We never had a problem before the new boiler but now air keeps gathering and practically every week it is noticeable that the upstairs radiators become cold at the top, I then bleed the upstairs radiators - loads of air to let out - I do all that with all the upstairs rads till all of them have no more air (till very small amount of water spurts out) and then all of them are hot at the top of every rad. A week later and back to the start - air has gathered at the top inch or so of all the upstairs rads and I have to do the same again. We never had this problem with the previous boiler - a combi - but now we have this new boiler - a condensing combi - since it was recently installed we've had pressure problems and air gathering that needs to be let out. That's been the only change - the boiler. Anybody know what could be the problem? Any advice would be appreciated. Thanks.