Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Leaking steam radiator relief valve

We have a steam system in an older house (1930s). Radiators in the basement and garage are on the ceiling, above the level of the boiler. The very large garage radiator is spilling water from the relief valve--a gallon or two per day when the boiler is coming on regularly. Our plumbing and heating service has tried replacing the valve a couple of times, using different sizes, but that hasn't helped. Someone has suggested that the radiator may be clogged and need to be descaled. Does that sound reasonable? And if so, how would we go about finding someone to do that? Any other suggestions?


  • RodRod Posts: 2,067
    edited November 2011
    Flooding Radiator.

    Hi- It's not likely that it is "clogged" or "scaled". We need to know a little more about your steam system. What type of steam system do you have - one pipe or two pipe?   What is the maximum pressure that your steam system runs? Residential steam systems should at under 2 PSI or lower. (Lower = better)  Has this radiator ever worked properly? The valve (vent) that is on it now do you have a name and /or a model number? (If you can't find one take a close up picture of the valve)

    It would also help if you posted some pictures of the radiators so we could get a look at the piping.

    - Rod
  • Home_OwnerHome_Owner Member Posts: 6
    Leaking radiator vent

    Thanks for your reply. Photos of the radiator, the leaking vent, the pressure gauge on the boiler, and the boiler itself are attached. The boiler is a Lennox gas-fired steam boiler, model CSB or CVSB. We couldn't get the whole radiator into one photo but took photos of both ends. The boiler was off when the pressure gauge photo was taken. The vent dripped a little from time to time when we moved in 12 years ago, but last winter the leaking got much worse. 
  • dripping vent

    by the looks of your pressure gauge, i would guess the first thing to do would be to lower the pressure on the pressurtrol to a maximum of 1.5 psi, verified by a low-pressure gauge [0-3 psi,]. as these pressuretrols are often inaccurate, i would put on a vaporstat to keep the pressure below 8 ounces, with increased main [not rad] venting.

    the water in the returns will rise due to steam pressure 1.75 inches per ounce of pressure, starving the boiler of water, and triggering a low water condition, so that is 5psi X 16 oz. X 1.75 in of hidden water going where it shouldn't! i bet your radiators are as clean as a whistle inside, having been washed by this distilled water.--nbc
  • RodRod Posts: 2,067
    edited November 2011
    Need to Check Radiator's Slope

    Hi- Thanks for posting the pictures. They are a big help!

    As NBC stated lowering the maximum steam pressure would help.

     I think you also need to check the slope of the radiator. This is a one pipe steam radiator and even though it is on its side, it operates just like a regular vertical standing one pipe steam radiator in that it needs to have some slope towards the inlet pipe so that the condensate will be "encouraged " to flow out. Steam is a gas so "floats" in any direction, where as condensate (water) needs slope to flow.

    I'm guessing that this radiator is very heavy, so that over time, it may have settled a bit and lost its slope. I would use a long carpenter's bubble level and adjust this radiator so that it slopes very slightly towards what should be it's lowest point, the steam pipe. (See attached photo) This should then "encourage" the condensate (water) to return to the boiler.


    Could you post some more pictures of the steam piping on your boiler?  In the one you provided I couldn't see exactly how the steam piping is configured. This maybe producing what is known as "Wet Steam" which is steam that carries a lot of water with it.

    - Rod
  • Home_OwnerHome_Owner Member Posts: 6
    radiator vent

    Thanks for the recent posts, with good suggestions. Rod, I will post more photos of the boiler tomorrow. Homeowner.
  • Long Beach EdLong Beach Ed Member Posts: 686

    That's an air vent, not a relief valve. 

    I'm not sure of the orientation of the photos, but the nub on the vent has to be on the top. 

    If the vent isn't oriented properly, condensate will not drain from it and it will spit water. 
  • Home_OwnerHome_Owner Member Posts: 6
    boiler and radiator piping

    In response to your post yesterday, I'm posting additional photos of the boiler and radiator piping.
  • Vent orientation

    If the vent is not oriented properly, it probably never closes, right? It is hard to tell from those pictures though.
  • Home_OwnerHome_Owner Member Posts: 6
    Orientation of vent

    The vent is oriented with the opening on top. - Homeowner
  • Slope

    What is the slope of the radiator? Is the end with vent closer to ceiling than the other one?
  • RodRod Posts: 2,067
    edited November 2011
    Over Head Radiator

    Hi - This is an overhead radiator attached to the ceiling so with that in mind, it would seem that the radiator vent is oriented properly. 

        I've attached a photo which I have labeled. The item I marked as "support hanger"  I'm assuming this (and other like it) holds the radiator in place(?)  If so you could adjust the slope just by putting some shim blocks between the support and the radiator. As I mentioned earlier the slope doesn't need to be much, just enough so that the water will flow towards the inlet pipe.

        Lennox boilers are made by Dunkirk and are very similar to the Dunkirk Plymouth steam models. Here's a link to the Plymouth model manual which might be of interest to you.

    Your boiler piping generally seems okay though you might want to check sizing etc. against the Dunkirk manual recommendations. You might also want to insulate the boiler piping . I finally did this to mine and was surprised what a difference it made with even that small area of insulation. When you check the radiator slope let us know how it turned out.

    - Rod
  • Home_OwnerHome_Owner Member Posts: 6
    adjusting radiator slope

    Thanks for your detailed help! We will try to adjust the slope, as you suggest, and will consider the other options. We aren't reall do-it-yourselfers, but we're having trouble finding a contractor who is an expert in old steam systems. - Homeowner
  • RodRod Posts: 2,067
    Steam book

    Hi- It might be a big help to you to get a book that is available on this website in the "Shop" section. It's called "We Got Steam Heat!"  and here is a link to it.

    It's written for the homeowner new to steam heating. It has lots of pictures and diagrams and in layman's terms, explains the function of the different parts of a residential steam system and how they should operate  It's easy, humorous reading and in an evening or two you will be light years ahead in your knowledge of steam heating. It tells you what repairs you can do yourself and what repairs are best lefty to a pro. One of the biggest advantages is it gives you enough knowledge to know whether the heating professional  you are talking to really understands steam heating so it helps you avoid "knuckleheads" This book will save you money and help you end up with a comfortable and economical heating system. I highly recommend it!

    - Rod
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!