We have an oil burner about 3 years old and a large hot water storage tank that works off the boiler and also provides hot water for household use. The "zone" that serves the basement is not working. When we turn up the thermostat in the basement, we get a "whump, whump" noise. Kind of sounds like the washer when it is spinning but the load is a little unbalanced. There is little or no heat getting through. Could there be air in the line? Any idea how to troubleshoot this problem? Also, since these pipes wind all around the basement, could there be a section that has frozen? We bought the house after the furnace was installed, so we don't know much about this type of system. Heat to the other zones is working great.