Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Main vents or dirty system?

Gerry G
Gerry G Member Posts: 48
You guys are a great resource!

I've been having a lingering problem in getting heat to all the rads in my house. I have a one pipe steam system, with two mains coming out of the boiler (pics below).

Main #1 is for the front of the house, and is in a loop, with a Groton #1 vent at the end of the loop - 80' total length (40' x 2), 3" pipe diameter.

Main #2 is for the back of the house, and is a straight run, with a Groton #1 vent at the end of the run - 40' total length, 3" pipe diameter. The condensate return on Main 2 runs along the floor.

The vents were replaced 2 years ago, when I got a new boiler. I don't know the size of the old vents.

The radiators worked fine before the new boiler came in. Last year, I called the guys who installed the system to complain that the heat wasn't even, but they said that the system was dirty. But even after skimming the boiler and cleaning it, the radiators didn't heat up, unless the boiler ran for an extended period. Since the thermostat is near a radiator for on Main 1, the boiler would shut off before Main 2 rads got hot. By this point, Main 1 rads were very hot.

This year, when I fired up the boiler, Main 1 radiators heat up much faster than Main 2. I drained the system 3 times, and that didn't really help. I then shut some of the Main 1 rads off to force more steam into Main 2, and on some rads, the water came out of the radiator vent. I checked the pitches of the radiators and they seem ok.

In my chceks, I took the radiator vents to see what came out. Even with the Main 1 rads off, it took a long time for steam to come from Main 2. But, when it came, it came in full force.

After searching the site, I'm guessing that I need Groton #2 for Main 2, but why would a smaller vent work on a longer Main 1, and not the shorter Main 2? Could I have water trapped somewhere in the system that's preventing steam flow?


  • gerry gill
    gerry gill Member Posts: 3,078
    venting is an issue yes,

    but looking at the boiler picture you posted, which mains takeoff pipe is heating real well? is it the first one to recieve the steam, the one before the turn in the header? what pressure are you running at? and what size is the header pipe? and what size does the manual call out for? also what size is the equalizer drop for the condesate in the header? what does the manual call out for?

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • Gerry G
    Gerry G Member Posts: 48
    hope I get this right

    The main that's heating well is the one that's bearing to the left in the picture. The one heading to the right at 90 deg angle is Main 2 to the back of the house.

    At full operation, the pressure gauge on the boiler shows 10 PSI. The pressutrol cut in is set at 2 psi

    The header pipe is 2 1/2" and is what the mnaual calls for.

    Manual calls for min 1-1/2" equalizer pipe, but I don't know what that is to check the size :)
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    10 psi????? If this gauge is reading correctly you have a problem. Your pressuretrol should not let the pressure go beyound 2 psi. (where you said it was set) this is even on the high side. If the system is running at 10 psi your vents will hiss like crazy and lock shut. You must get the pressure down between 0 and about 1.5 psi. Did they replace the pressuretrol when the boiler was replaced? I assume that the gauge is good if the boiler is new. LOW PRESSURE STEAM!
  • Gerry G
    Gerry G Member Posts: 48

    Everything on the boiler was brand new at the install.

    Yes, the vents do start hissing when the boiler fires up. I checked and cleaned the pigtail.

    The pressure goes up to 10 PSI within 5 minutes of the boiler firing up. I should let you know that I'm also running a hot water zone off this boiler as well. Could explain why the PSI is so high?

    As gerry gill surmised, the main before the end turn off heats up much faster.
  • Main vent sizes

    Start with TWO Gorton #2 vents on the long main and one Gorton #2 on the short one.

    I bet the pigtail has plugged up again, or the pressuretrol is bad. This needs to be fixed ASAP. The excessive pressure is probably slamming the main vents closed.

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Jacob Myron_18
    Jacob Myron_18 Member Posts: 11
    Boiler steam pressure

    I looked at the piping installation and from the view shown it appears the boiler was not piped according to manufacturer spec.

    Steam pressure in a one pipe steam system should not exceed 2 psig.

    2 psig is plenty for your hot water loop. At psig the water temp is about 215 degrees. Typically most water heating systems do not exceed a 180 degree water temperature for heating.

    The first thing you want to do is lower trhe steam pressure to 2 psi and set the the pressure diferential at a 1/2 pound and see where that takes you.

    If you want you can e-mail me better pictures of the boiler piping installation and tell what results you had when you lowered the steam pressure.

  • Gerry G
    Gerry G Member Posts: 48

    Thanks for the reply. I'm guessing that I can tee off the main for the vents and not tap the main. My local supply place doesn't have Gortons. They have Dahls. Is there a big difference between the two.

    I've cleaned the pigtail three times, and it seems fine. I just skimmed the boiler and it was very dirty before. Now, the water coming out of the skim port is clean.

    Could there be something clogging up the PSI gauge that it's giving an incorrect reading. It jumps up to 10 PSI very quickly after firing up, thus I'm thinking that the gauge could be bad.

    Thanks in advance
  • Gerry G
    Gerry G Member Posts: 48

    Good news is that it doesn't look like the boiler was operating at 10 PSI. The bad news is I don't know the actual pressure, as the new gauge doesn't register any pressure at all.

    In my attempt to remove the old gauge, the brass nipple snapped, as the nipple thread was basically welded to the boiler. After working with an easy out and a drill, I was able to tap a new brass nipple into the boiler with a new pressure gauge. But now, the gauge is not registering any pressure.

    The pressuretrol is set at 2 PSI, with a cut-out of 1. The pigtail has been cleaned out several times. It shuts down the boiler within 15 mins of operation.

    Next step is to find Gorton #2s at a local place and see if that helps. I've skimmed the boiler once, but sounds like I need to do it again, and perhaps flush the lines from the attic.
This discussion has been closed.