Radiator valve with air bleeder (C) Daniel FriedmanRadiator Valve & Vent Control FAQs
Questions & Answers on Hot Water & Steam Heat Radiators & Controls

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Radiator valve inspection & troubleshooting FAQs:

Frequently-asked questions and answers about the use, adjustment, diagnosis & repair of hot water or steam heating radiator valves & steam vents to control heat output from individual radiators.

What to do about hot water or steam radiator valves or vents that are stuck open or closed.

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Radiator Valve Questions & Answers

Thermostatically controlled hot water radiator valve (C) Daniel FriedmanThese questions & answers about radiator control valves were posted originally at RADIATOR VALVES & HEAT CONTROLS - topic home. Be sure to check that article if you have not already seen it.

On 2017-12-13 by (mod) - get better radiator flow-through with ball valve + Danfoss thermostatic radiator valve.


I may not understand the situation correctly, but I agree that when there is a thermostatic radiator valve installed one would leave the main valve fully open.

Both ball valves and gate valves are designed to be used in the fully-open or fully-shut position.

If your radiator has a globe valve you'll improve its flow by replacing that with one of the other two designs.

Other readers: Definition of Kv - The Kv-factor is a calculated parameter that gives the capacity of a valve expresed as its water flow through the valve in m3 (or 1000 lites) per hour at a pressure drop across the valve of 1 Bar. Kv is useful when calculating relative pressure drops among different valves used in piping systems.

At PLUMBING CONTROLS & VALVES we explain the differences in operation and flow properties among the three basic plumbing valve designs: globe valves, gate valves, and ball valves. Because spherical ball valves fully open the water passage when the valve is open these valves do not produce a significant pressure or flow-rate drop across the valve.


Boysen, Herman, Kv: What, WHy, How, Whence?, [PDF] Danfoss, (2011) retrieved 2017/12/12 original source:

On 2017-12-13 by Chris (

My radiators are equipped with Danfoss thermostatic valves. Since those valves are sort of globe type valves and I set them always fully open, I wonder whether using simple ball valves instead, will be more effective in terms of better heating the radiators because they do not disturb the water flow as the globe valves do.

From other side, Danfoss valves have a Kv nozzle that might improve the way the water entering the radiators. Please advise. Thanks in advance.

On 2017-11-26 by (mod) - what do the numbers mean on my thermostatic radiator valve


I'm not sure what number is here asking about but I'm guessing they are index numbers on the control valve of a thermostaticly operated radiator valve.

If those numbers correspond to specific temperatures, which I doubt, that would be documented in the installation guide for the valve. If you can see a brand name and model name on the valve I can look up that information for you.

Most likely however the numbers are simply relative with 8 being highest and 1 being lowest setting for temperature.

If your radiator is cold, most likely the problem is not the adjustment position of the valve but rather that the heating system or its pipes are radiators are Airbound and need to have the air bled out of the system.

You can use the on-Page search box to find out article series on

AIR BOUND HEATING SYSTEM (Also found in INDEX to RELATED ARTICLES at our Continue Reading suggestions at the end of this article)

To see how to diagnose and repair that condition

On 2017-11-16 by sabrina

what do the numbers mean? mine goes from 0-8 1/2 my apt is cold how do i get all the rooms on the same temp? or how do i make more rooms warm and my room less warm?? HELP ME MY KIDS ARE FREEZING AND I AM DYING IN THIS HEAT

On 2017-11-26 by (mod) -

No, look for a leak at a drain opening on the side of your control valve.

On 2017-11-23 by Tracy

Should water cme out if control valve if turned fully open

On 2017-11-10 by Leona

I have a hot water system, but one radiator is not working. There are two pipes coming from the floor...the one on the right is warm, and the one on the left is cold (as is the entire rad). I tried bleeding it, and only cold water came out (no hissing or air).

Upon looking at the other rads in the house, they all seem to have a valve on the left pipe, but for some strange reason this particular rad has no such valve anywhere. All the other rads in the house are working perfectly, so I'm perplexed why this rad has no valve, and if there is one, where could it be, or could it be coupled with another rad somewhere, like perhaps one that's in then garage. Will gladly supply pictures if it will help. Thank you. Leona

On 2017-06-04 16:00:47.479690 by (mod) - replacing a full size radiator in a steam system with cast iron base.


What we need to figure out is the btu output of the existing radiator that you have. That's generally done by looking at the radiator size, number of sections, or radiating area. Armed with that information we can look at the btu output per linear foot of the baseboard that you want to install.

You then have the option of installing enough feet of baseboard to match the original BTU output of your radiator. There are of course other options such as simultaneously reducing air leaks and improving insulation in the space being heater. I've done that when I could not get enough linear feet of baseboard. It works very well.

I wanted to add that changing from radiator to baseboard would not be a legitimate cause of banging pipes

On 2017-06-03 by Ron H

Can anyone advise on replacing a full size radiator in a steam system with cast iron base. I need to go to base as additional room is needed and the existing radiator won't fit. I think that this might cause knocking but I am not sure. Do I need to run a return pipe down to the basement. Is there a feasible way to make this work? thanks.

On 2017-03-10 03:26:49.170553 by (mod) -

It needs to slope to the drain valve or it may become condensate blocked

On 2017-03-09 19:46:50.889076 by Mike

who can tell me the proper installation recommendation of a typical residential one-pipe steam radiator, i.e. is the rad "required" to be slightly pitched back toward the valve OR will it function normally if level? Thanks, Mike

On 2017-01-15 15:20:36.322719 by (mod) -

It sounds as if the valve is broken internally. That is, if you can turn the radiator control valve handle but it doesn't let heat into the radiator, then most-likely the valve stem has broken off from the valve gate.

When you turn a radiator valve handle the handle turns a valve stem = a rod. The rotating rod has, inside the valve, a coarse screw thread that causes an internal gate to move up or down to open or close the valve opening that in turn lets hot water or steam through the valve.

In some valves the stem can break loose from the gate, so the stem turns but inside the valve nothing happens.

Other snafus include debris clogging inside a valve but on radiators I think that's less likely.

On 2017-01-15 13:32:03.476850 by Jenny

I have a cast iron baseboard in my kitchen and bedroom, sumilar to the one Margaret posted, and two regular cast iron ones in my living/dining room. I realized the other say that the one in my kitchen was ice cold when the heat came up yet all the other ones were hot. I removed the valve on the kitchen one(which is a basic, small, open and close valve) and within minutes the heat started flowing through again.
Is my valve broken or is it just stuck?

On 2016-10-28 02:41:51.500102 by (mod) -


If the new valve is the wrong model or was improperly installed or is damaged or defective it cannot vent air out of the radiator and the rad won't get hot. But before calling the repair person back to the job, check that the control valve for the radiator is indeed turned on: opened fully counter-clockwise.

On 2016-10-27 23:33:18.111075 by (mod) -


We repeat your question and give a detailed step by step reply near the bottom of our article on radiator air bleeder valves:

On 2016-10-27 16:12:55.038925 by Nicci

Hi, my son has a convector radiator in his bedroom which desperately needs bleeding, however the inner part where you enter the key has broken off so i'm unable to turn to let out air. Can anyone please advise whether it's still possible or whether the radiator would need new part?

On 2016-10-27 00:23:33.850274 by Jill

I just replaced my old Steam Air Vent valve because it was spitting with a new one as suggested by my plumber. Now the heater no longer gets hot. All other heaters are working. Why would a newly installed valve not work???could I have screwed to tight? I also put recommended tape on the stew part threads???

On 2016-10-25 22:14:00.810130 by (mod) -

At the cost of having no heat you can turn off the valve - as a temporary fix, while you wait for the plumber to repair or replace the valve. I'm assuming that's the location of the leak.

On 2016-10-25 17:32:07.609209 by Alfredo

My steam radiator bleeding air with bubble what can I do

On 2016-10-23 23:51:30.982296 by (mod) -


For help with using steam vents, please click on the live link GUIDE TO CHOOSING & INSTALLING STEAM VENTS. found at the bottom of the article just above. Let me know if then questions remain.

On 2016-10-23 18:32:30.434615 by Eddie

With a one pipe convector steam system, and two floors,with six wall units on the first and second floor, using vent-rite air valves,what air pressure valve should be used on the first floor, 3 psi or 6 psi?

Two Pipe steam radiator (C) Daniel Friedman

Reader comments:

(Nov 7, 2012) Anonymous said:

Great articles here. Very informative.

(Jan 11, 2016) sharon said:
thank you for very clear,detailed information.

Question: steam vent won't close

(Oct 24, 2011) Lisa said:

Trying to figure out vent problem without calling plumber before heating season. Last season one room was totally ruined by steam and dining room seemed to have too much steam. New vents installed on radiators when new gas steam unit installed 6 years ago. Vents have #s on them. Should I put it on lower #?


Lisa i would need to see a photo of your steam vent or know the brand and model number to be specific. But if you have steam vents that never shut off when the radiator is hot, and if adjusting the vent doesn't solve the problem it sounds as if the vent needs to be replaced. . A properly operating steam vent will stop venting air (and a little steam) when it gets hot.

See STEAM VENTS - home

Question: can't get air vent valve out of the old radiator

(Sept 20, 2012) donna said:

We just bought an old home and the one rooms radiator air value must be broken so I can't put another in how
do I get the broken piece out



The options are to try a bolt extractor to remove the broken part or to drill out the broken part and tap new threads in the drilled hole. Then to reduce the enlarged threaded opening to a standard air bleed valve NPT size you may find a helix insert at an auto or plumbing supplier.


Question: removed two pipe steam radiators - want to turn on heat

(Oct 10, 2012) Mike said:

I am currently renovating a room in my house and I removed two two-pipe system radiators. I am not ready to re-install them yet but I would like to turn the heat on. Will shutting off the valves be enough or will I need to cap off the traps as well?


Heat will work in the other radiators provided they are not fed by the pipes you close off and that their return condensate lines are similarly not interrupted. You'll need to follow the steam piping to make a sketch for yourself to see that this is the case.

Question: wants to buy adjustable thermostatically operated steam vents

(Oct 11, 2012) Anonymous said:

Can you please tell me where I can buy the Adjustable Thermostatically-operated steam vents?


Sure. Several companies provide thermostatically-controlled radiator valves including Armstrong, Danfoss, Hoffman Specialty, Jacobus (Maid'O'Mist) and others. The automatic radiator valve shown at left was observed on a typical modern European installation in Molde, Norway.


Question: convector radiator valve leaks at screwdriver adjustment point

(Nov 20, 2012) Brent Hoffman said:

On my hidden manual convector control valve, how or can i clean and repair it so i can adjust flow with out it leaking at the screwdriver adjustment point. The last time I tried to increase the flow by turning the adjustment screw, I almost didn't get it to stop leaking. Is it like a faucet that I can open and get replacement parts to repair and rebuild?

If so, if I lower the expansion tank pressure noting the current pressure first, will that allow me to repair the valve with out loosing water? If i loose water in my convector boiler system, how do I refill and know when it is full. Each one of my convectors feed from a 1/2 service line with a 3/8 feed line to the convector and return through a 3/8 to a 1/2 return line, i do not have a series system loop.


Brent, it is sometimes possible to disassemble and clean up the small screwdriver-operated valve you describe but I've not had much luck with that approach. With heat off and pressure off of your system, remove the old valve, take it to your heating supplier and buy a replacement - they're not expensive and you'll actually save time and trouble as well as money.

Question: heat won't turn off

(Nov 28, 2012) Aimee said:

Hi there, i really need some help . My radiator is really hot even though i already turn off the switch. Are there anything wrong ? If some thing wrong , please let me know ? thank you so much .


Aimee a hot water or steam radiator will continue to radiate heat for a time even after the thermostat stops calling for heat. That's normal. If the radiator never turns off then the call for heat is not turning off. In that case

Question: strange boiler noise and no heat

(Nov 29, 2012) Sof said:

Hi,I had some painters over to decorate and they turned off the radiators so the wallpaper wouldn't shrink whilst drying. Normally, to turn the heating on I just push the 'On' switch on my boiler.

Now though, by doing so the boiler makes a bit of a strange noise. The water stays freezing cold and the radiators wont heat up even though I've pushed the 'On' button. This means that the builders turned the heating OFF elsewhere to ensure I don't turn it on. Now my house is freezing and the water's too cold to was up or have a shower. What could I do?


Sof there is a more basic problem than at the radiators - see NO HEAT - BOILER for a sequence of things to check.

Question: steam enters at top of some steam radiators

(Jan 5, 2013) Caroline said:

Hello, I just wanted to inform you that you need to correct the information on your site. This section: Types of Radiator Valves: Hot Water vs Steam and the the statement "because first, the valve is mounted at the top of the radiator (water, not steam - steam enters at a radiator bottom but sometimes so does not water; the reverse is never true" is not correct. We have a two pipe steam radiator system and the valve is mounted just as shown in this picture - so our steam does enter from the top of the radiator.


Thank you Caroline, we've reviewed and clarified the text on this point.

Question: radiators don't get hot unless I remove the steam vent

(Jan 7, 2013) Cesar said:

We have two radiators that don't heat up unless I remove the steam valve. When I unscrew it a blast of air comes out and it starts to heat up. We figured the valves were clogged but they're not because when we screw them back on we can hear steam hissing out. My question is this: why doesn't it release the steam all on its own? why do I have to remove the steam release valve in order to get it going?



The steam vents on those two cold radiators are not working as they should. Take them to your heating supplier and buy new equivalent replacement units and your radiators should work perfectly again.


Question: different steam vent locations on one pipe versus two pipe steam systems

(July 12, 2014) Jerry said:

I have a few questions on one and two pipe steam systems. On one pipe systems, why is the steam vent located down low on the radiator and not high up like on hot water radiator systems. What would happen if it was located high. My question on two pipe steam systems is why no vent is needed on radiator? What would be the result if one was installed?


Interesting questions

In a hot water radiator the air will be just at the top of the radiator so we put the air bleeder there.

In a steam system the whole radiator is filled with air when cool and is vented automatically by a steam vent placed to vent rapidly and to close at an appropriate time as steam enters and the radiator becomes hot.

Placing the steam vent at rad top may lead to overheating. That may explain why usually on steam radiators the vent is on the radiator side.

If you see a working 2 pipe steam system without a steam vent the air along with condensate must be vented via the return line. I do not agree that vents are unnecessary on either system type. If there were no way to push air out of a cold steam radiator then the steam won't enter it and the radiator won't get hot - you'll have cold steam radiators and shivering pets.

Question: one of my radiators won't get hot, what should I do?

(Dec 6, 2014) chris said:
I have four hot water radiators and one is not getting hot, even at the inlet pipe. what to do?



If your radiators are hot water (hydronic) and not steam, then try bleeding air out of the radiator.


Readers with steam radiators that won't heat up should see COLD STEAM HEAT RADIATORS

Question: what to do about an air valve leak and occasional water droplets at a steam radiator

(Jan 1, 2015) Anthony said:
I discovered a leak from my bathroom steam radiator. It involved a leak from the air valve in occasional drops. Now this radiator had a cover so it was not known for quite awhile, long enough to show my ceiling below wall paper separating the seams. This radiator also had wooden stops under that valve end to slant it towards the on/off valve. The wood was saturated from the slow drops. I replaced it with new similar vent valve and of course the radiator got warm, but i hear no hissing. As for a new valve shouldn't one hear loud enough air coming out of the vent? If not, is there any concern?


Not all steam vents are equally noisy, but when heating up from a cold condition I would expect some air discharge from the vent.

If there is no air venting at all from a steam radiator vent then the vent may not be properly set or it may be the wrong model.

Question: tepid radiators on third floor

(Jan 4, 2015) Anonymous said:
On the third floor of my house, the radiators (hot water) are hot in one bedroom but only slightly warm in the bathroom and other bedroom. I bled them and there was no air coming out only tepid water. I was wondering if draining this cooler water out of the radiator would help.



I am doubtful that draining further water at the cool radiators will help because I suspect that there is an air blockage in the piping between the hot radiators and the cool ones. Rather, if there are not other air bleeders in locations that release that trapped air you may need to use one of the more aggressive measures:

See AIR-BOUND HEATING SYSTEMS for steps in diagnosing and repairing this problem

Also for tall buildings, consider that the boiler pressure could be slightly too low


Question: steam radiator doesn't get hot

(Jan 10, 2015) Anonymous said:

I have a 75 year old steam system and one radiator doesn't get hot. It gets warm only at the end of a heating cycle. I put a new release valve on it. No help. I can easily turn the radiator control valve open and closed and I see the stem below the knob rising and falling as I do that. Despite this appearance, can the valve inside be stuck in a partially open position?



If the new steam vent didn't fix the cold radiator,

1 the radiator valve could be broken internally so that even if the stem rises the gate does not open properly - this is particularly true with gate valves

Valve types are illustrated at PLUMBING CONTROLS & VALVES

2. the radiator condensate return could be rust clogged or otherwise blocked (condensate is not draining out of the radiator)

See COLD STEAM HEAT RADIATORS for detailed cold steam radiator diagnosis and repair help.

(Jan 14, 2015) Anonymous said:

Thanks for the reply DanJoe. When I changed the vent (I put a 6) I noticed the radiator was slightly tilted the wrong way. I adjusted it to tilt a little towards the valve. I have other radiators in the house that have always been tilted wrong yet they heat up fine and I leave well enough alone on those.

After two days the problem radiator seems to be getting a little warmer at the end of each cycle. I'm going to wait a couple more days and see. I guess it could be clogged like you said with rust and the steam may hopefully clear it out. I really hope that's the case because I don't want to remove this radiator. It's pretty heavy and wedged in and I think it'll be a pain to do.


If steam is entering the radiator you'll usually know it by hearing the steam vent operate.

Question: how to (ball-park) select air-vents on a multi-story 1 pipe steam system

(Jan 15, 2015) Larry said:
(like the site) looking for some information on how to (ball-park) select air-vents on a multi-story 1 pipe steam system (max psig < 5 ). i notice that on the 1st floor there is a no.6 vents and on the 3rd floor no 40 vents.. are these vents right? how do i make sense of these thing? thanks.

Sorry not sure if psi (absolute) or psi (gauge), but since steam can exit the system I assume it is called psig.



I can't reliably design for your steam system by e-texting.

I'd simply give a local supplier (who sells steam vents) a call to ask for their technical expert - describe your building, steam system., heights, operating pressures, volumes, and she or he can recommend vent models for you . If you can't find a local expert call one of the vent companies we list directly. They know their products in exquisite detail.

(Jan 15, 2015) Larry said:
Thanks for getting back to me, right after sending the question I kind of realized was a bit much for a Q&A forum. I'll ask my fuel oil supplier for a local recommendation. Again, thank you for getting back to me.

Larry we do appreciate questions - they help us know where to research and provide more information. But sometimes a thoughtfully-succinct question leaves me worried that we know so little that we might give dangerous advice.

I should have pointed you to our summary of steam vent sizes, choices, selection guidelines in the

Steam vent capacity and features are summarized in tables we give at STEAM VENT TYPES, SELECTION

but frankly it was late at night when I replied before and I just forgot.

Question: what are the numbers on the radiator valve on my steam heat radiator? How does this valve work to control heat output?

Armstrong thermostatically operated steam vent (C) Armstrong International(Jan 14, 2016) Anonymous said:
I have a one pipe steam heating system with a control opposite end of the intake pipe. It has numbers. How does it work? Can I control the heat output with it. The system is vewy old.


I think you are describing a thermostatically controlled radiator valve. If that is the case turning the valve to a higher number will generate more heat. The valve contains a heat-sensitive control that opens or closes valve based on the number setting on the valve and room temperature.

Question: how do I use individual radiator valves to control heat?

(Feb 13, 2016) Debbie said:
One thermostat downstairs in living room radiators in all rooms how do I use valves on each radiator to adjust to a proper heat



Closing an individual radiator valve will reduce its heat output or if the valve is fully closed, no heat should emerge. Turn clockwise to close a valve.

Watch out: if a valve is stuck don't force it as you may break it.

Question: century-old radiators, valves do not turn even one full rotation

re posting

AUTHOR:Mark (no email)
COMMENT:I have old (century home) radiators, the valves only turn approximately 300 degrees from 'fully open' to 'fully closed' does this sound right? Is it actually reaching the fully closed position?


If turning the valve is not making a change in how the radiator performs I suspect the valve stem has broken away from the valve gate internally.

Question: radiator valve leaking at valve stem, now I can't turn it

(Feb 17, 2016) Noel said:

So I made a big mistake. I had a radiator that was leaking air from the valve stem. So hissing from the vent and then after it reached full steam, slight leaking and more hissing from the valve. I watched a youtube video showing that using graphite packing on the valve stem would fix the leak.

Well I overtightened, overpacked, and now the valve is unturnable, even with the packing nut completely off. I took a dental pick scraped out as much packing as possible from the root of the stem but the space is too small even for a dental pick. Is there anything I can do to fix the valve? I've read nothing dissolves graphite. I believe it's stuck in a partially open position. Radiator does heat up. Is my only option at this point to replace the valve?

I should add that this is a one pipe steam heat system, so it should only be fully open or closed. Though I have not yet noticed any ill effects of being partially opened.


HI Noel. Yeah things often go bad.

After removing the valve handle and then removing the valve packing nut from the stem, you should be able to unscrew the valve using a Vise Grip tool. In the worst case, if the stem snaps, the whole valve will have to be replaced, but, then, that's where you are before trying the Vise Grip approach. Possibly dripping a little WD40 or Liquid Wrench around the stem and letting it soak in will soften the graphite-impregnated string and make removal easier. So try that and let things soak for 20 minutes before trying the Vise Grip approach.

BE SURE that heat has been turned off and the system is cold. Otherwise you could get a steam burn.

Question: how to turn off the heat at a radiator

(Apr 23, 2016) Doctor said:
Which setting should it be put on now? To avoid the heat staying on during this season...
flag like


If you live in the northern hemisphere, in which case spring and summer are approaching, you would simply expect that the ambient temperatures will be above your thermostat setting and no heat will be called for by the thermostat.

If you simply close the radiator valve, which would mean turning it clockwise, that of course would prevent heat from entering the radiator. But it will not prevent your heating boiler from running.

You can of course lower the thermostat setting to a very low number say 50, and that also will help ensure that he never runs during the summer.

Or you could turn off the electric power to your heating furnace or boiler, just don't forget to turn it on in the fall.

By the way during the time that you were out of the heating season is a great guy to have your heating system cleaned and inspected.

Question: steam vents set to 3 psi or 6 psi?

2016/10/23 Eddie said:

With a one pipe convector steam system, and two floors,with six wall units on the first and second floor, using vent-rite air valves,what air pressure valve should be used on the first floor, 3 psi or 6 psi?



For help with using steam vents, please click on the live link GUIDE TO CHOOSING & INSTALLING STEAM VENTS found at the bottom of the article RADIATOR VALVES & HEAT CONTROLS where you posted this question. Let me know if then questions remain.

Question: bubbly water coming out of steam radiator - what do I do?

2016/10/25 Alfredo said:
My steam radiator bleeding air with bubble what can I do


At the cost of having no heat you can turn off the valve - as a temporary fix, while you wait for the plumber to repair or replace the valve. I'm assuming that's the location of the leak.

Question: no heat after replacing steam vent

2016/10/26 Jill said:

I just replaced my old Steam Air Vent valve because it was spitting with a new one as suggested by my plumber. Now the heater no longer gets hot. All other heaters are working. Why would a newly installed valve not work? could I have screwed to tight? I also put recommended tape on the stew part threads?


Jill, I suspect the steam vent is the wrong type or is damaged if it's not allowing air to push out of the radiator. Or perhaps your teflon tape covered the air inlet into the steam vent.


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