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Steam Boiler Boils off all Water In 30 minutes

I am a homeowner with a problem my plumber seems unable to solve. My house is about 80 years old, and my plumber installed a new Burnham boiler 9 years ago. The problem is that the after the boiler runs for about 20 minutes, the low water cutoff value turns the boiler off, then proceeds to inject new water into the boiler. My plumber said the return lines were likely the problem, so he replaced about 70% of the basement level returns, going away  from the boiler (the remain portion of return line is in a crawl space, and because the portion replaced is lower and closest to boiler, the plumber reasoned it would be the most constricted). Anyway, this repair did not solve the problem--I do hear water returning through the new return line.  To understand the problem, I have been manually cycling the boiler. I let it run for about 20 minutes, watching the sight glass, and just before the level is below the low water cutoff, I turn the boiler off. Within 7 minutes, the water level is restored to where it should be (about 3/4 high in the sight glass, and well about the low water cutoff). It would appear that the problem is that the water is not returning to the boiler fast enough, but when I looked at the return pipe that was replaced, it was not impressive in terms of the amount of restriction. So I am not convinced the problem is constricted returns. Does anyone have any ideas as to how to solve this issue, or what could be wrong? Also, one other question--the maintenance tech sent by the plumbing company for annual maintenance said that adding a lot of fresh water (e.g, a gallon)  often is bad for the boiler--is that true?


  • Jamie Hall
    Jamie Hall Member Posts: 20,804
    last things first

    Yes, adding a lot of fresh water all the time is bad for it.  On the other hand, running a boiler dry is worse... and flooding it isn't a solution either.  Something must be done about the slow return.

    First question I would ask: what pressure are you running this thing at?  Water can't return to the boiler if the pressure in the boiler is keeping it out!  The pressure should never be higher than two psi, and lower is better.  If you have a pressuretrol, it is very likely that you can't set it much lower, but try setting it at 1/2 psi cutin (as low as they will usually go reliably) and a differential (additive) of 1 psi, so it should cut out at 1 1/2 psi.  See if that makes a difference.

    If it doesn't, I'm sure we can come up with some other things to try.  It's possible that there's an obstruction (7 minutes to return all the water is a little long) somewhere, but that's not the only possibility.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • slow return

    i agree with jaimie that high pressure is the likely culprit here, and the only way to check that accurately is with a good low-pressure gauge [gaugestore.com 0-3 psi]. mount it in addition to the code required 0-30 psi gauge, on the same [copper/brass] pigtail as the pressuretrol, which will protect it from the steam. a plugged iron pigtail can cause the pressure to rise out of control, because the pressuretrol is unable to "feel" the pressure

    this would be a good time to make sure your mainline [not radiator] vents are fully functioning, and capacious, as the air in the system can exaggerate this symptom, before it has left the pipes, through the main vents.

    also check to make sure that there are no horizontals in the returns close to the waterline of the boiler, as these can "hide" a lot of water while steaming. the dry returns should drop vertically down to the floor, below the boiler, as they become wet and horizontal. i would turn the auto-fill off, and run the boiler without it, so you can see if you are losing any water.

    i also recommend you get a copy of "the lost art of steam heating", so you can understand these systems better, and learn to do your own minor maintenance/diagnosis.--nbc
  • derwood50
    derwood50 Member Posts: 10
    Thanks for advice--Pressuretrol Question

    Thanks for the quick answer. The boiler does have a pressuretrol  control--I will check it to see if it works--one question regarding the pressuretorl--if it kicks the boiler off because the pressure is too high, how long should it take for the pressuretrol to allow the boiler to come back on (this is a honeywell mercury switch pressuretorl)?

     Also, I have noted the pressure gage indicates that it never goes above 1 PSI before the water is just about at the low water cutoff point--do you think that is enough pressure to keep the return water from getting back into the boiler?
  • derwood50
    derwood50 Member Posts: 10
    Thanks Nicholas

    I am ordering the book now
  • original gauge= paper-weight, or christmas tree decoration

    the 0-30 original gauge is useless for our purposes, although it is required by code. if it is off a few percent, then that 1 psi shown could be higher, and if is not on the same unobstructed pigtail, the the pressuretrol won't realize what the actual pressure is.

    for every ounce of pressure, the water in a manometer, or returns;  the water will rise 1.75 inches! a column of water of several feet height, by 2 inch dia. will be quite a bit of water which is unavailable to the boiler, until the pressure drops at the end of the cycle.

    i could also say that the original pressuretrol is not as good at maintaining the needed low pressures as a vaporstat, for steam heating, but some people here have been having problems with those as well! it is always a problem when there is only one manufacturer making a much-needed device. with no competition, there is no reason to be concerned about quality!--nbc
  • Jamie Hall
    Jamie Hall Member Posts: 20,804
    With regard to timing

    if the radiators aren't all hot yet, it is surprising how fast the system pressure will drop after the burner stops.  A minute or two -- or even less -- for a 1 psi drop isn't uncommon, even in bigger systems.

    NBC's comments on the possibility of a stretch of return holding a lot of water are right on -- and the stretch in question could be quite some height above the water line, if the pressure is too high.  Note that 1.75 inch for each ounce: if you are running at, say, 3 psi for some reason, that translates to 44 inches or so -- and unless you have a very high basement, I'll bet your dry returns are lower than that!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • derwood50
    derwood50 Member Posts: 10
    More Questions After Your advice

    Thanks for help.

    Last night I adjusted the pressuretrol to cut out at 1.5 psi--I referred to the insturctions on this site, and i downloaded the HoneyWell Install manual for my particular Pressuretrol, so I am confident the adjustment is correct.  That said, I can't test the pressuretrol as per the instructions in the Honeywell manual because the boiler burns off the water below the low water cutoff in about 15 minutes--and the main gauge on the boiler has barely begun to move--at this point it is about 1 PSI.   I assume adding water at this point in order to continue buiding pressure makes no sense, since I clearly have a problem, so testing the pressuretrol at this point should not be the main focus--do you agree?

    So, from what you guys said, i take it the best course of action at this point is to get a 3 PSI gauge, and install it using the pigtail feeding the pressuretrol--then test the system again--and the idea is to see if the pressure is higher than 1.5PSI--and if so, that would point to water being retained somewhere in the returns--do I have this right in terms of the next logical step?

    This question is jumping the gun--but assuming the evidence does point to water being retained, how does one prove it without having to cut into the return line? There is a horizontal stretch in a crawl space that is above the boiler--so from what you guys said, that could be where the problem is--I am just wondering if there is any solution short of cutting the line to see what's going on, given how costly that step is.

    thanks again for the help
  • Jamie Hall
    Jamie Hall Member Posts: 20,804
    Slow progress...

    but by remote thinking, it's bound to be slow.  Where are you located?  You might try seeing if there is a good steam man in your area -- try Find a Professional on this site, but keep in mind it doesn't always work quite right yet.

    That said, I presume that line in the crawl space is a return, and we are talking two pipe steam here?  What is the elevation of that line in relation to the elevation of the water line in the boiler?  That is, how high is it above the water line in the boiler?

    I must admit that what really puzzles me about this one is that apparently the system worked fine for nine years, and then suddenly developed this problem.  What, if anything, changed about the time the problem developed?

    Sounds like you've got the pressuretrol under control, anyway!  Further testing of that is probably pointless at this time.  I'm not even sure I'd bother with getting a low pressure gauge.  You certainly shouldn't add more water so you can build pressure, though.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • derwood50
    derwood50 Member Posts: 10
    More Info

    To add more color: this is a one pipe system. The horizontal stretch is approximately 3 feet above the boiler water line.

    As for things that changed over the last nine years, let me start by saying this problem has been going on for several years--in fact, i'm not sure the system ever functioned properly. I don't really remember whether I heard the automatic refill valve actuating often 9 years ago--but I did start to notice it several years ago, and knowing nothing about steam heat didn't think much of it. I assumed it was normal. But over time, i began to wonder, and finally asked the plumbers that supplied the boiler and that is when I began to recognize it as a problem. 

    It's worth noting that when the low water cutoff shuts down the boiler, and the auto refill kicks in, it seems to add only a small amt of water each time-e.g, a spurt--I think the return water gets back fast enough to stop the auto refill from pumping in too much water--thus the boiler doesn't get flooded.  The plumber suggested I have a leak, but I don't think I do because I marked the sight glass, and it always returns to the mark once the boiler is off.

    Having said that 2 major things have changed since the boiler was installed, and the timing does coincide with my becoming aware of the low water cutoff/auto refill issue--I renovated my kitchen and during this time the same plumber ran a hot water coil off the boiler for radiant floor heat--I don't know if this could be any issue--but that did change.

    One other change is this: I combined several rooms during the renovation, and there was one radiator that was no longer needed; so I just capped the pipe feeding the radiator--this was the pipe that went off the main--could that be an issue? Also, there is one radiator in the house that is cracked, so it's valve is always off--which I guess creates a similar condition in the system as the pipe I capped--could either of these issues cause a problem?

    Thanks again
  • low water mystery

    if you cut off the auto-fill, how long does it take for the waterline to be restored?

    check my math, but that 3ft. height of the far return above the waterline only takes 2.3 psi to raise water up that far! that is why i feel the accurate low pressure gauge to be so important, especially as the steam can move through the pipes with 2 ounces of pressure! and effect this high pressure, when existing, is magnified by the presence of unescaped air, causing back-pressure in the system. in other words, you can suffer the effects of high pressure more easily, with generous venting.

    i don't think you will have to cut into the line in the crawlspace; just verify that there isn't a broken pipe hanger allowing a sag.--nbc
  • derwood50
    derwood50 Member Posts: 10
    Low Pressure Gauge Question

    This weekend I plan to reconfigure the Pressuretrol such that a pressure gauge is fed off the Pressuretrol's  pigtail so I can accurately measure what the boiler is doing--can you guys advise me on the type of gauge I need--I planned on using one with a scale of 0-15psi.

    Is that the correct scale, or should I use on that is less than 15psi?

    Does it have to be especially designed for use on a steam boiler? 

    One other question--does the boiler steam condense in the pigtail, so the gauge is measuring water as opposed to steam?

    thanks for the help.
  • Pressure Gauge

    Most people are using  a 0-3 PSI gauge #33020 and these are available from the Gauge Store


    The gauge should have a pigtail as this protects it from live steam. Several people have asked about the gauge being only rated for 140 F -This is okay because the pigtail protects it.   The water in the pigtail as little affect on the gauge's measurements.

    - Rod
  • derwood50
    derwood50 Member Posts: 10
    Showing no pressure at the Pressuretrol Steam Siphon

    So, taking the advice of NBC, I reconfigured the Pressuretol such that it was side by side to a pressure gauge--e.g. the pigtail connected to a T, then 2 nipples--the gauge on right, the Pressuretrol on left--I also used a 4" nipple from the boiler to the pigtail, and connected the pigtail to nipple with a coupling. The gauge is new, max's at 15 psi (the plumbing supply had nothing lower/more sensitive)

    I fired the boiler until the radiators had heat, and noted the main pressure gauge, which has a tap about 1" lower than the one for the pressuretrol --the main gauge was showing about 1# pressure----but zero pressure showed on the gauge next to the Pressurtrol--the pipes to the pressuretrol  were cold too--the nipple off the boiler was very hot, but everyting from the pigtail on to the gauge/pressurtrol were stone cold.

    So, i wondered whether the problem was too much air in the pipes. So, I took the whole thing off the boiler, attached the pigtail directly to the boiler (it is a new pigtail, so it's not clogged), then put the gauge on the pigtail. Fired the boiler up, and exact same thing--zero pressure on the guage. I left the boiler run until the main gauge was showing a bit over 1 pound, but still, nothing on the pigtail tap.

    Any ideas on what is going on here? I assume if there's no pressure for the pressuretrol, that could explain why the boiler just runs until there's not more water--it never cuts out due to a pressure rise. 

    But is there something about attaching a pressure gauge I am missing--e.g. did i do it wrong, and that is why there's no pressure at the pigtail? Am I right to assume zero pressure at the pigtail indicates a problem?

  • Missing Water

    Hi - I first must say that probably the best thing would be to go to the top of this page to "Find a Professional" and see if there is a steam pro local to you who could help you. Trying to guess what is wrong with a steam system without seeing it, isn't easy.

    As I see it we are possibly dealing with two problems here which may or may not be connected.

    Problem 1:  Low water conditions in the boiler. This could be caused from either a leak in the system or by just a slow return of the condensate to the boiler.

    If you could answer the following questions may it would give us a better idea of what exactly is happening. In the period before some of the piping was replaced, during the boiler's operation when the automatic water feeder added water to the boiler, what was the affect on the waterline in the sight glass after the burner had shut off and enough time had passed to allow all the condensate to return to the boiler?

    (Question #1) Did the water level rise above the normal waterline in the glass tube?

    After the piping was replaced, during boiler operation, when the automatic water feeder added water to the boiler, and after the burner shuts off and the condensate is allowed time to return, does (Question #2) does the water level rise above the normal design water level in the glass tube?

    If the answers are different that would indicate that the new piping had an affect on the water level.

    Problem # 2  Apparent lack of steam pressure.

    First  of all you must be building some pressure otherwise your radiators wouldn't be getting warm (steam)


    A: Burner is not provided enough heat to make ample amount of steam.

    B: Ample steam isn't being produced to due dirty boiler water.

    C: Pressure measuring equipment isn't working due to blockage and/or malfunction

    D: System (specifically the boiler) is leaking.

    Since you are now working on Item "C" above  (the pigtail/ gauges etc.) Let's check that out first.  I would say you need to take the gauges off the pigtail and inspect the pigtail /piping for blockage. I would also check the boiler port where the pigtail attaches for blockage. Use a coat hanger wire and make sure this passage in unobstructed by inserting it well into the boiler and wiggling it about to make sure the passage into the boiler is well open. Blowing into the new gauge and observing some movement in the needle should indicate the gauge is okay. With this done we should be fairly sure the gauge when attached to the boiler is able to measure pressure. (Air in the gauge pipes doesn't make difference as long as it doesn't leak out of the pigtail/ pipes)

    Question 3: Does gauge/pigtail/plumbing and gauge port in the boiler, test out okay?

    Next let's address item "D" specifically the  boiler leaking. Keep in mind this can be the boiler itself or anything attached to the boiler. (You mentioned a hot water heating leg)  Any leak could be just a small pin hole leak

    When the burner is operating check the chimney and see if any steam is coming out of it. This would indicate a steam leak into the fire box. Since it's winter and cold I'd hesitate doing the next test and that is flooding the boiler and checking for a leak. This is done with the boiler cold- NEVER HOT!  I believe you said that the pigtail is attached to a port in the top of the boiler. I'd remove this and insert a 4 inch long open nipple as when this overflows you will know the boiler is full of water. You then fill the boiler till it is completely full. Be careful to try and not get water on the boiler or floor as what you want to do is then wait for a period of time say 30 minutes to an hour and see if any wet spots appear indicating a boiler leak. After you finish that test remove the nipple and reattach what was ever connected to that pot. Be sure to drain the boiler water back to the design level.

    For Possibility "A"  - You will need to get a Burnerman to check this out as he has the equipment and experience to do this. Burners are an area best left to the pros! !

    For Possibility "B" -  Was the boiler skimmed after the new piping was added? It may be that a lot of cutting oil etc from the new piping has contaminated your boiler water.  You might want to take a sample of water from the boiler and boil it on the stove and compare that with boiling an equal amount of fresh water. (I have a friend who uses two glasses of water ,one boiler, one fresh, and boils them side by side in his microwave for comparison. I haven't tried this and since the heat doesn't come from the bottom like a boiler, I'm not sure how valid doing a boil test this way is.)

    At this point let's just check one thing at a time and find  the answers for questions 1 to 3 , check the chimney for steam and maybe do take a boiler water test.

    In reading over the information you have already provided, you haven't mentioned what the boiler's model is and also how many radiators there are in the system. That would help if we knew that.

    - Rod
  • TomM
    TomM Posts: 233
    Missing Water

    This quote strikes my fancy:

     and the timing does coincide with my becoming aware of the low water cutoff/auto refill issue--I renovated my kitchen and during this time the same plumber ran a hot water coil off the boiler for radiant floor heat--I don't know if this could be any issue

    are you sure he ran it seperately off the coil?  or is it using the boiler water?

    If he ran it using the boiler water, you might be taking too much heat to make steam, and, all the water might be in the clogged up PEX.  just a thought.

    -Tom Novice

    There was an error rendering this rich post.

  • mysterious disapearance of water

    can you temporarily cut off the radiant circuit to see what difference that makes? some where, i suspect the water is being "hidden" until  7 min. after shutdown; possibly in some horizontal part of the return, within the pressure raising height, above the waterline.--nbc 
  • No Water

    The lack of water has to be either from a leak or as we don't know if the original replacement installation worked properly, it maybe boiler capacity just isn't enough for a large system and needs a reservoir. The lack of steam pressure could be from a leak, the radiant portion sucking off too much heat, bad boiler water or the  burner settings are off.(I'm assuming the controls are okay)

    The questions in my previous post were to try to determine the answers to a few of the possibilities and eliminate them. Anybody think of other possibilities?

    - Rod
  • derwood50
    derwood50 Member Posts: 10
    Answers to Questions

    Guys, thanks for all the input. I did order the book The Lost Art of Steam Heat, but I have not yet received it--so I appreciate the answers to questions I may be able to find out myself through some reading.

    I will answer the questions raised in the above replies tomorrow--but I want to share with you an interesing development.

    When the plumber replaced the return line, he did not put on any pipe insulation. He said there was not enough heat loss to worry about that. The run he replaced is about 50 feet of pipe. Today I put insulation on the pipe--yesterday I measured the pipe temperature at the far end of the run, and it was about 160--then i measured it where it went in the boiler, and it was basically room temprature, so I figure that was enough loss to warrant insulation.

    So now, in the few hours since I did that, the boiler shows about 2 pounds of pressure on the main gauge, and the pressuretrol is shutting down the boiler as it should--it shuts down just before the low water cutoff would shut the boiler down

    Does it make any  sense to you guys why insulating the retrun line would increase the steam pressure? This is the first time Ive seen the main gauge get above 1 pound.
  • Unknown
    edited December 2009
    Insulation of the Return

    Good! You have made great progress!  Are your main vents on the end of the return rather than on the ends of the main? What's happening is the uninsulated return was acting like a huge radiator and using up all the steam. When steam collapses (turns back into water) a cubic foot of steam reduces to the size of a cubic inch of water. This creates a huge void and the corresponding vacuum. Your boiler was constantly feeding this vacuum. Now you are only producing the steam necessary to heat the radiators. The reason I asked you about how many radiators you have was that I thought that the system was bigger than your boiler's capacity and apparently it was though the cause was the "return radiator". Don't worry about answering the questions I asked as you have found the solution. If you are building steam pressure you are unlikely to have a leak.  You said "main gauge", is the 2 PSI registering on the new gauge?  I'd run your system like it is for a day or two just to get an idea of how well it is now working which should be a lot better now that there is plenty of steam for the radiators.

    I would then see how low you can get the pressure and still get steam to all the radiators. Start with a cutoff of 1 1/2 PSI and a 1 lb differential. Try that for a while and see how that works. If satisfactory then you can try lowering more though you may have to switch to a Vaporstat as the Pressuretrols get unreliable at the lower pressures. The lower pressure should also allow your system to catch up more easily so that you shouldn't have the low water problem. With the system now operating properly you should see a beneficial difference in your fuel bill.

    - Rod
  • derwood50
    derwood50 Member Posts: 10
    Thanks for all the help

    Thanks to everyone who gave me advice in solving this.

    If anyone in the future has a similar issue and reads this, one other note--i insulated the entire return, the 50' stretch replaced last year, as well as another 50' of original pipe in the crawl space.

    Right now the pressure hits just over 2 PSI when the pressuretrol cuts off the boiler--this is very close to when the low water cutoff kicks in--e.g, the water in the sight glass is very low--in fact I noticed that when the boiler shutdown due to the pressuretrol, the auto fill did make a few attempts to add water--so I shut the value off so it can't add any water--it takes roughly 2 minutes for the pressure to go back to zero and the Pressuretrol then starts boiler again--and this is enough time to bring the water in the sight glass up substantially.

    Rod, my main vents are at the far end of the mains--there are no vents on the return--this is how it should be correct?

    Again, thanks for all the help.

  • Main Vents

    The best place for the main vents is at the end of the mains after the last radiator lateral. It's just that I'm a bit surprised that that much steam got into the dry return as one would think that the air in the dry return would prevent the steam from migrating very far. If the dry return drops down and ends (becomes the "wet return") in water and there are no openings in the pipe, the air shouldn't be able to escape. (That's why I was asking if the main vents were at the end of the dry return)  Having steam get into the dry return might mean an air leak. However, the other hand, if there was a major leak, the system wouldn't build pressure .  I think if you lower you cutoff pressure a bit you should be okay with your low boiler water situation. If you have further problems you might want to consider adding a reservoir to your boiler to provide some extra water capacity

    - Rod
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