Most or all combi boilers have an air input the same as the valve on a car tyre. You get a tyre pump and pump it back up. On my boiler the pressure is meant to be 10 lbs, but if you decide to re-pressurise the water part of the boiler with the filling loop this will make it seem like you have enough air pressure when you don't. So let the water pressure down to o and then start pumping. Keep an eye on the pressure gauge because as you pump up the air in the pressure vessel this will compress the water in the system. I think what you do next is keep letting the water pressure go down and pumping more air until the vessel is at (10lb) with the water pressure at 0. You then repressurise the water and all should be well. You never know........
poff, October 2012
