Q&A causes of & repairs for flooding in steam boilers - the steam boiler water level too high?

This article series explains the various causes of excessive water levels in a steam heating boiler.

Steam Boiler Water Level Flooding: Causes & Remedies

These questions & answers about over-filling or flooding steam boilers were posted originally at STEAM BOILER FLOODING / SURGING REPAIR - be sure to review the diagnostic information given there.

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

[Click to enlarge any image]

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 2018-08-14 23:38:20.027394 by (mod) -

It's possible that the probe or water sensor needs to be cleaned or replaced.

In the ARTICLE INDEX where I list references see the live link for

Hydrolevel VXT RESIDENTIAL Model VXT-24 Programmable Water Feeder for Steam Boiler, [PDF] Installation, Maintenance, Troubleshooting Instructions" [PDF] Hydrolevel Company, 126 Bailey Road, North Haven, CT 06473 USA Tel: (203) 776-0473

and you'll see the test procedure to use.

On 2018-08-13 17:13:27.844783 by Anthony

I have McDonnell Low Water Out PS-802-24 and Hydrolevel VXT-24 installed in the steam boiler

One time it overflood the boiler and afterward it don't feed water automatically but the control turn off the boiler if water level is low.

Is it possible the probe need to be clean out? Or how to test the probe with electronic multi-meter? I try to unscrew the probe out but no way, any suggestion or use penetrate fluid to get it out

On 2018-06-04 14:48:19.600608 by (mod) -

Joe,

From your comment it sounds as if the pressure relief valve is doing his job and the problem is a cause of Over pressure in the steam boiler. Have you checked the pressure control switch. It could be defective.

Keep in mind that if a relief valve spills repeatedly it can become clogged with mineral deposits and debris which in turn could make the boiler unsafe,.

On 2018-06-04 02:16:21.313230 by Joe

Hi. I have a steam boiler with. Series 47-2 water feed control. The boiler seems to flood. I turned on the boiler drained down the glass until it was in the middle and let the boiler come up to pressure. The boiler relief valve blew off at 10 psi it’s set at 15.

As the boiler cooled down the sight glass flooded. I ran another cycle and valved out the make up and everything seem to work fine other then the relief valve seems to blow off at around 12 psi. Bad #47 control?

The boiler gets blown down every day. It’s been in operation for 5 years. Not sure what I’m missing here. Thanks for your help.

On 2018-01-31 20:39:25.265421 by (mod) -

Here for other readers is an image of the Hydrolevel VXT-24

On 2018-01-31 20:38:53.528437 by (mod) -

Jay,

The McDonnell Miller Water Feeder Series 47-2 (photo below) is almost certainly what you're asking about. That device has served reliably on thousands of boilers for decades provided it is maintained as the manufacturer instructs.

The No. 2 switch is added to provide a LWCO function.

Hydrolevel's VXT-24 is useful in particular when there is a problem with delays in the return of condensate to the boiler as the programmable VXT-24 can be set to wait before permitting makeup water to feed to the boiler.

I very often see the VXT-24 installed in concert with a McDonnell Miller water feeder control. Quoting from our article on that control,

This automagic water feeder is described by the manufacturer as a universal control that can be used with virtuallyt any type of probe or float type low water cutoff control found on steam heating system boilers. The VX24 is programmable: the technician can set the make-up water feed volume, timing, and other features.

The control includes both an under-feed protection to add more water than programmed if necessary and a lock-out to prevent flooding of the steam boiler.

Delaying feeding make-up water to a steam boiler (using the VXT-24) prevents over-filling the steam boiler.

So yes that would be an improvement in the control for your boiler. Excuse the arm-waving warning that you need to confirm the control's installation and use with your boiler manufacturer or service company.

See WATER FEEDER VALVE, STEAM at inspectapedia.com/heat/Steam_Boiler_Water_Feeders.php and also

see Q&A about the VXT-24

at WATER FEEDER VALVE, VXT-24 FAQs at inspectapedia.com/heat/VX-24_Steam_Boiler_Water_Feeder_FAQs.php )

Keep in mind that you reported that the MM 47-2 was over-filling the boiler due to "a fill valve failure". That failure might have been simply due to lack of maintenance: flushing the valve periodically (the yellow handle in my photo) is important.

The instructions for the MM 47-2 and 247-2 are at inspectapedia.com/heat/McDonnell-Miller-Water-Feeder-S47-S247-Instructions.pdf as well as of course in your hands as you've installed a new control.

Readers may also want to see instructions for the LWCO switch that works with the MM 47-2 at inspectapedia.com/heat/McDonnell-Miller-LWCO-Switch-Instructions.pdf

On 2018-01-30 12:07:59.210388 by jay

replaced the M-M 47-2 assembly w/switch because the old one was leaking (overfilling the steam boiler) due to fill valve failure. Should I need to consider additional controls such as VXT-24 to avoid surging and future overfill? Need your expert advise, Thanks

On 2017-04-29 23:47:33.465466 by (mod) -

Yep - we used to work on converted coal boilers - techs added an oil burner, often in the 1950's. Often we'd just cut a hole and fire the burner right through the door.

This example https://inspectapedia.com/heat/57SGrand226-DJFss.jpg shows that I moved the burner up to fire it through the upper door of the old coal-fired heating boiler - discussed at https://inspectapedia.com/heat/Oil_Burners.php

On 2017-04-29 20:55:28.014340 by Philomena

Thanks, again, Dan:
I will wait until someoone with an IPhone can take those pictures. It uses hot water so it is a hot water boiler. It used to be a coal BOILER then, at one time. The coal bin was still here (sans coal) when we moved here in 1967. We called everything a furnace in the "old" days.

We had a wood/coal furnace that heated only one room through a floor grate. (193's-1940s) Heat in kitchen with kerosene - wood-burning stove. No heat in upstairs bedrooms back then .

I'm learning, still.

Thank you!

On 2017-04-29 13:48:45.900801 by (mod) -

Philomena

Indeed, use the page top or bottom CONTACT link to send me photos of your heater as well as close-ups of its data tag and other identifying marks and of its controls, and I may be able to find helpful information, manuals, etc.

Beware that some really smart plumbers were also English majors so they may not communicate precisely nor use words the same as you or I.

A mixing valve mixes cold in with outgoing hot water used for washing and bathing "domestic hot water supply" thus lowering the temperature of hot water coming out of a faucet or shower head - both to avoid scalding burns and to make the hot water seem to last longer.

That's used when there's a tankless coil on the heating boiler that's the source of domestic hot water and also on some other water heating systems when the heater is run very hot.

A water feeder valve is a manual or automatic valve that puts more water into steam boiler when needed. Steam boilers use up a bit of water at every heat-on cycle so makeup water is needed.

See https://inspectapedia.com/heat/Steam_Boiler_Water_Feeders.php for steam boilers,

and for "hot water" (hydronic heat - that is, not steam but hot water in radiators or baseboards) boilers

see https://inspectapedia.com/heat/Water_Feeder_Valves.php

So what you're calling a "furnace" - if it uses steam for heat - I call a steam boiler.
And
if your heat is by hot water in radiators ( not steam ) I call that a hot water or hydronic heating boiler.

I use the term "Furnace" to describe forced hot air heating systems. But I acknowledge that normal people use these terms in a heating equipment word salad.

On 2017-04-29 11:05:49.084305 by Philomena

Thank you so much for your quick reply. I turned the thermostat down to 58 degrees last night and the water level stayed where it belongs.. The problem here is that it is so difficult to find HVAC people who know how to repair these old furnaces.

I had one plumber who asked if he could take a picture of my National.

Most of the older plumbers who worked on these boilers are gone. The younger guys are afraid to touch it, I think and just say I need a new furnace, but it has been very dependable.

He did replace several very rusty parts; including a copper line had a hole in it.with a tiny hole in it.

He worked on it for 6 straight hours and came back the next morning for two hours.. He said my mixing valve needed replacement. Is a water feeder valve the same as a mixing valve? (sorry for question)

I have sent him a snail mail letter and have left a voice mail for him. (He is 78, and retired --45 years' experience.)

When he left, he did tell me to watch the furnace and to call him if anything was amiss. But he felt everything would be ok. He will be back on Monday.

Thanks again, Dan.



Thank you SO much. You're great!

On 2017-04-29 01:52:01.332084 by (mod) -

Sounds as if the water feeder valve is over feeding; Ultimately you'll lose heat. IF you don't need the boiler, yes turn it off. I'd tell the plumber that if he can't find time to come and fix the job that he started, you'll have to hire someone else and collect the cost from him - voluntarily or in small claims court. That might get him going.

On 2017-04-28 22:25:21.426985 by Philomena

First, I am 88. I have a gas fired furnace about my age (or older). It has been working fine UNTIL

i had a Master Plumber come and drain it and to replace some parts. My hot water was scalding and he did something to the "water feeder". Since he came, I have been noticing the water levels rise.

I called him but he is extremely busy. I asked if it was dangerous. Later, I called him again and he was very busy and needed to go on vacation. I told him I would watch the furnace. I have been watching it.

The water level today was close to the top of the sight glass. I took water out and eventually it went to the right mark. Since 9:00 this morning (it is now 6:00) the water has gone up about 1/2 inch and I know it will continue to rise. First, is this dangerous. Should I turn OFF the furnace since it is now warm weather.

I don't understand parts of the furnace or what to do.
Can you please help?
Thank you

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 RELAYS

Also see HEATING SYSTEM BUZZING NOISE

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 / SURGING 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.

...

Continue reading at STEAM BOILER FLOODING / SURGING REPAIR - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Boiler Water Level Articles

• HARTFORD LOOP
• STEAM BOILER FLOODING / SURGING REPAIR
• STEAM BOILER SIGHT GLASS - how to read the steam boiler water level
• STEAM HEATING SYSTEMS & CONTROLS - home
• WATER FEEDER VALVE, STEAM FAQs for more diagnosis and repair help with water feed valves on steam boilers
• WATER FEEDER VALVE, VXT-24 FAQs if your water feeder is a Hydrolevel VXT-24 programmable water feed valve
• WATER FEEDER VALVE, HYDRONIC BOILER
• WATER FEEDER VALVE, STEAM

Suggested citation for this web page

STEAM BOILER FLOODING REPAIR FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to STEAM BOILERS

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