with my on going problems with this boiler it has now decided not to allow me to top up the pressure. It is with nothing working at .8 bar and 1 bar when heating on. I attempted to top up to 1.5 but there is nothing happening when I open the cocks. so far I have checked that the cold water in let tap is clear. If I close the water inlet tap and open the Water Service Flow Tap, water will run back out of the bleed screw in the pipe. Above that I am in the land of don't know. Any ideas.