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Cold riser

I have a 4 story building with a steam boiler. Everything has worked fine for years. This year we are having a problem where the riser in the far corner of the building does not heat. The main line in the basement goes to the rear and then branches left and right for each side of the building. The left side works fine but the right side gets steam about two feet past the branch In the basement and then stops. It never makes it out of the basement.

We added a vent at the end of this branch before it turns up and the steam doesn’t get to it.

If I shut down the boiler for a couple hours and then restart it everything works properly with heat getting to the top floor for a short period of time but then the issue returns.

We thought there could be an issue with the condensate not draining properly but we opened the pipe and there wasn’t any backup of condensate.

Also of note: we have a tekmar system to control the heat that senses the temperature on the top radiator in that line. It runs the boiler to “establish steam” but since the riser isn’t heating it continues to run the boiler. So this isn’t an issue of the thermostat shutting down the boiler before the steam reaches the far radiators.

Also, the pressure on the boiler is reading 0 but I don’t see any obvious leaks anywhere. Not sure if it’s just an issue with the gauge or if there isn’t pressure. The boiler doesn’t appear to be cycling off.

Thanks in advance for any thoughts on the issue.


  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    If that vent you added doesn't see steam (but does work) there is something in the pipe blocking the steam. Before you get radical, try running the system (with someone at the boiler to turn it off) with the vent completely off -- just an open hole.

    Then if you still don't get steam, go back along that pipe. You may have a sag in there somewhere which is trapping enough water to defeat the steam. Wouldn't be the first time.

    The only reliable way to check pressure on residential systems is with a low pressure gauge -- 0 to 3 psi. You can add it alongside either the pressuretrol or the existing 0 to 30 psi gauge (which has to stay there for insurance and building code).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,846
    Check your firing rate. It might need to be adjusted.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Ben_13
    Ben_13 Member Posts: 5
    Update on this issue. We took off the gas valve and it had crap built up in it that was restricting the amount of gas getting to the burner.

    It must have been happening slowly over time and caused the flame to eventually weaken to the point where it wasn’t creating enough pressure to get the steam up the far riser.

    After it was cleaned out the steam was substantially stronger and everything is working very well.

    Thanks for the suggestions!