Re-pressure boiler every morning?

I have a Vokera Compact HE Boiler? I am having to re-pressurise it every morning? there does not appear to be a leak anywhere? but I have noticed a drip from the boilers overflow? Is the pressure leaking off here? overnight? Is it a known problem with this type of boiler?Red light on control panel every morning, top it up reset and its ok until the morning when red light comes on again?