Hi, I have a bit of a puzzler (at least for me). I have fitted new radiators (some double panel and others cast iron ones) and rerouted some piping that went up the middle of the wall. But now one radiator keeps getting air in it. I know why it is just this radiator (there is a rise up from the floor below and then some poorly angled piping, so this radiator comes off a high point - like a bubble trap). But I don't know why the air is there. The system is sealed and hold pressure at 1.8 bar (I was away for 2-3 weeks and it did not drop a bit). I have inhibitor in, and the gas does not burn. But this morning I had to bleed almost the whole radiators worth of air (built up over a few weeks). Any ideas? I am very confused as the air only comes in when running, and I don't have to refill the system by adding new water.