a HVAC professional that I know measured the temperature drop on the return on the hot water circulator boiler system in my house (older, home was built in late 50's). He said the drop was not enough, indicating sediment/ and or air bubbles in the system. My problem is, he does not service residential boiler, and just check a couple of things to help me out. No one in my area does residential boilers anymore; how can I flush this sytem completely myself? I'm guessing that once I get it back clean again, I can keep it there by learning how to do the blowdown regularly.
You could try draining your system and refilling it. Shut off the water supply to the boiler, go open all the bleed screws on your radiators. Then find the drain on your boiler and let it empty. It will probably take a while. After its empty, close the drain and bleed screws and turn the water back on. Now you'll have to go bleed all of the air out of the system. Start on the 2nd floor with the radiator farthest away from the boiler and work backwards. You'll probably have to bleed the radiators several times before all of the air is out. If you can get the circulation pump to kick on while you're doing it, it may go a little faster.