: I have tryed to bleed the zones where I hear the air/water mixture? Do I have the system on , with the aquastats open ? I think I have tryed this every way possible , I have 4 heat zones oil burner . ThanksAir in the lines is a common problem. Depending on the system design it will effect the ease of bleeding the lines. It is best to run the zone open so the water cycles and the air is carried to the high points (where you should have bleeder valves). If you cant get it this way, I have had to connect a water hose at the boiler and try to force water through the system. This requires opening another drain so the water can run all the way throught the pipe system. You should also have an automatic air scoop installed at the boiler which will catch the air as it cycles through the system. If the system is not designed to make it easy to releave the air, I suggest you change the design to make is easy.