ongoing steam boiler overfilling problem!

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Old 12-12-10, 01:14 PM
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ongoing steam boiler overfilling problem!

My wife and I have run a small private school for 20 years now out of an old mansion style building using the first and second floors of approximately 4,000 sq.ft. of floor space. The building has a Weil-McClain gas-fired boiler, (1972, Model # LG-7), which has had an ongoing problem with overfilling for the past number of years.

For the approximately first ten years we've been in the building the boiler system had been working fine, serviced each year with one particular boiler service man who now no longer lives in the area. Since he moved away over the course of 6-7 years afterwards the overfilling problem with the boiler gradually developed.

I've been trying to find a solution ever since having had 2-3 seperate plumbing companies working to try and help fix it but with no consistent success as of yet. From all that they've found and done with it, it seems the problem has to do with possibly 3-4 separate or combined issues!?

1) Since the system is almost 40 years old and the pipes are for the most part the same age, slow return-lines seem to be part of the problem, (water in the site glass does rise after ~ 5 minutes when the boiler shuts down and stops heating after a long heating cycle), however a number of the more badly corroded return lines have been replaced, (one section just this Fall), and they've been flushed out a couple of times over the past number of years, so I don't know how much more we can do here!?

2) Surging - A number of times the Service repair people have added chemicals to stop the surging of the boiler water which has seemed to help although it never has fully fixed the problem.

However, after this last section of return-line was replaced this Fall, though the water looks clear in the site glass, it does move up and down quite a bit when the boiler is heating and it also comes out of the LWCO valve pretty dirty before clearing each time I've drained water from the boiler. So I'm thinking that it may need to be recharged with some surge treatment again!?

3) Pressure Gauge/Valve settings - The plumber who's been working with me the last couple of years on it told me a fellow plumber with boiler experience told him that the pressure settings, ('Pressurtrol gauge') were set too high, (originally ~ 5 psi main & 2psi differential-subtractive), and that it should be no higher than 3 psi cut-out/off with the differential ~ 1-1.5 psi. When I lowered them to this it originally seemed to help but now this winter having had an early cold spell and a number of cold weeks, the overfilling problem is as bad as ever! So I'm wondering whether these settings are actually correct or not!?

4) Last but not least, though I've mentioned this to all of the plumbers who've worked on it and they don't seem to think it is part of the problem, to me it doesn't fully make sense why it isn't. This has to do with when the water level starts where it should, ~ 1/3 in. from the bottom of the site glass - it's proper 'set-point', after a cold night and a good long heating cycle through the next morning, by the time the building temperature is up and the boiler shuts off and cools down the water will overfill to over the top of the site glass. When the boiler re-fires throughout the course of a cold day, the Auto-Water feed valve, (McDonnell No. 2 & 47), now comes on not at it's normal 'set-point', (at the bottom 1/3 inch of the site glass), but simply when the water level lowers to the top of the site glass, it's new and much higher 'set-point'! With this new higher refill 'set-point', together with the slow returns and any other possible complicating factors, it only works on overfilling the boiler even more such that during many days of cold weather if I don't constantly drain it at the end of each day, the water would most likely end up in the steam pipes and the building radiators themselves! So I'm wondering whether there could be a problem with the water feed valve in changing it's 'set point' which seems to be only compounding the overfilling problem!

If anyone can help me get somewhat straight on all of this such that we could ever get back to close to the normal operation of this steam boiler system we had for the first decade or so, that would be most greatly appreciated!
Thank You,
Mike Glynn
 

Last edited by NJT; 12-12-10 at 01:45 PM. Reason: 'white space' is good.
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Old 12-12-10, 01:53 PM
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Me no steam head, but I will say that the pressure settings are more correct at the lower ones you are now using, and that they have no bearing on the overfilling issue.

It would seem to me that the problem is with the water feed valve and should be easy enough to fix... but, you also said there is a problem with slow returns which will of course complicate matters... still, the feed valve shouldn't be changing it's 'setpoint'.

Has the boiler been 'skimmed' after each round of replacing pipes? The oil on those pipes is a problem when it floats on the surface of the water in the boiler and will definitely add to any surging problems you are experiencing.
 
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Old 12-12-10, 01:57 PM
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The plumber who's been working with me the last couple of years on it told me a fellow plumber with boiler experience
If your guy doesn't have the experience, why not get HIS guy over there?
 
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Old 12-12-10, 02:09 PM
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I don't even know where to begin so I'm going to come back to this later. I will state now that improper maintenance and operation is the root cause of your problems.
 
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Old 12-12-10, 11:59 PM
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First a little background so you know I'm not just blowing smoke at you. I spent more than thirty years in the design, installation and operation of commercial and industrial steam plants. I like high pressure industrial steam but I detest residential steam heating system for several reasons.

One of the reasons why I dislike residential steam heat is that it requires a "hands-on" attitude from the homeowner. Unlike hot water heating systems that can basically be ignored for years and still function the steam system requires the homeowner to inspect and adjust on a frequent basis, often weekly and daily is not too often. Few homeowners have ever been given the procedures or reasons why these frequent operations MUST be done. There are few heating professionals that really understand residential steam and often as not those that claim expertise are often wrong.

There ARE some good books on residential steam heating but you won't find them in your local library or bookstore. One of the best introductory books is We Got Steam Heat! - A Homeowner's Guide to Peaceful Coexistence by Dan Holohan. Mr. Holohan is one of the world's foremost experts on residential steam heat and he wrote this book for the layman. I strongly suggest that you purchase this book. Mr. Holohan has written other books concerning residential steam heat and you might want to purchase them after reading this one.

First things first. You should NEVER rely on an automatic water feeder to maintain the proper operational water level in the boiler but only to prevent a low water condition. While all steam systems lose a bit of water during normal operation it should not be necessary to add water more than once a week at the worst. I personally think that ALL steam boilers should have a water meter on the make-up water supply and that the meter readings should be recorded at least weekly to see if there is any increase in the amount of water used by the system.

Water returning slowly to the boiler is usually more a problem of faulty air vents than corroded piping although poorly suspended piping may be a contributing factor. Dirt, rust and scale accumulation in the boiler proper where the return piping connects below the water level CAN be a serious problem. Steam boilers MUST be "blown down" periodically to remove the dirt that is entrained (suspended solids) with the make-up water. The frequency and quantity of water blown down is directly related to the quality of the incoming water and how much water is added. A good, tight system with high quality water may only need a short blow down once every couple of months but a leaky system that uses a lot of water or has poor quality water may need to be blown down twice a month or in really adverse conditions even more often. Failure to blow down WILL decrease the life of the boiler.

Ideally, the boiler should be blown down no more than dropping the water level in the sight (not site) glass by a couple of inches and never lower than the bottom of the glass. You should blow down ONLY when the burner has just stopped firing as you want the most pressure but also want the boiler water to be still and allow the settlement of suspended solids as much as possible. A second reason to blow down is to reduce the amount of dissolved solids. These are mostly soluble minerals in the incoming water that are concentrated by the loss of water under normal operation. These minerals, chiefly calcium, will come out of solution and bake onto the hot parts of the boiler and that will reduce the heat transfer (lower efficiency) and also cause the metal on the fireside to overheat if allowed to build up to any significant degree.

When parts are replace they need to be cleaned of all cutting and threading oil BEFORE being installed. Oil will destroy a boiler quicker than almost anything because it adheres to the hot metal parts and insulated them from the cooling effect of the contained water. Oil also is the major cause of "surging" and "carryover" (of water to the steam piping) because it floats on top of the water inhibiting the free release of the steam bubbles as they are generated. Trooper mentioned "skimming" to remove oil but the better plan is to never allow oil in the boiler to begin with. Adding "chemicals" to the boiler to reduce or eliminate surging is the same as closing the barn door after the horse has escaped. If you DO get oil in the boiler you may need to "boil out" the boiler by using chemicals to break down the oil and then blowing out ALL the water along with the oil and chemical. It may be necessary to do this several times to remove all the oil.

Water in the sight glass will ALWAYS be clear on a boiler that has been steaming for a fairly short time period. The reason why is that the water in the glass is condensed from the steam generated by the operation of the boiler, the steam entering the top connection and condensing which pushes the water down and back into the boiler through the bottom connection. In all but residential steam boilers there is a blow down (drain) valve on the bottom connection and when opened it blows out steam and water from both connections and when closed the glass refills with boiler water. Generally a clear glass after being blown down will show anywhere from a slightly "dirty" looking water to almost pure mud; the latter of course signifying a boiler that has been neglected far too long.

It is completely normal for the water in the sight glass to "bounce" a little bit while the boiler is steaming. This bounce could be as little as a half-inch to maybe an inch or more depending on several variables. An absolutely steady level when the boiler is actively steaming is a classic symptom of sight glass connections severely restricted and must be dealt with as soon as possible.

Low water cut outs also need periodic blow downs and as with the boiler proper it depends on the quality and amount of water supplied. It is acceptable for the water to be a dark color as long as it is relatively clear. Mud MUST be eliminated. LWCOs need to be periodically tested to ensure their proper operation.

For single pipe residential steam systems the pressure should be as low as possible. Most such systems work well with no more than 1/2 psi of pressure and very few require more than 1-1/2 psi. If you have a two-pipe system you may need a higher pressure but rarely more than 2 to 3 psi maximum.

Now as far as your original question concerning the ever rising water level I think that the most obvious problem would be a leaking valve in the make-up water supply and the most likely would be the automatic water feeder. Turn off the water supply and see what happens AFTER testing the LWCO.

Post back if you have more questions.
 
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