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Steam boiler water level sight glass schemaitc (C) InspectApedia Steam Boiler Flooding Causes & Repairs

  • STEAM BOILER FLOODING REPAIR - CONTENTS: how the automatic water feed valve works on a steam boiler; how often to manually add water to a steam boiler, What system pressure settings are needed for hot water heat.
  • POST a QUESTION or READ FAQs diagnosis of causes of steam boiler over-filling or water feed valves that don't shut off.
  • REFERENCES
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What causes flooding in steam boilers - why is the steam boiler water level too high?

Here we explain the various causes of excessive water levels in a steam heating boiler.

Keeping the proper amount of water in a steam boiler is a critical function for both safety and to avoid damaging the boiler itself.



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Steam Boiler Water Level Flooding: Causes & Remedies

Steam boiler sight glassDefinition of steam boiler flooding:

Water level inside the steam heating boiler is above the manufacturer's recommended level. A flooded steam boiler will have trouble sending steam up into the building's heating system, resulting in poor heat or no-heat complaints.

The sketch at page top shows how to read the sight glass on a steam boiler. If water level in the sight glass is above or below the recommended level the system needs attention. [Click to enlarge any image]

Our photo shows a typical steam boiler sight glass - a key place to look when checking that the steam boiler water level is set properly. More information about using the sight glass to maintain steam boiler water levels is included in the boiler sight glass article link given just below.

Question: Causes of high water in the sight glass or causes of flooding in steam boilers?

2017/04/23 Anonymous-2 said:

What causes high water level readings in the site glass.

This question was posted originally at SIGHT GLASS, STEAM BOILER

2017/04/18 Anonyous-2 said

I've had a boiler for seventeen years with no problem. When the water in the sight glass goes below a certain level, there's an auto shutoff mechanism that is triggered and a red light goes on. I just fill it until the light goes off and alls well.

McDonnell & Miller Probe type LWCO  PS-801 (C) InspectApedia.comRecently I took the sight glass off [of my steam boiler] to clean it No problems for a few weeks, but now the safety/red light is being triggered by it being over the sight line. Never had that problem before. Drained it and and refilled to proper level and hit reset/on off switch for the shutoff and it light went out, but this morning the water level was above the shutoff level but shutoff triggered/red light on.

The boiler low water cutoff or LWCO is a McDonnell unit. It says McDonnell & Miller ITT. Serial no at top PS-801-24

Any ideas? Thanks for any input. - 2017/04/18 by private email to editor

Reply: Here are the Causes of Flooding in a Steam Boiler

It is not likely that simply removing, cleaning, and replacing the sight glass would itself cause abnormally high (or low) water levels in a steam boiler.

High water readings in the sight glass of a steam boiler, also referred to by the pros as a flooded steam boiler are most-likely caused by one of the following, of which surging is perhaps the most common problem.

  1. Surging in the steam boiler, that in turn cycles the water feed valve when it shouldn't. Surging in a steam boiler, in turn, may be caused by over-firing (burner set too high or wrong burner capacity installed), dirt or debris in the boiler and its water, excessively high steam boiler water pH, or finally an improperly-sized or piped Hartford loop (see HARTFORD LOOP for more detail).

    Clean the boiler and adjust its pH if needed. Too-high pH in boiler water (water that is alkaline or "basic") causes frothing and surging. pH in a steam boiler should be between pH 7 and pH 9.
  2. A leak in a tankless coil used to make domestic hot water (not found on all steam boilers) will leak higher pressure (building water supply pressure) water into the boiler. Try turning off the water into the tankless coil and watch boiler water level over a day or so.
  3. Over-filling the steam boiler manually by a maintenance person - watch out, too-rapid manual filling a hot steam boiler can crack a section. A leaky manual water feed valve (or leaky bypass valve where an automatic water feeder is installed) on a steam boiler can also cause flooding.
  4. Delay in returning condensate to the boiler, possibly due to a condensate return line clog, so that the automatic water feeder has already added water when more condensate returns to the boiler. A check valve on the condensate return line may stick or may be partly debris-clogged, causing both delays in condensate return (doesn't open early enough).
  5. An clogged, improperly adjusted or poorly maintained automatic water feeder valve, or more often, an automatic water feeder valve that's leaking at a valve seat.

    Clogging from rust, debris or scale in the water feeder line between feeder and boiler can also cause boiler flooding by preventing a float-type water feeder valve from opening and closing cleanly. McDonnell & Miller describe a BROKEN UNION TEST [PDF] at the water feeder that can detect this problem. [Click to enlarge any image]
Broken union test by McDonnell & Miler at InspectApedia.com
  1. Motorized steam valves (depending on other boiler condensate return piping system components & design) can cause boiler flooding. The steam valve closes, cutting off steam pressure that would have pushed more condensate into the boiler through the condensate return piping;

    Next the automagic water feeder puts makeup water into the steam boiler.

    Finally, when on a next heating cycle the motorized steam valve opens the pressure returns and more condensate is pushed into the boiler, flooding it.

    For readers unfamiliar with motorizes steam valves we quote this example from Heat-Timer's information on motorized steam valves:

    The MPC Platinum control Series is designed to operate a steam boiler or a steam valve to provide steam outdoor reset. Utilizing the steam cycle concept and the outdoor temperature, the control varies the duration of the steam supply to the building in a cycle based on the outdoor temperature.

    Each of these options has a set of pre-configured, but adjustable settings to meet the specific needs of each building. - retrieved 2017/04/23 (my dad's birthday), original source: www.heat-timer.com/motorized-controls/ Heat-Timer Corporation 20 New Dutch Lane, Fairfield, NJ 07004 USA, Phone: 973 575 4004
  2. Steam push in narrow boiler sections: thanks to Dr. Steam, Dan Holohan (in various texts) for the following more technical example of a boiler design that can cause boiler flooding:

    A boiler with narrow sections, when heated, may suffer what I [DF] call "steam push" - rising bubbles in the boiling water "push" water level in the boiler higher than the water level shown in the sight glass (that doesn't contain an equalizing steam pressure).

    At the end of a heat-on cycle when pressure in the boiler drops and bubbles are no longer pushing water up in the narrow boiler sections, water in the sight glass falls back into the boiler, raising its water level. In my less-expert opinion this doesn't seem likely to introduce a big volume of water but over many cycles it may indeed have an effect.

    This is probably an extension of steam boiler flooding due to over-firing.
  3. A damaged or failing Low Water Cutoff or LWCO control or valve a damaged or clogged LWCO can cause over-filling of the steam boiler if it is not properly-sensing the boiler water-level.

    In discussing abnormal water levels in the steam boiler sight glass in the question by Anonymous-2 above, the homeowner was describing a McDonnell-Miller PS801 / PS-802 type Low Water Cutoff Valve. This is an electrionic water level sensor that uses a probe inserted into the boiler rather than a float-type mechanical water level sensor.

    The fact that a LWCO is a probe-type that doesn't have a moving float assembly should be a tipoff to an electrical or electronic component or probe failure if the steam boiler is flooding.
    Reader followup from Anonymous-2 said:

    I thought I'd let you know what it turned out to be: a relay to the low water cut off probe. Replaced the whole LWCO box & its working like a champ.

Below: an image of some of the interior electrical components of the McDonnell & Miller 801 series LWCO control provided by the reader.

Interior view of McDonnell & Miller LWCO 801 series probe type cutoff control (C) InspectApedia.com JB

Question: what causes flooding in steam boilers?

STEAM HEATING SYSTEMS & CONTROLS does not say what causes high level of water in the steam boiler. Why your boiler in the few days became over flooded.

Reply: List of causes of flooded steam heating boilers

An inspection by a trained heating tech will surely be more reliable than an online guess sight-unseen, but here are some common causes of steam boiler flooding:

- Failure to adequately flush the LWCO can leave sludge in the system, or even just dirty boiler water can gum up operation of the automatic water feeder so that it is not closing completely when it should.

- Surges in the water line can cause the automatic water feeder to also surge and insert extra water into the boiler; dirty or oily water in the boiler can cause surging. If this is the case the boiler needs cleaning.

- High pH in your water supply can cause foaming and water feeder troubles; but if your boiler flooding problem is an new trouble on an old system I tend not to suspect this cause - unless your water system source has also recently changed; If you see foamy water in the sight glass this could be the problem.

- Tankless coil leaks - some steam boilers and many hydronic boilers make domestic hot water with a tankless coil. If the coil itself is leaking, because house water pressure (inside the coil) is higher than boiler water pressure, the leak will flood the boiler. If you have a tankless coil on your steam boiler you might diagnose this by turning off water into the tankless coil and observing if the boiler flooding stops.

- A gravity condensate return with motorized heating zone valves: this explanation is a bit technical, but basically, the operation of the zone valve can interrupt condensate return causing the automatic water feeder to send more water into the boiler.

- Steam boiler running too hot: for example if the oil burner nozzle was changed to a higher gph rate the boiler may be over fired, causing steam to leave the boiler too rapidly for the condensate return rate - I see this as a different type of surge that causes the water feeder to send water into the boiler; then as the condensate later returns the boiler is flooded

- B&G CounterPoint from September 1996. B&G is a producer of heating system control

- Automatic water feeder bypass valve leak: if your automatic water feeder has a manual bypass loop and valve that valve might be open or leaky.

- B&G and some other manufacturers point out that on occasion someone else is adding water to the boiler - improperly - causing boiler flooding

- Steam boiler piping not properly sized or installed around the boiler - but if this is the cause of boiler flooding you'd see this problem probably from day one of the installation.

- Automatic water feeder not properly installed - e.g. too high on the boiler - but if this is the problem you'd get flooding from day one of the installation.

Question: steam boiler keeps flooding - high water in the sight glass

(Apr 1, 2013) Luis said:
I have a gas boiler which continues to overflow. The sight glass floods even some pipes that run through the floor and o up the wall with a steam trap a gauges at the to of the pipes. I called a company but they have not been able to find the problem.

Reply:

Luis if the steam boiler keeps overflowing, or flooding, most likely the water feeder is out of order.

On 2017-02-18 by (mod) - do not use an electronic water feeder with a McDonnell Douglas Series 800 LWCO manual-reset

Sam, that's a good question.

McDonnell Douglas says that using an electronic automagic water feeder with a McDonnell Douglas Series 800 LWCO manual-reset model can lead to flooding of the steam boiler - that is, the water feeder may over-fill the boiler.

See this ITT McDonnell Miller LWCO manual for details

https://InspectAPedia.com/heat/ITT-McDonnell-Miller-PS-802-852-Water-LWCO-Manual.pdf

On 2017-02-18 04:56:59.317174 by Sam

I just bought a McDonnell Douglas series 800 probe low water cut off manual reset model and it says do not use with electronic automatic water feeder's do you know why

On 2017-01-21 by (mod) - failure to flush the low water cutoff is unsafe

Gene,

Failure to flush the low water cutoff might let so much sludge build in the boiler that the water feeder and LWCO are both jamming - and unsafe. That's the issue to which your plumber refers.

It might be necessary to drain and clean the system as part of repair.

We love your questions and are glad to try to help but next time please don't SHOUT

On 2017-01-21 17:38:27.926507 by GENE - I never touch our steam boiler water feeder system; it flooded the room

What prevents too much water from going into boiler? I have automatic water feed.

I never touch it. Too much water showing in glass has happened twice.

Water from radiator Flooded first floor living room. New furnace in dec 2014. Flooded room in aug 2015 and too much Water in glass jan 2017.

Plumber said dirt on sensor in 2017. 1st time he replaced automatic feed.

Thanks
Panel(?).

Question: water feeder is flooding steam radiator

Two weeks ago I found water flowing out of my steam radiator vent overnight. We drain and flush water out of the boiler and fill up the boiler. The automatic water feeder seem to be working properly, it stop feeding water at the 40% of the sight glass and the water level stay the same for about 24hrs,suddenly it was overfill again overnight and the system is not operate through the whole time.

My system has separate McDonnell and Miller automatic water feeder and Low water cut off. We don’t know what cause the overfill overnight, please help. - L.S. 7/14/2013

Reply:

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website.

That said, I can GUESS that the automatic fill valve may be working improperly, sometimes sticking "on" or in the "fill" position. This can happen due to debris inside the control or in some units even from a loose wire. There could also be a problem at a pressure-reducing valve ahead of the boiler. Try flushing out the low water cutoff thoroughly several times.

That will cycle the water-feeder - fill valve repeatedly as well. If the valve continues to overfill the boiler I'd ask for a service call to have the valve checked, repaired, or replaced. I suppose there could be another problem outside of the fill valve - here are more things to check:

If the condensate return system is blocked condensate may accumulate in and flood an individual steam radiator (ultimately meaning loss of heat), or such problems may occur on all radiators on an individual condensate return piping system that is blocked downstream from the radiators.

If your radiators are flooding as you describe and the heat is OFF then it's not a condensate return blockage problem it's a water feed problem.

Question: steam boiler keeps over-filling, my low water cutoff switch has no flush valve

Two weeks ago I found water flowing out of my steam radiator vent overnight. We drain and flush water out of the boiler and fill up the boiler. The automatic water feeder seem to be working properly, it stop feeding water at the 40% of the sight glass and the water level stay the same for about 24hrs,suddenly it was overfill again overnight and the system is not operate through the whole time.

My system has separate McDonnell and Miller automatic water feeder and Low water cut off. We don’t know what cause the overfill overnight, please help. L.S. 7/14/2013

Reply: flush the LWCO low water cutoff valve & check its operation

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website.

That said, I can GUESS that the automatic fill valve may be working improperly, sometimes sticking "on" or in the "fill" position. This can happen due to debris inside the control or in some units even from a loose wire. There could also be a problem at a pressure-reducing valve ahead of the boiler. Try flushing out the low water cutoff thoroughly several times. That will cycle the water-feeder - fill valve repeatedly as well. If the valve continues to overfill the boiler I'd ask for a service call to have the valve checked, repaired, or replaced. I suppose there could be another problem outside of the fill valve - here are more things to check:

If the condensate return system is blocked condensate may accumulate in and flood an individual steam radiator (ultimately meaning loss of heat), or such problems may occur on all radiators on an individual condensate return piping system that is blocked downstream from the radiators.

If your radiators are flooding as you describe and the heat is OFF then it's not a condensate return blockage problem it's a water feed problem.

As it will be helpful to other readers, and as its publication may prompt other readers to offer a helpful suggestion, I will include a redacted (to respect your privacy) version of this discussion online in our article [found just above on this page].;

Please keep me posted on how things progress, and send along photos if you can. Such added details can help us understand what's happening and often permit some useful further comment. What we both learn may help me help someone else.

Reader follow-up:

I sent the picture to one of the plumber,he said that my LWCO dose not have any drain to flush water. I attach the picture of the LWCO for your reference.You could post my name as Ling Sok in Lowell and I'll keep your team update. L.

Reply: look for a leaky tankless coil or a defective water feed valve

If a steam boiler uses a low water cutoff that does not need flushing (and there are such devices) the device is normally designed and installed to be protected from sediment, or uses a technology that is not affected by sediment in the boiler or its piping.

Nevertheless, if your boiler is over-filling it seems likely to me that the problem would be checked for first by a careful look at the feed valve and its sensors.

A second source that you might need to check is the hybrid case of a steam boiler that also includes a tankless coil for making domestic hot water. In that case, if the coil itself has developed a leak, it will leak building water out of the coil into the boiler interior, raising the boiler pressure and water level improperly.

Question: steam boiler over-fills

(Feb 18, 2014) Nikke said:

The water level on my boiler is filled up to the top and it doesn't seem to come down even though I've been draining out the water. I wonder if there're something wrong with it.

Reply:

Nikke, if your water heater has an automatic water feed valve, as you drain water out the feed valve puts more water in.

If indeed your boiler is a steam system the water level should be about where the indicator mark is on or behind the glass boiler level gauge.

Water also enters a steam boiler as returning condensate. Condensate returns to the bottom of the steam boiler; in a residential system it would be very odd for there to be so much condensate returning that it would over-fill the boiler;

Check that the automatic water feeder is not over-filling, or just close it off temporarily, then drain the boiler to the proper level.

If then on opening the water feed valve the boiler water level is too high you figure the problem is the feeder valve.

Finally (well not really as there could be some other problem I can't guess from just your note), so sort of finally, if your steam boiler also includes a tankless coil that makes domestic hot water and if that coil is leaking it could leak into the boiler, over-filling it. If this is a possibility on your system search InspectApedia for "Tankless Coil Leaks"

Question: Utica steam boiler over fills

(Nov 6, 2014) Will said:

I have an older Utica Boiler & I was draining water from the blow down valve because the sight glass was filled up. I had to drain 4 5 gallon buckets until I could see the level drop to where it's supposed to be. The next day it filled right back up again & I had to drain about another 20 gallons out.

Now it's everyday & unless I shut the water off from the main before I go to work, it fills up again and the radiators in my bedroom & bathroom start leaking until I drain it all out. I replaced the Low Water Control, flushed out the ball & even replaced the blow down valve & the same thing occurs daily. Other than shutting off the main there really isn't anything to stop this from happening. What am I missing?

Reply:

Will,

Sounds as if your automatic water feed valve is not working properly.

The low water cutoff or LWCO may on your system be completely separate from an automatic water feeder.

Other sources of high water pressure in a boiler can stem from a bad pressure reducing valve or from a boiler containing a leaky tankless coil.

Will said:

What are the signs if the tankless coil is leaking? In other words, what do I look for? Is there a tell tale sign? The boiler doesn't seem to be leaking outside the system.

Reply:

Will

If a tankless coil is leaking internally, that is there are no visible leaks on the outside of the boiler where the coil is mounted, look for abnormal increases in the boiler's water pressure or a dripping or leaking pressure relief valve on the boiler.

See TANKKLESS COIL LEAKS

Question: McDonnell No 101-A buzzing water feeder or other 101-A Water Feeder Troubles

(Jan 4, 2016) Anonymous said:

My McDonnell No 101-A water feeder for my oil heat boiler is buzzing and will not stop. The heat is steam heat for the house. Any ideas and how to stop the buzzing?

(Jan 27, 2016) MikeF said:

I have a McDonnell 101-A water feeder on my steam boiler. Recently began having problems with over-filling. I shut off the auto feeder shutoff valve to verify that the manual water feed valve we not leaking, and determined it was not. Before this test period, at one point the glass water level gauge showed normal water level, about two thirds up the gauge.

However, the two overfill release valves high above the boiler had a steady stream of water shooting straight up a few inches above the valve.

I manually dumped water out of the boiler and the boiler and this soon stopped the release from these valves. After the test for the manual valve leaking, I opened the auto feeder valve and monitored the system. All was fine until this morning. At 6:00 AM the boiler was running fine and the water level was normal.

Three hours later the boiler was off, but the water level was higher than the glass water level gauge could show. No water coming from release valves. Again manually dumped water from the system to get to normal level.

System operating normally today since then. So it seems the auto feeder intermittently over fills the boiler. Is the valve bad? Would cleaning the strainer help? Any suggestions? Thank you for any help.

Reply:

Anonymous:

I think I would shut the unit off, in hopes of avoiding more damage, call for repair, and check and monitor the water level in the boiler, adding manually if needed.

But first try flushing out the low water cutoff valve.

We discuss buzzing electrical relays at HVAC NOISE group 1 - banging, bearings, BUZZING

Bad relay control switch or contactor relay: Bad or failing ... relay switch or bad ... contactor relay switch may buzz or hum. These are usually low-voltage (e.g. 24VAC) controls that are used to switch on the higher-voltage-operated motors [or devices]

And beginning at STEAM BOILER FLOODING REPAIR we explain the causes of excessive water level in a steam boiler.

Question: boiler uses manual feed, boiler keeps taking on water when the valve is closed

(Jan 11, 2016) Michael said:
I have a manual feed system. but the recently the boiler continues to take on water even when the manual shut off valve is shut. Do I need to replace the shutoff valve?

Reply:

Check for a clogged, delayed return of condensate first: that can lead to overfilling the boiler.

Question: Automatic water feeder, keeps feeding boiler, boiler now flooded

(May 2, 2016) Jose Huertas said:

Auto feeder keeps running every 5 minutes boiler flooded and now wont start but keeps filling. What to do Help

Reply:

I'd shut off the boiler first, also the water feeder if it's power is separate. It sounds as if its control or float on the water feeder is not working. You'll need repair from your heating service tech.

Steam Boiler Water Feeder & LWCO Manuals & Steam Boiler Flooding References & Research

...


Continue reading at WATER FEEDER VALVE, STEAM or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see HARTFORD LOOP

Or see STEAM BOILER SIGHT GLASS - how to read the steam boiler water level

Or see WATER FEEDER VALVE, STEAM FAQs for more diagnosis and repair help with water feed valves on steam boilers

Or see WATER FEEDER VALVE, VXT-24 FAQs if your water feeder is a Hydrolevel VXT-24 programmable water feed valve

Or see STEAM HEATING SYSTEMS & CONTROLS - home

Or see WATER FEEDER VALVE, HYDRONIC BOILER

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