We have an older home [70 years] with steam heat. We installed a new gas burner/boiler to replace the oil burner/boiler. Since the change we have had problems with balanced heating. Some radiators heat and others do not. Our heating service person is young, intelligent, and has been very attentive with the problem. In our area of the country [Tennessee], steam heat is a rarity, particularly in homes, so there are no "experts" around. We have been able to pretty well target the problem as air locks. We have two types of radiator: standing iron radiators with an inlet pipe [top right] and outlet pipe [bottom left]and recessed radiators with thin metal sheets and inlet/outlet pipes at the same level. Currently our problem is with the standing radiators. The standing radiators have a control knob on the right [top], where counterclockwise is open, and a small flat control valve with a hard rubber center on the left [bottom]. The latter has no visible air/steam release. When one of the problem radiators was bled by releasing the nut between the control knob and the radiator [top], it worked fine for a while and then stopped heating again. In the basement there are three steam/air valves, two large and one small. There are not, as best as we have been able to determine, no such valves at higher levels in the house. On the Internet earlier I found on the Gorton Heating Corporation site a valve system that sounds like it might be what we are looking for. However, they have not responded to E-mails or telephone calls. Apologies for the laborious detail, but we need help! many thanks.