During the summer, I had 2 radiators replaced with new ones and another one removed and capped off as it was no longer required. The work was done by local plumbers. Now I have tried the heating system, all the radiators stay cold. When I turn up the thermostat, turn on the heading, I hear the pump start and the valve open as the pipe to and from the valve gets hot. But that is it. The hot water does not seam to go to the radiators. I have bled all the radiators. The hot water system works fine. Any ideas?