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Slow heating on half of system

andyz Member Posts: 18
2 pipe gravity fed system. Two mains from boiler, new Gorton #1 at end of each main,

both mains same heat, wet returns same heat. both mains drop into a common return loop, no apparent blockage here as one side works fine. Boiler 2psi max


Dry return on one side cold (and ALL radiators partially warm). Other main (and radiators) fully hot.

Question, obvious air is not getting out, so wheres the blockage, hold up? I can see the Gorton breathing.

There is also a main vent at the dry return above the boiler, that whistles merrily away, but that is common to both dry returns.


    STEAM DOCTOR Member Posts: 1,943

    if the cooler main is longer or bigger then the hot main then you should try to increase the venting on the cool main. if you post the dimensions of the two mains then the experts can advice you on proper venting venting. do the two dry returns connect above or below the water line ?
  • andyz
    andyz Member Posts: 18
    Pipe dimensions

    The hot (working leg) is 83ft x 2.5 o/d (2" for last 10 feet) the non working side is 73ft x 2.5" od.

    The working leg originally had a Dole Model 90 vent, the other a Dole Quick vent float air valve #5. Both were replaced with the Hoffman #1.

    Interestingly before the Dole#90 went down it was always the "breather" now it is silent and the air valve on the other leg is making all the noise???

    The dry return connect above the water line.

    Thanks for any help
    STEAM DOCTOR Member Posts: 1,943

    you definitely would benefit from a lot more venting. you probably need 4 or 5 times what you have now(i don't have the numbers in front of me right now) there is an ebook that you can buy on this site for $10 that deals with different venting capacities of different air vents. how large is the hole that the current vent are screwed into? 
  • andyz
    andyz Member Posts: 18

    I made a mistake, the new are vents are Gortons, (#1) but I think they are equivalent to the Dole and Hoffman. They are 3/4" Air Eliminator Main Vent Valves.

    I agree venting would seem to be an issue, but odd that nearly identical main legs operate differently. That's the puzzle... and affects all the radiators off that main, so lockage is unlikely.

    I will have a look at the ebook, but was told before that my air vales were not listed?

    Do you know a good source for main air-valves?

    Thanks very much for your help so far
  • Jamie Hall
    Jamie Hall Member Posts: 22,952
    Is it possible

    that there is an uninsulated section or a sag on the main that isn't heating so well?  That could happen -- and that could do it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
This discussion has been closed.