We have moved in to our new home 3 weeks ago. We have turned the heating on but only the upstairs radiators were getting hot. The downstairs radiators were ice cold. If we turn the radiators off upstairs than downstairs is getting warm, but if we turn the upstairs radiators on again then after a few minutes the downstairs radiators getting cold again. We have tried bleeding it first and then draining the system. But no luck. We already had 2 servicemen from 2 different companies here to have a look on our situation, but the only thing they have done was tearing up the floorboards and the second plumber have changed the flow switch. But sitll no heating downstairs. The boiler was replaced 4 years ago so relatively it is new. The plumber said that the pump is working. The property was empty for quite a while before we have moved in 3 weeks ago. At this point we have no idea where to go next. Many thanks.