sailor

liberty

What is the best way to bleed air out of a hydronic heating system, that has no bleeders.  The system is one floor, seven radiators, boiler in the basement. The boiler heats up and operates correctly, but the radiators are not getting the hot water, and it seems like the system is air bound.  Thanks for the help. 

Jean-David Beyer

Bleeding system.

First, be sure that being air bound is the problem. If your circulator is defective, for example, bleeding would not help. Similarly, if you have a Y-strainer that is clogged, that should be cleaned. When the system is off, is the water pressure correct (usually 12-15 psi)?



If this system was working last year, I would wonder how it got air-bound. Leaks? Then you better get them fixed. In my old system, I had key-operated vents upstairs, and I always got water out, not air, and I had that system from 1976 to 2009.



If the system were not air bound, in my opinion the best way to bleed it would be with a fancy air separator, such as Spirovent or Taco 4900 series. These can remove air that is dissolved in the water. So small amounts of air can dissolve in the water and be removed by the air separator. This works for me because I have base board upstairs with no vents at all. But it takes a while.



But once the system has so much air in it that water does not circulate, that will not work.  If your system has purge valves, you can purge the system. Best to do this with the heat off. Hook up a hose to the purge valve and run the other end to a suitable place (e.g., drain). I use my driveway. (I would not do this if I had anti-freeze in there. D.E.P. might get mad at me.) Then close off the isolation valves so that the makeup water will go through the heating zones (and not the boiler). Then open the purge valve and turn the make up water on full. Watch the end of the hose until the air bubbles stop coming out. Then let the make up water go back to normal pressure and turn off the purge valve. (If you turn off the purge valve first, the pressure relief valve may go off.) Open the isolation valves before starting the system again.



You might wish to get a professional to put in some air vents, either the ones you open with a key, or the automatic ones. Similarly, if you do not have purge valves, you might get a heating professional to install them. I recommend a heating professional instead of an ordinary plumber, because while the ordinary plumber can certainly put a valve anywhere you ask him to, he might not know just where to put it, and might not know to put isolation valves in or where. Some plumbers undoubtedly do know these things, but I would not depend on it.

Mark Eatherton

Got pictures????

I have seen older systems that had no vents on the radiators for a reason. The trapped air in the radiators is considered the expansion absorption function. Bleed the air out and you will be replacing the pressure relief valve. Numerous times...



Unless your radiators are supplied into the bottom and the water then is piped out of the tops, you can not power purge it as JD has explained. You can't maintain enough velocity to power purge radiators that are bottom tapped for the supply and return.



Sometimes, it requires having to increase the operating pressure to compress the bubble further up into the radiators. The radiators were originally oversized vertically to allow for this. For example, if the loss calcs determined that you needed 2 foot tall radiators to do the job, then the contractor installed 4 foot radiators, and the upper 2 foot became air storage to handle the expanding fluids.



But this is just one potential. Need to see some pictures of your near boiler piping and the radiators to see for sure.



ME

Steamhead

No bleeders?

If it really is hot-water, it would have to be one with an overhead main. In this case there would be a main air vent at the top, or perhaps the expansion tank is connected there and handles this.



If not, it might be a Vapor system.



Post some pics of the boiler and radiators and let's take a closer look.