Code 04 means the presure is below 0.4 bar. Under the boiler, there will be a tap at the end of a braided pipe. open this slowly until the presure is up to about 1.5 (green band) on the gauge (This will rise when the heating is on). If the pressure drops over a few days, you have a leak in the radiator system somewhere. The boiler probably wont spark as a safety feature until the pressure is sufficiant.
Jamie S, February 2007
