Hi, the pressure of my Vailiant 831 combi boiler keeps rising when I turn it on. I am having to blead the radiator after every 2-3 hours of boiler being on to reduce the boiler pressure or the pressure bar goes to red. It seems like air builds up in the system when I blead the radiator the water has a lot of air bubbles, even when I use the hot water there is a lot of air bubbles. Hope someone can help, thanks[/b]