Originally Posted by
cornerstonehvac
First off, you cannot bleed the boiler from the bottom drain. In order to bleed the system you need to do 1 of 2 things depending on the system . I'll try to explain what to look for and how to bleed the system so bear with me. You also mentioned that there was a pear shaped valve on top, that most likely is a Hy-vent. If the hy vent is not working it should be replaced before filling the boiler. You may be able to get one at lowes or Home depot I'm not sure or you may have to get it at a hvac contractors shop,but I would recommend that it be replaced.
1)- On the return piping(usually the piping that the circulator is on) there may be a purge set up. It consists of a shut off valve with a drain valve above it. If your system has this, this is the way to bleed it.
Start by turning off the system. then make sure you have approx 12-20 lbs of pressure on the boiler. Close the shut off valve and hook a hose up to the drain above the valve. Open the drain and let the water start flowing. You will get alot of air then water then air and water, keep an eye on your pressure guage, if the presssure falls below 10lbs kink the hose shut to allow the pressure to build back up in the system( becarefull not to go passed 30lbs. or the relief valve will release). Let the system bleed until you are getting nothing but water. Shut the drain valve(where your hose is attached) and open up the shut off valve below it. This may need to be done a coupe of times to ensure all air is out.
2)- If you don't have a purge set up as decribed above then there are bleeders on one end of each of the Radiators or baseboard. You will either need a flat tip screwdriver or a bleed key and a rag and small can or cup.( bleed keys can be purchased at either Home Depot or lowes). Make sure you have at least 12 lbs of pressure on the boiler guage then go to the baseboard/radiator closest to the boiler and open up the bleeder about1/2 a turn you will get air ,water and a mix out. Once you get nothing but water , close it down and then go to the next one and repeat. Do this until you have bled out all baseboard/radiators. Check the boiler pressure guage occasionally to make sure there is enough pressure for bleeding. This may have to be done a few times to ensure that all air is out.