Bled two of my rads last week, ever since the pressure gauge keeps falling to the left (low pressure). I've got a Baxi 133 HE Condensing Combi, the gauge is marked in three parts: 0-1 (Red, low pressure, possible leak), 1-2.5 (Green, normal pressure, OK), 2.5-3.0+ (Red, high pressure, problem)...