Hi I had to disconnect two radiators whilst decorating and lost pressure in CH system. After replacing rads and repressurising system the pressure gradually increases when CH system off. If i leave filling loop in boiler position pressure gradually increases, if filling loop is in off position there is no pressure increase ( but no HW obviously) I believe it is the heat exchanger would I be right? poss pinholed due to the difference in pressure when drop in CH system???