Try increasing system pressure to between 1 and 1.5 bar. To fill the system with water you connect up the flling loop, if it is not already connected. Look under your boiler it is usually a flexible silver braided type ruber tube but can sometimes be solid copper with a lever (black) this will be connected between the cold water mains inlet and the Central Heating pipework. When you turn this lever you will hear water running and the pressure gauge should begin rise, wait till the pressure is 1 to 1.5 Bar. You should then turn off the tap and remove the filling loop to comply with water regulations. (Removing it also means if the tap leaks the pressure won't go up) The down side is if it was already connected there could be system pressured water in the filling loop so do it carefully and be ready with a towel.
Peter, November 2009
