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.

Cold convector (steam) after vent replacement

aat879 Member Posts: 17
I have cast iron convectors recessed into the walls on a one-pipe system in a two-story single-family home. Last year, after buying the house, I went around and changed all the vents, most of which were either blocked or horribly rusty, with Hoffman straight steam convector vents (#41 and #41 depending on the shank size).

For several of the cold convectors, it made them work like magic. For a couple that were sluggish, they have stayed sluggish (that's a different troubleshoot I'll probably put in a different thread). For one convector in particular, it took it from getting hot with a routine water hammer in mid cycle to totally cold. That's what I want to focus on.

I have attached a couple of photos. The vent there is the old one that I replaced. I'll check the new vent to make sure it's opening and closing properly, but I believe it is. What could be the problem? Is the fact that that convector consistently had water hammer—manifesting as a single thud somewhere in the middle of the cycle—relevant? Maybe there's old condensate sitting in the convector, but even if there is it's not clear why the new vent would cause it go cold.

The big challenge is that, because the convectors are recessed, it's hard to really see whether the pitch is off. But these things are really tightly secure in their housings and almost impossible to move, so I don't imagine it has sagged.

Appreciate your help.


  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    Can you treat sort of as you might something lost? Go back to where you last saw it. In this case, go back to the steam main that feeds it. Then follow the runout to it. Is there somewhere along there -- perhaps all the way to the valve -- which gets at least vaguely warm, and then stops and is cold from there? If the whole thing is cold, something really is blocking the air -- and it could be a wonky vent. Or the valve closed (once in a while they do work...). but you might find a sag in a pipe or somesuch...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • aat879
    aat879 Member Posts: 17
    edited October 2021
    Thanks. Unfortunately that part of the main was foolishly put in a pipe chase by a previous owner that makes it difficult to inspect them. Since the radiator got hot before, I’m hoping it has something to do with the radiator vent. I just pulled it off and blew through it, so it’s not blocked. Valve looks like it opens and closes fully, but I can only tell by spinning the handle. There was a small nipple put in the convector’s vent threads, to which I added a small coupling so I could screw in the vent. So I’m trying to see if there’s crud in there. Some pictures attached.
    EBEBRATT-Ed Member Posts: 13,440
    It's possible you supply valve is stripped, broken internally or the disk fell off and is blocking the pipe
  • aat879
    aat879 Member Posts: 17
    Thank you @EBEBRATT-Ed. I’m not convinced that’s it, since I feel some resistance when I twist it. But I’d like to test it. What I’m thinking is to twist the valve to fully open and turn the boiler on. If no steam comes out, then the valve needs fixing. If it does, then I run and shut the boiler off, or have thick heat-resistant gloves ready and quickly screw on the vent.

    Is this overly dangerous to do? I’ve dealt with hissing vents but not an unfilled radiator tapping.
  • aat879
    aat879 Member Posts: 17
    @EBEBRATT-Ed. You’re right, it’s almost definitely the valve. I took a risk and turned the system on with the air vent out, ready to plug it.

    Problem is that the valve, like the convector, is recessed in the wall. The body of the valve is only partially exposed, but the bonnet on up to the hand wheel is accessible. Picture is attached.

    What I’d like to do is loosen the bonnet and carefully pull out the assembly and see if I can pull the disk free and hopefully set the valve to permanently open. My fear is that, if I’m not able to extract the blockage, I won’t be able to return the bonnet assembly with a full seal. One plumber said I’d be able to put some dope on and re-seal it. Another said it’s risky because these parts are old and the bonnet might not screw back on tight.

    Is this something okay to try? I don’t want to be stuck with an opening in the system, but the room this is in (the bathroom) gets very cold. Is it also possible to get a plug as a backup?

    Any others have thoughts? @Jamie Hall? @Steamhead?

    Thanks so much. I now know that I should never have screwed the service valve shut to begin with. Live and learn.
  • delcrossv
    delcrossv Member Posts: 502
    I think you're stuck with removing the bonnet and poking around inside the valve. If you can get it off, there shouldn't be any reason you can't get it back on.
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
    EBEBRATT-Ed Member Posts: 13,440
    edited November 2021

    Yes you can unscrew the bonnet. Use big enough wrenches that fit well and put one on the valve as well as a back up on the valve for more leverage and so the valve will not turn. Expect it to be difficult to break free.
  • mattmia2
    mattmia2 Member Posts: 7,736
    Maybe you managed to move the whole convector such that the supply pipe dropped and is now trapping water?