Hi, first post so excuse me if i don't make sense, Combi is a Vaillant GB 242 EW, has a drip coming from somewhere in the boiler, approx 1/4 to 1/2 mug of water, only when cold, ie overnight at this time of year, pressure is fine during the day when boiler is on and no sign of a drip anywhere, when boiler is off pressure is down from 1.2 bar to 0.5 bar, the thing is refilling via the filling loop takes literally a turn on of the valve for a second or two and the pressure is back to 1.2, turning a tap on for the same length of time wouldn't fill a mug with water. My question is this small drip the cause of the pressure drop?