Oversized radiator - air locking system solution

Jyepez

Hello heating help community,
Posting here after using the steam book and this forum heavily last year to learn, understand and find solutions to our heating issues. 
Last winter we switched our single unit oil- steam boiler to two gas-steam boilers ( crown 135 kbtu) in a two family, 3 story house.
The system is an orginal richardson- two pipe system. The system had two zones or mains, one for 1st floor, one for 2nd floor and attic. We split the system respevtively for the unit piping system. 1st floor worked fine from getko. On 2nd/3rd floor we added one gorton #2 at end of long main, and 1 gorton #2, and 1 gorton #1 for dry return.  This solved the venting - air locking issue we had with radiators on long run of main. Ths system heats rather quickly, at thermostat, heats up 5 degrees in 1 hour. All radiators are heating except for one oversized radiator at end of short run.
There are three radiators on short run,  1 on 2nd floor and 1 in attic that get adequate heat. The last radiator on run has always been cold even with the previous oil- single burner system except one time when the boiler ran for a really long time- (tstat was set really high accidently).
I tried to get steam to that radiator by installing a gorton #1 next to the inlet valve. Didnt work, added a mistomaid D to see if it helps. Nada.  The reason why i added the vent next to the valve and not in the basement is because the area is an addition, and there is no basement, just unconditioned crawl space, which I didnt want to touch.

I found another possible solution on youtube- airlocking the returns with a zone valve until steam gets to radiator, a sensor triggers temperature set then opens control valve for venting system. 

https://youtu.be/7B9AUJi4_sg?si=ZIIuLnUNfNl9CjpE


What are your thoughts on diagnosis, and solutions?

KC_Jones

If you are doing all that venting and steam sill isn't getting there, I doubt it's a venting problem. Presents to me like you may have a sagged or incorrectly sloped pipe leading to that rad, or in the main before that rad holding water and blocking steam flow.

You have as much venting as I have on an entire 20' long 2" main, and that vents in under 3 minutes.

I just read your post again for any clues I missed on first reading.

" The reason why i added the vent next to the valve and not in the basement is because the area is an addition, and there is no basement, just unconditioned crawl space, which I didnt want to touch."

I'd say another possible issue is that pipe leading up to the radiator in the unconditioned space is condensing so rapidly that the steam just never makes it during a typical run time. You also mention it did heat once on a really long run time, which would make sense if this is the issue.

Insulate that pipe very well and then see what happens. I would speculate if the pipe pitch is correct, and you insulate the pipe, you may solve the problem. Normally we recommend 1" of insulation, but if it really is a completely unconditioned space under there, I'd be inclined to go thicker, but that's just me.

Jyepez

The pipes in the unconditioned space are well insulated. I believe if steam was condensing in that stretch, there  would water hammer the pipe and i would hear it but no water hammering. 

Jyepez

Thank you KC jones, i started shimming the radiator to raise the pitch. It started gurling and eventually steam reached the radiator. The floor had settled nearly 3" in this extension of the house in relation to main house.