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New steam boiler owner - Question about water level.

So I finally took the plunge and bought my dream house at an outstanding price (thanks to the real estate market. Every cloud...). During the inspection I THOUGHT I paid close attention to the tutorial on maintaining the boiler. So here I am, the heat is kicking on for the first time and I'm listening to the valves hiss and radiators clang; I start thinking to myself: "Hmmm... This thing must be generating a decent amount of pressure. If something is wrong, it'll be like a bomb going off in my basement." So I walk down to have a look at the old guy and see how it's going.

Flash back a few weeks to September 30. I flushed the system as instructed (I was told once a month when the boiler is not in use, and once a week during heating season). I loosened the valve at the top of the site glass, and opened the drain valve until the water had left the site glass. Then I closed the drain valve, the valve at the top of the site glass, and started to fill the boiler. While it was filling, I noticed that the water level in the glass was not rising in proportion to the amount of water that seemed to be going in, so I opened the valve at the top of the glass thinking that it must be building pressure and not allowing the water to enter. Once I opened the valve, the water level jumped almost to the top of the glass. I turned off the fill valve, drained the water until it was at the mark in the glass, and then closed the valve at the top of the glass again. I thought that I had it all figured out.

Back to this evening. I flip on the light in the boiler room and see that the pressure valve is hovering around 2, the water is all the way up to the top of the site glass, and water is dripping (slowly) from the top (closed) valve on the site glass. This doesn't seem right to me, so I turned down the thermostat and opened the valve at the top of the glass and the water level immediately sank down to just a little below the fill line. Then I closed the valve again.

Info on the boiler: It is a Utica oil boiler which has been converted to gas.


1) Should that valve at the top of the site glass always be closed?

2) How should I purge the system?

3) Should I completely empty the water when I purge the system?

4) Does this boiler look old to you?

Thanks in advance!



  • Rod
    Rod Posts: 2,067
    edited October 2010
    Answer to Questions

    Hi Mark-

       Welcome to the world of steam heating!   First of all I'll try to answer your questions and then give you a bit of an explanation.


    1) Should that valve at the top of the site glass always be closed?

    Ans: No! Both valves (See labeled picture) marked "B" And "C" should be open

    at all times especially during operation,They are just closed when maintenance is done on the glass tube.

    2) How should I purge the system?

    Ans:  I'm not quite sure exactly what you mean by "purge" (See remarks on Low Water Cut Off below).

    3) Should I completely empty the water when I purge the system?

     Ans: Again not quite sure what you mean here. (See remarks on Low Water Cut Off below.)

    4) Does this boiler look old to you?

    Ans:  Yes

    I took the photo you provided of your boiler and added some arrows and letters to it to help in the explanations.

    Letter "A" is the pressure gauge. Residential steam systems operate at a maximum pressure of 2 PSI or lower.

    Letter "B" and "C" are valves at each end of the sight glass. As mentioned above they should be open at all times.  The design water line (where the water line should be when the boiler is not operating) is about half way up the sight glass. ( I think this is what you maybe calling the "Fill Line")

    When the boiler is operating the waterline in the sight glass will drop but should always be visible. This drop is normal.

    Letter "D" is the pressure controller. This shuts of the burner when the steam  pressure reaches the maximum set level (should be not greater than 2 PSI). When the pressure drops below a lower set level, the controller turns the burner back on.

    Letter "E" is called the Low Water Cut Off. This is a safety device and shuts off the burner if the water level in the boiler becomes too low. It has a float switch inside it and it is obviously very important that this switch works properly at all times. Letter "F" is the Low Water Cut Off - "Blow Off" valve. The Low Water Cut Off should be "blown down" once a week.  To do this, you open the valve (Letter"F") carefully/slowly while the boiler is operating and allow the boiler water to be released. The idea is to blow off any dirt accumulation that has built up in the Low Water Cut Off as this might cause the float to stick and not operate. It's a good idea to blow off enough water to test the operation of the Low Water Cut Off by allowing enough water to blow off so that the water level drops low enough to shut off the boiler /burner. When the burner stops, shut the blow off valve and then add enough new water to bring the water level back to the design water level in the sight glass.

    New water contained dissolved oxygen  which is very corrosive to boiler so always bring the boiler to a boil (make steam) so the dissolved oxygen is boiled off.

    Other than to replace the water released in the weekly LWCO (Low Water Cut Off) test, properly operating boiler uses very little water and generally boilers normally are fully drained and refilled about once a year.

    A couple of things might be a big help to you. One would be to get a book that is offered on the website titled "We Got Steam Heat" 


    It's written for the homeowner new to steam heating. It's easy humorous reading and  a couple of evening of reading will put you light years ahead in you knowledge about steam heating.

    After you read the book I would get a steam pro in to check  your system and answer any questions you have. You might want to take a look in the "Find a Contractor" section at the top of this page. Scroll down past the zipcode section to the "States" section and see if there is a pro listed local to you. There are some very good steam guys listed there.

    I hope this has answered some of your questions. If you have more we'll do our best to answer them.

    - Rod
  • PurdueMark
    PurdueMark Member Posts: 2
    Thank you!

    Your reply was a huge help. I'll run out and get that book right away too!
  • Rod
    Rod Posts: 2,067

    Glad we could help! "The book" will REALLY help you!   You also might want to take a look at what Dan calls "Off the Wall". Go to "Resources" at the top of this page and look there. Lots of good info. Read Dan's Article Archives- These contain articles on residential steam that he wrote for heating periodicals. Give you something to read while you way for the book! :)

    - Rod
  • BklynJoe
    BklynJoe Member Posts: 3

    Your response was a MASSIVE help (new homeowner, whole system is new to me, firing up steam boiler for first time).

    I notice in your response you mention that new water contains oxygen which is detrimental to the boiler. Make sure it's on and creates steam to prevent problems.

    How serious of an issue of this? Suppose the boiler was to sit off with 'fresh' water in it for an hour? a day? a month?

    Thanks in advance. (We Got Steam Heat in my cart!)

  • BobC
    BobC Member Posts: 5,473
    Good practice

    Your boiler probably has thick castings compared to modern boilers so it is more robust when it comes to corrosion.

    If a boiler is not used to heat hot water during the summer months water should not be drained or added. When the boiler is in use a float type low water cutoff should be blown down every week or two and water added to makeup any water lost because of the blow down. This should be done while the boiler is in operation to help remove anything on the float and because heating the new water up will drive off any oxygen in the water.

    Driving off oxygen is very important with modern boilers because they have thin castings, your boiler is more robust (and probably less efficient) so it isn't as critical but it's a good habit to get into. The worst thing that can happen to a steam boiler is that it gets ignored, blowing it down on a regular basis will allow you to look it over to make sure there are no leaks or other signs of trouble.

    So the answer is that you should not add fresh water if you cant run the boiler within a reasonable time - say an hour. If you don't meet that mark occasionally it won't matter but don't get into the habit of adding water and not running the boiler. Sooner or later you will have to replace that boiler so developing good habits now will make sure any new boiler lasts a good long time.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    LWCO blow down techniques

    Generally I open the valve under the LWCO and let the water run, until it changes from mud to clear. This is enough to cause the burner to cut off, and to get the sludge out of the float chamber.

    In winter,I do this a couple of times a month. My boiler has 2 lower trappings, piped over to a floor drain, and I let about a gallon of water out of each every other month during the heating system. There is no real need to drain the boiler, unless you are trying to remove chemicals, as water never wears out.--NBC
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