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Here we explain the various types of manual and automatic water feeder valves used on steam heating boilers, including when and how to add makeup water to a boiler.

If your heating system is hot water, not steam, see Water Feeder Valves, Hydronic Boiler. If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES. If your heating system is not working properly, see NO HEAT - BOILER / FURNACE DIAGNOSIS.. This website answers nearly all questions about central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

The photo above shows a modern automatic pressure-reducing water feeder valve on a hydronic (hot water) heating boiler - one of the safety controls which we discuss in this article. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Steam Boiler Water Feeder Valves, Automatic & Manual

Keeping the proper amount of water in a steam boiler is a critical function for both safety and to avoid damaging the boiler itself. So on a steam boiler we consider the automatic water feeder to serve as a safety device too. Water feed valves on steam heat systems operate under very different requirements than those on hot water (hydronic) heating systems.

Residential steam heating systems are mostly "low pressure" systems operating at less than 2 psi. In fact if you see the pressure set higher on a residential system it is often an indicator that the occupants/technician have been having trouble getting the steam heat to locations where it's needed.

But steam heat systems all consume some water which escapes from radiator air vents during the time that the steam (heat) is first rising in the building. So unlike a hydronic water feeder, the steam boiler water feeder is going to be much busier, regularly adding makeup water to the steam boiler, but operating at low water pressures.

Automatic water feeder valves on steam boilers

Automatic water feed valves on steam boilers (such as the McDonnell & Miller automatic water feeder shown at left) perform functions similar to the valve described earlier for hot water boilers.

But because the steam boiler will be damaged or unsafe if its water level falls too low and because it's normal for a steam system to use (lose) water, the water feed valve on a steam boiler has to operate more often, and will be a more heavy-duty (and probably reliable) device.

The black box shown in our photo at left is a Mcdonnell & Miller™ automatic water feed valve. On a signal (normally from the low water cutoff valve) the water feed valve will open to send additional makeup water into the steam boiler.

Manual water feeder valves on steam boilers

In our photo at left, a close up of our page-top photo, you can see a "manual water feed" button on the top of the automatic water feed valve.

This button permits overriding the automatic feature of the valve to force water into the steam boiler.

But on lots of steam boilers, especially older residential units, you may find that only a manual feeder valve is installed. You'll need to use it to manually add water to the steam boiler whenever its water level is low. Below we discuss the detailed procedure for manually adding water to a steam boiler.

In our photo above at automatic water feed valves, an automatic water feeder is installed. But the yellow valve handle is an manual water feeder that will bypass the automatic water feeder and force water into the boiler. On this particular system you shouldn't need to use the manual feeder lever unless the automatic feed valve is broken.

As you'll see in that photo, the yellow handle is in the horizontal position, "across" the water pipe, showing that it is in the "closed" position (we're depending on the automatic feed valve).

How often you'll need to manually add water to a steam boiler that lacks an automatic feeder depends on how rapidly your particular steam heating system loses water. If you are new to your particular steam heat system, you should check it's water level (and flush the low water cutoff valve) at least weekly until you know more accurately how the heating system behaves in normal use.

Steam heating systems without an automatic water feeder are less safe and risk serious boiler damage should boiler water be lost and should there be no low water cutoff installed on the system. That's why all modern steam heating boilers can be expected to include at least a low water cutoff valve. Low water cutoff valves are discussed in detail at Low Water Cutoff Valves, Boilers.

When, How, & How Much Water to Add to a Steam Boiler

If your steam boiler has an automatic water feeder you should see the water level always close to the fill-mark and the automatic water makeup valve will normally do this job for you.

When to add water to the steam boiler

If your steam boiler has only a manual valve for adding water, until you know the system's rate of water usage, you should check the water level at least once a week during the heating season.

You'll want to add water whenever the sight glass shows that the water level has dropped to the "add" mark and you should always see some water in the sight glass.

How much water to add to the steam boiler

The sight glass on a steam boiler, combined with a mark or gauge usually placed on the sight glass or on the boiler body behind the glass, will show the proper level to which the steam boiler should be re-filled when it's low on water.

See Sight Glass, Steam Boiler for details of this component.

Frequently Asked Questions (FAQs) about automatic or manual water feed valves used on steam boilers

Question: what causes flooding in steam boilers?

It does not say, what causes high level of water in the steam boiler. Why your boiler in the few days became overfloded.

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: how does the automatic water feeder add makeup water to a steam boiler

Does the automatic water feeder on the steam boiler add water slowly to the boiler and if you have to add water manually should you add slowly when the boiler is not running. - Mary Jo Barranco

Reply:

Mary Jo:

If your steam boiler has an automatic water feeder it will add water whenever the level drops enough to drop the float in the sensor. It doesn't feed water continuously. The water feeder will add water frequently enough, and in small enough doses, and at a slow enough rate that even if the boiler is hot the makeup water won't damage the equipment.

You can take a look at the water level in the boiler by noting the sight gauge - that vertical glass tube. There may already be a normal water level mark - if not, just put one on with a magic marker. If you should see the water level in the boiler fall say half way between that mark and the bottom of the sight glass, then I suspect the auto water feeder isn't. Otherwise it should come on by itself and restore water to the boiler as needed.

Question: how to diagnose frequent on-cycling of automatic water feeder on boiler; initial dwell? dip switch settings?

My new steam boiler has an auto feeder that cycles on frequently, even when the boiler has been off for hours, such as overnight. Is that normal? I am considering changing the DIP switches to change the dwell/feed but need your advice. Can you tell me if increasing the feed time would add more time between cycles? What does "initial dwell" refer to? There is no marker on the sight glass but the water generally lays at one third the twelve inch glass. I think that is low but even if I add water manually, that level is maintained after a while. - Bob Q from Brooklyn

Reply: look for a leak in the steam piping, particularly the condensate piping, or possibly improperly functioning steam vents

Bob Q,

When a steam boiler is and has been cold for a while no water should be leaving the boiler, and therefore I wouldn't expect the auto water feeder to cycle on. Even though your steam boiler is new, it's likely that your steam piping, condensate return lines, etc. are not. I'd look for a leak around the boiler itself. You can miss a small boiler piping leak when the pipes are hot because the leaking water just evaporates. Check carefully when the system has been cold and off for a few hours or more.

I understand the temptation to adjust the automatic water feeder, but those adjustments wouldn't be expected to make the device feed water when the system has been off and cold.

When you feed extra water to the boiler it will eventually be consumed (steam losses in the system - all steam systems consume some water) and since you fed it manually, the system will naturally return to the water level being maintained by the automatic water feeder.

About whether or not the set level of water is too low, look on the boiler itself - many of them have a "water level" line marked or riveted on the boiler side by the manufacturer.

If you send me (use the CONTACT link on our pages) the brand and model of your water feeder I'll dig up the instructions to see what further advice we can offer.

Reader follow-up about frequent cycling of water feeder: found leaky steam piping in hidden condensate return line

You advice on looking for a leak in the return lead me to a length of pipe that looked like swiss cheese on close inspection. The system is over 100 years old and the old return in the basement behind a wall was leaking where I couldn't see it. I had the pipe replaced with copper and all is well. No more low water cycling. Thank you for your good advice. - Bob Q from Brooklyn

Reply-DF:

Thank you for the follow-up Bob, your report will help other readers who are trying to track down steam boiler water loss problems.

Question: How do I know if I have a 120V Solenoid or 24V Solenoid?

How do I know if I have a 120V Solenoid or 24V Solenoid? - Evan.Penalba

Reply: check device labels, installation instructions, or wire diameters

Evan, take a look at the information labeling on your water feeder or other device: the operating voltage will be shown. If the label has become lost you'll want to take a look at wiring and installation instructions for the device.

If you don't have the installation and wiring manual for the device you (or we for you) can find that information from the manufacturer if you can identify the brand, model, or other information for the water feeder or other device.

Finally, if the device is already installed and wired, just take a look at all of the wires entering the water feeder. 24V electrical wires are typically very small in diameter - typically 18-20 gauge while 120V electrical wiring will be the size of normal building electrical wiring - typically #14 or #12 copper wire. You can see photos and tables of electrical wire sizes and diameters at SE CABLE SIZES vs AMPS.

Question: VXT-24 automatic water feeder from Hydrolevel - how to wire up

just installed a VXT-24 auto water feeder from hydrolevel company in the make up water line on a Pennco steam boiler. it has a mcdonnell LWCO and its a gas fired unit. i'm having trouble getting power to auto feeder. It is a millivolt system. Do i need a transformer? I'm not a wiring or controls guy, can you please help - Dan G

Reply:

Dan:

Yes, the Hydrolevel VXT-24V automatic water feed control for steam boilers is designed to be powered by a 24VA transformer. That wiring detail should be in the installation instructions that came with your unit - if not, I'd check with Hydrolevel and ask for an installation guide. If you can't find the installation guide you can also send us our email (see our CONTACT link at page left) and I'll send you a copy.

WATCH OUT: The particulars of how your control should be wired up depends on your boiler and the control it is replacing. Hydrolevel shows the wiring connections for quite a few control replacements, McDonnell Miller, Honeywell, etc.

Contact Hydrolevel at P.O. Box 1847, New Haven, CT 06508 Tel: (203) 776-0473, or at hydrolevel [dot] com

Reader follow-up:

thanks, the wiring diagram that came with the feeder matches the mcdonnell LWCO. i guess my problem is that i cant find where the power is coming from. the only wires that come into the unit is from the thermostat upstairs. it goes to the honeywell pressure switch, the gas valve, and LWCO. where do i wire the transformer from? thanks for the quick response. - Dan G.

Reply:

Yeah Dan, I should have mentioned that sometimes the low voltage transformer that is powering HVAC controls, thermostats, even doorbells can be hidden away in a closet somewhere, or in a ceiling. Look for an electrical junction box with a small transformer mounted on it. Also look at other controls on your heating systems - some other controls may include a LV transformer that can be used to power more devices.

Start by tracing those physical wires backwards from the LWCO - just keep following them.

Reader follow-up: thank you, you've been a big help. appreciate everything

Question: one pipe steam system, two boilers, Asco solenoid make up water supply troubleshooting

I have a one pipe steam system with two Hydrothermal boilers. The make up water tank has a Watts Boiler Water Level Control Type D132A Model M. It is connected to the water gage and it is the device that triggers the Asco solenoid valve to add fresh water to the condensate tank. I was draining the system as part of the maintenance and knocked the valve and the body with a wrench, and as I suspected some malfunction, I could see an spark inside the electric box that controls the chamber.

The box has two electric wires that are regular electric wires going in and inside there are three cables (multiple tiny hairs of copper-not solid conductor like regular electric wires). One of this cables became loose. The other two cables seem to be connected to one end on a sealed small tube containing the mercury and which acts as a trigger or contact. I managed to connect the cable to one of the other two terminals and it does open the solenoid valve, but it will not close it, then I am connecting it in a permanent open position and have no way to figure the circuit out. I presume it connects with the other two cables to the end of the tube. If that is the case, can it be repaired?

This is an old system, but working perfectly, other than for this aging wiring. If you have a guide on the circuitry or any suggestion, I would appreciate it. Thank you in advance for your time and consideration. Robert.

Reply:

Robert I'm sorry but I don't think I have a clear enough understanding of the condition of your water feed valve - it's a critical part for safe operation of the steam boiler, though you could, of course, shut it down and feed water every day or two manually - not at all convenient. If there is any doubt about the condition of the valve, I'd replace it.

Question: steam boiler water feeder McDowell & MIller won't stop sending water into the boiler [McDonnell?]

i have a problem with my water feeder a mcdowell & miller when it calls for water it sends it but it will not stop do i need a new water feeder??? thanks - Will

Reply:

Will, you might need a new automatic water feeder, but it's an expensive part to buy and install. I'd try flushing the valve thoroughly to see if that clears up the trouble. If that doesn't work, before replacing the valve ask your steam heat service tech if s/he can open and service the valve.

Question: steam boiler using too much water, seems to be leaking somewhere

I have a gas boiler Bryant model 234-55. The problem having is have to fill glass sigh everyday, which was every 4 plus days before.. So I used the manual fill and filled glass sight up full, and beyond, water started running out of boiler, but could not find out from where.. But boiler works and heat, but uses a lot of water. No leaks in pipes or valves on radiators. Hope you can help me, Thanks, - Mike

Reply:

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with the boiler piping, water feeder, condensate return, or other components that might explain the "leak" you report.

That said, here are some things to consider:

• it sounds as if you are describing a steam heating boiler
• it is normal for a steam boiler to consume some water; that's why an automatic water feeder and low water cutoff safety valve are installed on modern units; some older steam boilers still require manual addition of water, every day or three depending on the level of heating system usage
  
  Watch out: DO NOT OVERFILL the steam boiler - doing so can cause several operating problems as well as spilling water out of the relief valve.
  
  A steam boiler will have a "fill-to" line marked on the boiler, generally where you can see it in relation to the water level in the boiler indicated by the sight glass or tube.
• if the quantity of water used by the boiler is unusual or improper (something to ask your trained steam heat service technician), then there may be a condensate return pipe leak, perhaps not in plain view, or perhaps radiator valves that are not closing when hot, but continuing to release steam (water vapor) all during the heating cycle.

Questions & Answers regarding this article

Questions & answers about how and when to use and maintain the water feed valve on steam boilers

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• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

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