5 Steps to Healthy Steam Radiators

Steam radiator diagram how it works

5 Steps to Healthy Steam Radiators

A simple checklist for solving five common problems with your steam radiator

steam radiators

The simple anatomy of a radiator

* This is from an article written in 2012 (an old print issue of our newsletter. Click here to view it!)

      Every winter, especially when it begins, we receive many calls about the steam radiators acting up.  Residents hear loud clanging, banging, knockinghissing or other strange noises from their heating pipes, feel too much heat or even no heat at all. Sometimes, residents alert us of leaking water or escaping steam from the radiator, leaving the apartment walls or floors wet or feeling damp.

       Someone is always inconvenienced when things go wrong with a radiator, whether it's the resident who needs the radiator repair or her downstairs neighbor, who's become the unwilling recipient of water that has found its way from the radiator into his apartment. 

      The good news is, such problems are often avoidable and sometimes, surprisingly easy to solve. With some vigilance and by abiding some rules-of-thumb, we can usually prevent these issues from happening or at least catch them before they cause unnecessary aggravation or serious damage.

     Let's begin by looking at how a one-pipe steam radiator works.*

How a Steam Radiator Works

Steam radiator diagram how it works

Animation of how a one-pipe steam radiator works.

As shown above, the main parts of a steam radiator consist of two valves, the supply (or "radiator") valve and air (or "vent") valve, and the cast-iron radiator body. 

      When the boiler is triggered and steam is generated, it flows from the boiler by a series of pipes and enters the radiator body through the supply valve. In the above animation, the green arrows represent steam. 

      As the steam fills the radiator body, it pushes out the cool air (blue arrow), which escapes through the air valve. When the air has left and the steam fills the radiator body to capacity, the air valve senses the steam and automatically closes to trap the steam inside. 

      The steam then heats the metal fins on the radiator, which warms the room. 

      Finally, the steam cools down and reverts to water, called condensate (red arrow), and then flows out of the radiator through the supply valve back to the boiler. 

      So, now that you know how a steam radiator works, what does this tell you about problems below?  Let's look at these common issues more carefully.

Which problem do you have?

      But, before we move forward, let's learn how to use your radiator's supply valve.  This is important because most of these issues below and the immediate action you'll most likely need to make in case of an emergency is to cut off the steam to your radiator.  This is done by turning the handle on the supply valve.

How to turn off your steam radiator:

      The supply valve should be located towards the floor close to or right beside the radiator body. It's metal and should have a round handle on top.   It normally looks like this:

steam radiator valve

Keep this valve either all the way closed (clockwise) or all the way on (counterclockwise).

      To turn off the steam to the radiator, turn the handle all the way to the right (clockwise). The radiator should cool down as the steam cools to condensate and air fills up the space inside the radiator. 

      As a warning, remember to keep the supply valve either all the way on (to the left) or all the way off (to the right).  Do not keep the valve turned halfway or somewhere in between.  The supply valve does not regulate the temperature and should only be used to permit or stop the steam from entering the radiator.  

      Read the book by its cover.  If the supply valve is rusted, has a broken handle, or just looks like it has seen better days, look to replace it as soon as possible. 

Problem #1: Too Little or No Heat

      If you're feeling little or no heat, the possible reasons are that the supply valve is closed and / or the air valve is not working properly.  Let's look at these possible issues one at a time:

Reason #1: Closed supply valve

A steam radiator valve - how to diagnose issues for building supers

      The supply valve controls the steam coming into the radiator.  If it's closed, then the steam can't enter your radiator and metal fins will be cold.

      Contrastingly, is the supply valve warm to the touch?  That means the steam has reached the radiator but stopped short at the supply valve.  

     Try turning the knob slightly counter-clockwise to open the valve.  If the supply valve seems to already be open, or doesn't budge at all, then move on to the next step.


      If your supply valve is stuck, you can try to loosen it with hand pressure.  Do not use tools to apply force.  Excess force could break the supply valve and remove the last line of defense against a full blown steam surging into your apartment.  Call in a repair pro or your building super if pressure by hand doesn't work.  As a last resort, replace the supply valve.  

Reason #2: Air valve stuck closed  

air valve for steam radiator_hoffman 40

There are many types of air valves with different functions and for different locations. This one is a "Hoffman 40"

air valve on steam radiator_adjustable type

This air valve is an adjustable type, which means you adjust the size of the steam hole. In short, this valve can be installed on pretty much any radiator along the steam line.

        A failing air valve can prevent the radiator from getting hot.  In order for steam to enter the radiator, the cold air needs to escape from it through a tiny hole in the air valve. If this air valve is clogged or stuck, the cold air will be trapped inside the radiator refusing to let the hot steam enter and do its work. 


      When your radiator body is cool to the touch (or even partly cold) and all else is checked to ensure that there's steam in the pipes, you simply may have to replace your air valve.  

      You can most likely find the correct replacement air valve at the local hardware store.  When you have the right air valve and prepared the work area, you need to shut the supply valve to close the steam to your radiator (But before you do it yourself, read this first!).

Air valve for steam radiator

Problem #2: Hammering, Clanging, Banging or Knocking

      Basically, the occurrences of banging, knocking or other similarly jarring noises happen when the cooler condensate returning to the boiler encounters the hot steam and then a violent expansion and contraction takes place.

      These sounds can emanate from anywhere in the building's heat pipes where the condensate has backed up and its encounter with pressurized steam is unavoidable.

      But, when these sounds seem close by, your own radiator may be the culprit.  Condensate can become trapped at the bottom of your radiator and create a "water dam" that is ripe for an epic showdown with the steam flowing in.

      So, why does this steam condensate pool at the bottom of the radiator and what can you do about it?  

Reason #1: Supply valve turned halfway:

      A common mistake many people make is leaving the supply valve on their radiator partially open or closed on the assumption that the rotating handle can dial the heat up or down incrementally.  The fact is that the supply valve does not control the temperature and, rather, the only two states to set the valve is either fully open or fully closed.  There is no middle ground. 

      When the supply valve is left open in a halfway position, it physically blocks the condensate from flowing out of the radiator while the steam tries to surge in. This violent interaction between the two warring states of H2O takes place and the dread noises are created.


      To solve this problem, first, open your supply valve all the way to let the water drain out.  

      If water remains inside, you'll need to disconnect the radiator body from the pipes and drain the water out.  Water remaining inside the radiator can cause serious problems down the road, so you'll want to address this as soon as possible.  

      As the radiator body is often very heavy and since disconnecting it involves special tools and experience, this should be done by a professional or the Building Super. 

Building super removing steam radiator from supply valve

      If you've found an issue described above, or need any help in doing so, give us a call and we'll be happy to give you a hand. 

Reason #2: Radiator pitch is wrong

      Steam radiators must be pitched slightly towards the supply valve so that the condensate can easily drain out from the radiator (in other words, the air valve side of the radiator must be elevated slightly higher than the other side that is connected to the supply valve).

      If the pitch is not enough to drain the condensate out of the radiator, it will pool at the bottom of the radiator body and block the entry of steam, causing the banging, clanging and other unpleasant noises.

Radiator pitched wrong fixed by Building Super

Sometimes, even the slightest error in pitch can cause problems, such as seen in this photo. I didn't have a bubble level at the time so I used the window sill as my visual marker to indicate how much the pitch was off.


      If you cannot tell by simply looking at it, you can check the pitch by placing a bubble level on top of the radiator. It should be pitched towards the supply valve.  

Using a level to find pitch of radiator done by building super

Checking with a bubble level and ...

Using a level to find pitch of radiator done by building super

... The pitch is good!

       If it isn't, carefully lift the end of the radiator that seats the air valve and try to elevate it by wedging a firm, flat piece of wood beneath the feet just enough to raise it slightly over the other end (with the supply valve).  

Pitching a steam radiator

     There's other ways that a radiator can be pitched the wrong way to cause problems, but this is the most common problem.

     This is a repair that should be performed by someone with experience, like your building super, so read this first. 


      Condensate can be very corrosive to metal and eat away rubber gasket, washer and seal inside the valves. So, if you hear hammering, banging and other loud noises, and find that the pitch of your radiator is off or your supply valve is only partially turned, address this right away. The longer that condensate sits idle inside your radiator, the more damage it can cause to its cast-iron body and valves, leading to unforeseeable water leaks and related expenses.

Problem #3: Hissing, spluttering or other strange noises

      A normal radiator should not emit any noises.  Any hissing, spluttering, spitting, gurgling, whistling or other strange noises should flag that something is wrong and needs to be looked at.

Reason #1: Air Valve stuck open:

      Air valves are meant to release air, but never any steam. Moreover, when air is released through air valve, it should exit quietly. If the air valve releases steam or makes strange noises like excessive hissing or whistling, it should signal that something is wrong with the air valve and that perhaps it is ready for replacement.

      Ignoring these noises can be costly down the road.  

  • Energy (which equals money from someone's wallet) is wasted through the escaping steam
  • Escaping steam eventually reverts to water outside the radiator, leaving destruction on the walls, ceilings and floors around the radiator or even inside the apartment downstairs


      If the air valve is stuck open, you can clean it with vinegar and see if this works to remove any possible blockage.  However, you may want to just replace it, especially since air valves are relatively inexpensive these days and easy to find a local hardware store.

Reason #2:  Air valve wrong size, type, pitch, etc.

      Gurgling or other spitting sounds may indicate that water is getting trapped inside the air valve.  Air valves should not leak or trap any water.  If it does, it may be that the air valve is installed or positioned wrong, or is the wrong type for your radiator.  

Steam air valve diagram

      The air valve should be connected to the radiator by screwing into the radiator body to create a snug, air tight seal.  Condensate may leak when the metal threads inside the radiator body are ruined and not holding tight, or if there's a mismatch with the threads on the air valve, leaving it wiggling loosely.

      Also, you will need to look at the orientation of your air valve. It must be positioned right-side up so that the air hole is pointing straight up, or on some valve types, turned to sit at the highest part of the body.  An air valve shouldn't be leaning over or pointing sideways.

Steam radiator air valve position
Steam radiator air valve- Right and wrong pitch of air valve

       Using the wrong air valve type can lead to similar issues.  

      There's different valves, for instance, with different shapes depending on where or how it screws into on the radiator. 

      There's also different-sized air holes, depending on how far your radiator is from the boiler.  

      So, if you're on the highest floor (furthest from the boiler), the bigger the hole should be.  Conversely, the closer your radiator is to the boiler, such as an apartment on the first floor, the smaller the air hole should be.  The principle behind this setup is that every radiator in the system warms up at the same time and no apartment is overheated before another one starts to warm up.

Problem #4: Water leaking from the radiator

      By far, the most common type of emergency call during the heating season is a water leak from a steam radiator.  The lucky calls are from those who catch the leak quickly from their own radiator.  But, more often are the calls from a distressed neighbor who lives below the leaking radiator and is finding the condensate winding its way - surprise! - down into her apartment. 

      Damages to property and a neighbor's frustration may be reason enough for you to head out looking for possible leaks around your radiator, but the possibility that it can foster mold and mildew inside your apartment or within the cavity of the walls may seal the deal for you to proactively tackle this problem before it becomes progressively worse. 

      Take a look around your radiator.  Are there any traces of water or moisture?  The water may not be visible but if there is a leak, you're bound to see its damaging effects on the surrounding wall or on the floor beneath.  It can look similar to the one in this photo, right at the supply valve shutoff: 

What it looks like when water from steam radiator seeps into wood floor

Water escaping from the supply valve fittings have leaked into the wood flooring, causing warping, deterioration and discoloration - a costly fix if caught too late.

      In this photo below, the source of the leak is apparent - no mystery involved.  Wall damage has appeared where the air valve and its vapor-spewing hole are positioned, a dead giveaway. The damp discoloration at the radiator's foot is also strong indication that the air valve is leaking and should be replaced.    

Radiator caused flooring and wall damage found by building super

      However, it's not always easy to spot where the leak is coming from. That's because the radiator is a piping hot vessel where the two H₂O states of pressurized steam and water co-exist side-by-side, and can escape to the surrounding areas through openings the size of pinholes. 

Steam leaking from radiator

A water leak can be in the form of steam/ vapor releasing from the radiator. YES, this is steam filling up a room! 

Water Leak #1: From the Air Valve 

Coming soon!       

One of the more common causes of water leak is a defective air valve.

Problem #5: Too much heat 

      A radiator pumping out too much heat can be just as unsafe, frustrating and indicative of problems as one that is frigid and seeming not to work. When it comes to overheating, however, only few issues can be fixed from the point of the radiator; most issues are caused by things that are likely beyond your immediate control, such as the boiler control settings or imbalances in the heating system caused by other apartments.

      Even so, the good news is that you still have some options.

Overheating Solution #1: Close the supply valve 

      The supply valve on the radiator controls the entry of steam into the radiator body.  Closing this valve prevents the steam from entering, thereby keeping it from getting hot.  This was covered above here

Overheating Solution #2: Cover the radiator 

      Covering the radiator with an enclosure can help to reduce the heat. Popular options are custom-fitted covers made of wood with perforated metal sheet on its face to allow in some heat, as shown below.

      One urgent reminder: whichever material or style you use for your radiator cover, make sure that it can be removed quickly and its valves can be reached easily in case of an emergency.  Your building super will be thankful if s/he doesn't have to dismantle anything as he rushes to turn off the steam to the radiator. 

Steam radiator covered by custom woodwork

Overheating Solution #3: Paint the radiator

     According to Hunker article "Can You Paint Radiators?"  you can lower the heat output of your radiator by up to 20% by painting them. Silver and bronze metallic paints are best, according to the author.

      Whichever color you decide on, just remember to use high-heat rust preventative paint, such as from the Rust-oleum brand. Lastly, spraying is best method to get paint into the nooks and crannies of the radiator. 

      Oh yes, and do NOT paint the air or supply valves!

Steam radiator in need of serious painting!


Steam radiator that has been spray painted white


Overheating Solution #4: Install a Thermostatic Radiator Valve

      Installing a thermostatic valve can actually help to regulate the heat (in ways that many mistakenly try with the supply valve). 

      Basically, this device consists of two parts: a thermostatic head, which senses the room temperature around it and expands or contracts, and an actuator valve, which closes the flow of air when the temperature reaches a set point.   

      Set the dial on the thermostatic head to your desired temperature, and watch your radiator work like your own personal boiler.

Ways to control steam heat inside a radiator

A thermostatic valve setup (one-pipe steam)

Overheating Solution #5:  Remove the air valve

      Another way to stop the steam from entering your radiator is by removing the air valve permanently, then closing the hole with a metal plug.  Doing this prevents the cooler air from exiting the radiator, thus, creating a barrier for the steam to enter. 

      The plug is threaded so it will screw right into the hole where the air valve once was installed.

Air valve on radiator body

This is not a one-pipe radiator but let's use this photo as an example.

      Remember to turn off the supply valve before attempting this, or during the warmer seasons while the boiler is turned off.

      A warning shared by professionals is not to do this, since doing so creates imbalances in the system.  Ask your building super before you attempt this. 

      Oh, yes, one more thing. It's not in the illustration below, but remember to use teflon tape to create an airtight seal between the plug and the radiator hole.  

      So, we've covered the five most common problems with a steam radiator and the ways to solve them. 

      Discovering them during the winter season and trying to fix them while the heat is on full blast can be aggravating and even dangerous. Is there a way to address to these before the heating season is underway?

      You betcha. 

      The good news is that most of these problems are preventative and can be part of your annual checklist.  if you've read this article, you're already miles ahead in knowing what to look out for.

       To make it easier, I've compiled a checklist below.       

Pre-season Checklist

for your Steam Radiator

  1. Test your supply valve.  Does it turn smoothly in either direction?  Note the condition.  Is it rusty or in good condition? Turn the supply valve all the way off or on. Never in between. 
  2. Visually inspect the air valve:  Is it positioned right-side up?  Are there visible water marks?  If there is evidence of water leaking, replace the air valve.  Remember to use teflon tape, which creates a water-tight seal on the threads. 
  3. Check the pitch: Make sure the radiator is pitched so the condensate is able to flow towards the supply valve.
  4. Check for water damage around the radiatorIf it looks like there's been past damage, check it right away. Don't put it off until the damages get worse, or it even travels to other apartments.  
  5. If your radiator seems like its seen better days, think about giving it a fresh coat of paint with a rust proof high heat paint. 

  • Wow, this is the best round-up of wisdom and tips that I’ve ever seen on the subject (and I spent hours looking for anything some months ago when I had trouble, amazed at how little useful information there was so far). Thanks for creating the go-to page for all this — writing you from the East Village in a 1910-built co-op.

    • Thank you for the compliment! I’m glad my article helped. Good luck in your winter heating adventures in the Lower East Side. Let me know how things turn out!

  • @paul in the other comment…are you my neighbor? Also writing from the East Village – this is an excellent article and I wish I had had this years ago. I live in a prewar apartment that only an engineer could love and the heat has been very tricky. This article would have saved me hours of research and troubleshooting. Great website and great content.

    • East Villagers, you’re not alone! After all that research, I’m sure you could school the engineers. Great work! Thank you for the compliments and good luck heading into winter. Feel free to reach out if you need any help!

  • This was the first article that actually covered all of the issues I’ve come across in the last several years!! All in one place, explained so that I actually understood all of it. Great article!!!!

    • Thank you for awesome words, Tracey! Keep up the diligent researching and learning. You would make any Super feel proud with your persistence. Feel free to reach out if you need any help.

  • What about riser pipes in the bathroom making loud clanging and banging noises what would be causing that ? Before that starts In my apt the heating pipes in the floor above me sound almost like there is a ping pong ball bouncing in them .

    • That “ping pong” sound is the interaction between cool water and hot steam, which can be violent when they collide together because there isn’t a proper path for them to pass each other inside the cast iron pipe (I’m assuming this is a particular type of system – a one-pipe steam system – which is common in NYC).

      Is there an apartment above you? The riser pipe in your bathroom most likely goes up and branches off to feed the radiators in the unit above. Or, the riser can come to an end somewhere up in the floor above. In either scenario, there should be an air valve at the end of that pipe that should be checked for normal operation. And it sounds like somewhere the water is getting logged / stuck / pooled. The super should check to make sure the radiator and the pipes are pitched properly to allow the water to drain out easily and completely.

  • So glad to have found this site! Super helpful!

    I have the same issue as @Mary. And the riser pipes leave chips and dust of what I think is the pipe itself…that is, the paint on the pipe is silver and dust around it is a rusty brown color so I’m guessing it’s the pipe…in any case, it’s annoying and am constantly cleaning the area around it.
    I live in Brooklyn in an early 1900s building.

    • Hi Melissa, I agree that the flakes may be indications of corrosion on the pipe. And the flaking chips may be due to a couple different issues. I’ll try to explain the main reasons here.

      A riser pipe is like a “highway” for steam to shoot up the building floors. This highway travels up through openings in the ceiling and the floor between the floors, openings that are often sealed with plaster. As the building shifts slightly over time (this is normal), the plaster around the riser can break and exposes a gap. It can also disturb the paint on the riser.

      These gaps can then serve as the perfect pathway for water to travel down if the bathroom above you springs a leak or spills water. Also, at the top of the riser may be an air valve sticking out from it. If this air valve springs a leak, or if there’s a leak from the bathroom above, the water will most likely slide down the riser through the opening and wet the riser along the way. Rust happens when the paint has chipped away to expose the metal pipe and there’s a combination of moisture and oxygen on the metal for a prolonged period of time.

      But, as the water travels, it will also wet plaster and wood objects, like wood joists. When it does, water may carry the colors of these objects, such as brown color from rotted wood; and then it will dry and flake off or leave brown streaks on the riser pipe.

      So, the rusty brown debris that you find may be rust or it could be something less insidious. Still, I would check to see if there is an active leak upstairs that is causing this. If everything has been resolved, ask your building super to scrape the plaster around the riser pipe and reseal any openings. Finally, if there is rust on the pipe and it is not badly rusted, the super should scrape the rust off and apply the right paint and primer (high heat) to seal the metal.

      I hope this helps, let me know if you have more questions on this!

  • Hi , I have a radiator that is very slow to warm. the pipe and valve get hot soon after the heat is turned on, but the actual radiator takes forever to warm up. Only the top also. the bottom doesnt get warm. Is it possible the bottom has debris in it preventing steam from entering? There are puffs of air coming out of the vent on the other side (ive removed and hole is breathing). My next move is to remove radiator and try to flush it out? Do you have any info on this situation? any recommendations? is this slow heating normal? Its encouraging that the service line and valve get super hot, that means the steam is delivering, it just seems to be the radiator not taking the steam. Thanks.

    • Hi Jeff, you’re on point that the issue appears to be local to the radiator itself. Piping, supply valve and the top of your radiator becoming hot is a good sign that your boiler is working and everything is more or else normal… that is, until it reaches your radiator.

      From what you are describing, it does sound like something is blocking the steam from filling up the radiator, maybe water condensate, debris or air.

      Water gets trapped when the radiator isn’t pitched properly. You could check to see if it is pitched properly with a simple visual check (with a level, if you have one). Are there any abnormal noises like banging or knocking?

      Draw a mark on the radiator with a pencil where the temperature changes from hot to cold. This mark may be where the steam can’t get through. Tap a thick metal stick lightly on body above and below the mark and see if it sounds denser below the mark. If so, it could be water or debris. If it sounds hollow all the way down, it may indicate that air blocks the steam inside the radiator. This works on some but not on all radiators.

      Changing the air valve is an inexpensive way to see if blocked air is the cause of this. Replace this with one that has a larger vent hole than the one you have. If you can email me a photo of your air valve at info@sparksuper.com, I can help you find the right fit air valve (remember to turn OFF your supply valve and let the radiator cool a bit before removing your air valve!).

      Lastly, make sure the supply valve is fully open. Defective supply valves can get stuck wholly or partially. A supply valve where the temperature changes drastically, from hot to cool, from one side and the other while the dial is fully open indicates a blockage problem.

      Feel free to email me if you have any questions.

  • Thank you for such an informative article. Own a 1884 brownstone in nyc and always always have heating problems
    Watching steam and water come out of the steam valve and started searching the web
    Big Thanks

  • Regarding the proper sizing of vent holes based upon lower vs upper floor location, this article contains one error common to all internet articles I have seen. I lived in a 4-story steam-heated apartment building in which the first floor tenants constantly complained of inadequate heat each winter, whereas those of us on the upper floors cooked to the point of turning off most of our radiators and cracking open windows. The frustrated landlord struggled but never could solve the problem, but it was simple, the lower floor vents were adjusted to the smallest vent holes, whereas the upper floors had the largest.
    For the past 30 years I have lived in my 1935, steam heated home. I found the vents set to the same backwards sequence. I immediately reset them, replacing some (be sure to buy those that are adjustable). The result is the system pumps out heat in the worst arctic blasts and does it evenly. The principle is simple: when the furnace kicks in the steam races to the highest point in the building, where the small vent holes create back pressure, which forces steam down to the next level, and so on down to the lowest floors, where the wide-open vents welcome any steam they can get.

    • Thanks for sharing your experience and for pointing out an interesting issue, Joseph. I think we are both on the same page in the idea that an important function of an air valve is to ensure an even distribution of heat from the radiators in the building within a given time, no matter where the radiator is located. The goal is to heat every apartments at the same time and with the same intensity.

      On this principle, to have air valves with the smallest hole on the upper floors and valves with the widest holes on the lower floors runs contrary to my experience since the lower floor radiators are apt to get hit with pressurized steam first, causing these apartments to cook before the upper floors got warm.

      Would it be possible to let me know the layout of this building or house? Is this building much longer or wider than it is high? In such a case, I can see how a radiator in the lower floor that is located farther in distance from the boiler (source of the steam) than radiators in the upper apartments can have such a problem. Let’s say, a building with two or three floors but run the length of a city block.

      In that case, an apartment on the lower floor may actually be much further from the boiler than one located on the top floor. Thus, these lower apartments would need air valves with larger holes to help compensate for the longer horizontal distance and allow the steam to push the air out of the system faster. A small hole would slow down the steam from reaching its radiators, creating the cold conditions you’ve described above.

      By the same token, the upper floor of this short and wide / long building would receive a faster blast of steam than a radiator on the far end of the building. A larger hole of the air valve, in this case, would overheat the upper apartments since they are closer to the boiler than the lower apartments. To solve this, the air valve would need to be switched to one with a smaller hole to help keep the steam at bay. These measures would help balance the heat distribution in the building.

      Would this describe what is happening in your building / home?

      • The apartment building is a 4-story with (8) 2-bedroom units, in Cincinnati, built 1905, so with high ceilings it is not much longer than it is tall and wide. The home is a 3-story (technically 2-1/2) “salt box”, so again, closely proportioned.

  • I have changed air valve but still releases steam from air valve ( Home Depot ). I donnt believe had a name but non adjustable. I’m just intrigued as if the 2 new valve are defects that won’t hold steam. I get constant noise and steam real ease from hole

    • Like you, I also doubt that you’ve purchased two lemons. Are you certain that the other requirements are met, such as the radiator being pitched properly towards the supply valve? Or, maybe your radiator cast iron body has water trapped inside it? Also, did you purchase one with the correctly-sized hole? If you’d like, send me some photos at info@sparksuper.com and I’ll see if I can spot anything in terms of visual clues to your issues.

  • This article should be a MUST read for anyone who is using steam heat!! I have read countless articles on the subject of Steam Heat and none can match the level of detail and your eloquence of simple explanations.
    Us fellow steam heaters are very appreciative of your efforts in writing this article and responding to our many questions.
    I was told at an early age that you need to periodically open the boiler drain valve until the rusty water runs clear. I suspect this is to remove sediments from the boiler. At the end of the season my bucket has about 1/8 – 1/4 inch of rust sediment. Should I be worried?

    • Thank you so much for the compliment, Mitchell!

      Happy to say that your mentor imparted sound advice to you when you were young. Generally, flushing the boiler is a critical maintenance task to prolonging the life of your boiler and for keeping it going without the common failures. The sediments that enter your boiler system can cause many frustrating issues, such as clogging / jamming / disabling the low water cut off.

      When flushing the boiler, the water will carry brownish color and sometimes even be viscous, like chocolate milk. This water should run clear when flushed provided this task is performed on a regular basis and the boiler is maintained by a professional on a yearly basis.

      So, you may be asking whether the sediment at the bottom of the bucket is rust that is indicative of some sort of deterioration of the surface inside your boiler or from its parts. And if so, whether 1/8 or 1/4 inch is an alarming presence.

      My thoughts? Not necessarily. Cold water from the street can carry sediment into your boiler, which can circulate and settle inside your boiler. When the boiler is flushed, this stirred-up steaming water carries some of it, which ends up inside your bucket. If 1/8 inch to a 1/4 inch is what is remaining after an entire heating season of flushing (at least 32 flushes or more), it’s not too bad.

      I think a better indication would be the length of time that the water must run before turning clear when you flush it. Also, whether your sight glass (which indicates the water level inside the boiler) is clear or not. If the sight glass is clear, as well as the water inside it, and the glass is not caked with rust-like particles, or if your water runs clear within a few seconds, then I would not be worried.

      A final way you may want to check (but you should have a professional with you) is to let the water out from a drain at the bottom of the boiler and see if this water runs clear or not, as sediment turns to sludge at the bottom of the boiler and this can tell a lot. Of course, without fully opening up the boiler to really examine the innards, these measures are only guesstimates.

  • Great info thanks…..however my problem is….I have a 1924 old home with a 2 pipe steam/condensate return system. Radiators at end of the line get little or no heat. These radiators have no air vent valves and I see no plug on the body of the radiator to put one.

    • Hi Tom, thanks for your inquiry. In a 2-pipe system, there should be a device commonly called the “trap,” versus an air valve, that removes the air and water from the heating system. This looks different from an air valve discussed here and cannot be plugged like a one-pipe radiator. The trap allows the steam to circulate properly and heat the radiators on its line (such as those located further away at the end of the line). If the radiator is not heating, it seems that you may have a problem with the trap. This article discusses a one-pipe system, so feel free to contact me at info@sparksuper.com. I can help provide you with some basic one-on-one troubleshooting tips on a two-pipe system to point you in the right direction.

  • I just got a new unpainted radiator in my apartment. Yesterday was first time the building turned the heat on this season but i noticed steam coming out of it but not from the valve. Is that supposed to happen? And there is a bad metal like smell.

  • Such a helpful article, I have referred to it many times while attending to my steam heat system. In such a hard industry to get non-expensive advice in- I truly am so grateful for this resource!

    • Hi Gretchen, Thanks so much for reading and for the awesome compliment. Glad you’ve been helped. Reach out to us to let us know it turned out.. Happy heating season!

  • Would love to see Water Leak #2: leaking from connection of radiator to valve. I took it off, inspected the surfaces, which seem to be smooth on both sides. I read somewhere it’s OK to use pipe dope or automotive-type RTV silicone sealer, if just re-mating them doesn’t work. Any suggestions for how to ensure alignment, how tight to torque the ring, and whether to use any sealant compound?

  • This is a fabulous summary of many years of experience and wisdom about steam radiators. I have lived in homes with one-pipe steam radiators or two-pipe water radiators for more than 60 years. I have seen every problem described here. I am going to print out this article and save it as a good checklist for the next generation.

    • Rich, thank you for your kind words of encouragement and for passing it forward. Two-pipe systems – this itself is a great topic with its own set of complications, as you’ve likely experienced. You’ve inspired me to cover it in the next article 🙂

  • This is officially my boiler Bible! Thank you so much for such a well-written, informative, and instructional article. This is everything I always wanted to know about radiators.