can't imagine any leaky joint is going to expand with heat and seal itself quickly enough to keep the pressure up.
-- Halmyre