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.

Steam Leaving Supply Valves?

I am suspecting that I have steam escaping from my Mouat radiator supply valves. Here's the evidence:

1) I am using several gallons of water a day

2) Prior to the weather getting very cold I serviced all of my radiator valves by taking the handle off and then making sure they were able to be opened all the way. Previously an installer or servicer of the system used the Mouat valves external rotatable disk to only allow the home owner a small amount of movement of the valve handle. In an attempt to get steam to fill radiators more quickly I made it so all the valves could be wide open.

3) Since that time I have been trying to balance the system using the Mouat orifice valves. Since none of the traps are working I am hoping to get the orifices open just enough to let the radiator fill about 90% with steam on the longest burner cycle (about 25 minutes).

4) Since this winter has been much colder than others, and I am keeping the house warmer than other years too, I can't say for certain that my servicing of the valves caused any problems - but it seems too coincidental to not be the case

5) Last night I used the valve handles to restrict the orifices of two radiators in my bedroom. The room stayed at the correct temperature, but the traps did not feel like they were seeing steam as they were not as hot as they had been in previous runs.

6) The sound of the steam entering those two bedroom radiators was significantly different. This could be because the orifice was smaller.

7) I used about twice as much water last night as I had previous nights. Yes it was very cold, but I do not believe the boiler could have run too much longer than any other previous night with the CPH set to 1 and cycles being very consistent at 25 minutes before cut out from vaporstat.


Q1) How likely is it that moving the handles on the valves to allow more or less steam into the radiator is causing more or less steam to find an avenue out of the valve and into the open air of the house?

Q2) Is there any test that I can run to see if steam is in fact leaving the system through holes in the radiator valve? (cold metal pot held over the valve for a few minutes and see if there is condensate inside?)

Q3) If we assume that there is no crack in the boiler are the valves the next logical place to look for leaks? Where else should I be looking?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,564
    Water loss

    I would think the graduated valves would accomplish the same thing as an orifice in the inlet, only so much more conveniently! Why not return them to their original settings, and see if there is any change in water loss?

    The 2 ounces or so which should be in your system is not going to blow a significant amount of steam out without some trace.

    The test for a leaking boiler is to overfill it to above the water line ( when only warm). Let it sit for a few hours, and then look in the firebox for any signs of leaking. Also check any returns while the boiler is steaming for wisps of steam or dripping.--NBC
  • butlermog
    butlermog Member Posts: 50
    If I could, I would...

    If I was a smart man I would have taken detailed notes on the position of everything before I messed with them. But at the time, since I thought I was doing the smart thing by opening the valves all the way up, I never thought that I would want to restrict them back again. Lesson learned.

    You're right that these valves should be exactly like using orifice plates in the inlet, but a bit more convenient. I have just not found the secret to correctly balancing them all yet.

    I have just read this article:


    which is giving me great hope that I am on the right track, but am still not sure the best practice on getting each radiator's valve dialed in correctly.

    So far I have just been feeling the trap side to see if it is as hot as the supply side. If so, I dial it down. Perhaps I should instead dial them all down fairly low and then open them slightly if the radiators don't heat all the way across.

    Any advice on finding the right settings from someone who has had to do this would be greatly appreciated.

    The other thing I have convinced myself of is that I believe I want the valves in the room where the thermostat is to remain mostly open so that the call-for-heat is satisfied as soon as possible. Does that sound right?
  • Jamie Hall
    Jamie Hall Member Posts: 18,923
    Patience, I am told

    is a virtue.  You are going to need some -- but the results will be worth it.

    First, though, you need to find out where the water is going.  "Several gallons a day" is way too much water loss, and unless your system is truly immense it is unlikely that you could be losing that through your valves.  NBC has some good suggestions for finding the leak or leaks, but you do need to get that straightened out.

    Second, make sure that your venting is adequate (at the very least) and your pressures are low enough.  Your Mouat system should be able to operate at no more than 6 to 8 ounces cutout on a vapourstat without the system cycling on pressure, except on very long runs (coming out of a setback).  If it is cycling on pressure on shorter runs, you need to add venting (always assuming that the vapourstat is calibrated properly -- a low pressure gauge may be helpful).

    Once you have done that, you can start resetting the radiator valves.  NBC is exactly right in saying that the valves serve the same function as orifices, only with the benefit of being adjustable for circumstances.  Adjustable, that is in only one direction: down.

    Assuming that you have accomplished items one and two above, then each radiator can be adjusted by itself, and the procedure -- though a bit tedious -- isn't hard.  Simply close the valve down until the radiator gets hot most of the way across and down on a nice long run.  You will probably have to do this several times -- get a rough cut on it, and then go around and do it over again, perhaps several times, because as you close one radiator the next one over will get a little more steam, and so on.  Once you have done that, make a note of some kind of the valve setting.  Perhaps a thin paint or marker line on the valve, even.  Then you can think about closing selected radiators down, if certain spaces get too warm.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • butlermog
    butlermog Member Posts: 50
    Thanks For The Tips

    Jamie and NBC thanks as always.

    #1) I am hunting for this/these leaks with all my knowledge and strength but have had no 'AH-HA' moments yet. I have flooded the boiler (although I have not left the water in there for several hours) and have seen no water on the floor of the boiler room. The valves were my next thought especially since the water use was higher last night after only adjusting the valves on two radiators.

    #2) Venting is maximized. Currently there are 2 Gorton #2 vents on the dry return and a Gorton #1 and two Hoffman 75s on the mains. Once the weather changes and allows me more than 30 minutes to work I am going to move the Gorton #2s to the mains and leave the dry return open. Vaporstat is set at 3oz cut out. It only gets there after 18 minutes of burn time which is enough to fill all the radiators. Once I get the valves dialed in that time might actually go down.

     #3) These Mouat valves have these great little plates that you can move once you find the right setting that will stop anyone from opening them farther than they should be - so once I get them dialed in I should be safe from my kids playing with them and wrecking the performance.

    Q1) If I do find steam escaping from the valves, should I be looking at the threaded connections to the supply pipe and radiator? If so, would thread tape be my go-to tool?