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.

Radiator Valve Questions & Answers

These 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 2019-10-26 by (mod) -

Thanks for the follow up. Certainly shouldn't feel silly. The only thing silly about us is in chicken to ask a question. And nobody knows it all.

See details of air bleeder valves on heater convectors like yours (below) found at

AIR ELIMINATOR / FLOAT VENT REPLACEMENT

On 2019-10-25 by Greg

Nevermind, I figured it out (and feel more than a bit silly). There's a large flap on the inside, and the knob in the middle turns a screw that moves it to let more or less air through. Awesome, thanks. Any idea what the knob in the middle is for?

It seems to spin freely for a long time before stopping.

On 2019-10-23 by (mod) -

Greg,

That is an air bleeder valve used to remove air from the hydronic or hot water heating line at the high or Final End of the heating convector unit.

There is a variety of exact design for those bleeder valves but typically a center screw or not his loosened to permit are to vent through a small opening in the device.

You loosen the screw.

If are hisses out you leave the vent open for a few seconds until the air stops at Water begins to appear. At that point you vent to the air at that location and you can tighten the screw.

If only water begins to come out at that vent when you loosen it then there is no air at that location and you simply close it again

On 2019-10-23 by Greg - externally-accessible air bleeder valve on a heating convector unit

Sorry for the late reply: This is an image of one them [shown above]. The other side is smooth (nothing on or in it).

On 2019-10-13 by (mod) -

Greg

Please add an image or two (one per comment) so that we can see what we're looking-at

and then I can comment further

On 2019-10-13 by Greg

I'm staring at a radiator with an odd valve placement: One knob in the front close to the top (that seems to freespin; a thing in the side that looks like a set screw with a nut around it.

How does this style operate?

On 2018-12-10 by (mod) -

Excellent, Adam, thank you for the follow-up, as that will help other readers whose radiators are working but just not hot enough and where a Dunkirk boiler is installed that uses the company's Economy Feature on the controller. For other readers, here is what the Dunkirk DXL IO manual says about the economy feature on the boiler controller:

Economy Feature is factory set for 1 zone heating system.

To adjust, turn the ECONOMY dial D until the number displayed equals the number of heating zones.

The Economy Feature conserves fuel by reducing boiler temperature. If heating system is unable to supply needed heat to the house, Economy dial should be turned to lower setting (example: In a three zone house, turn dial to 2 or 1).

Conversely, if boiler provides adequate heat, added fuel savings can be achieved by selecting a higher setting (example: 4 or 5).

If heating and indirect water heater signals were not separated when wiring control, Economy Feature should be turned OFF to insure boiler supplies adequate temperature to heat the indirect tank.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-12-10 by Adam

Hello again. I checked all of the settings on my boiler (https://dunkirk.com/products/boilers-gas/dxl-series) and everything seemed to be functioning correctly. PSI hovered around 20, though. Then, I noticed it was set to "ECO", presumably to cut down on heating costs. When I switched this setting to "LO", and cranked up the thermostat, the radiator in question got hot. Perhaps the increased pressure pushed out an air pocket somewhere. In any case, problem solved! Thanks for the help.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-12-07 by (mod) - fix cold radiators that are air-bound or air-locked

Adam

As you were able to temporarily get the convector hot I suspect that the problem is

1- an air-bound heating water delivery pipe just ahead of the cold convector.

If there is air in the system, for example in a horizontal length of pipe that doesn't quickly or easily bleed to a nearby air bleeder, it can be difficult to get the air out of the system just by opening the bleed valves.

There are methods including using higher pressure (temporarily) to force water through the system and air out, sometimes using a pony pump.

Details are in these articles on how why and where air gets trapped in hot water heating systems, thus causing cold radiators, baseboards, or convectors:

AIR-BOUND HEATING SYSTEMS - home - start here

AIR BOUND RADIANT HEAT

AIR BOUND HEAT SYSTEM REPAIR by PUMP

AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

But before fooling with that procedure let's confirm that when you run the boiler up to full operating temperature, say 180F or 200 F max, the system pressure is sitting up close to 30 psi AND that you're not in a tall building with a boiler in the basement.

Too low boiler pressure can make it hard to push hot water to the highest convectors (if your cold one happens to be a high one) in the building.

I'll re-post a couple of your convector air bleeder photos here to encourage comments from other readers.

Keep us posted.
IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-12-07 by Adam

First let me say this site is amazing and incredibly helpful. Now I will ask my question :)

I have a heating system consisting of a boiler and a series of hot water convectors. They are National Art Convectors from National Radiator Company, all of them are working properly but one. Below is an image of what the radiator in question looks like. I bled all of them, including the non-functional one. It just doesn't get hot, even when all the others do.

I actually tried draining cold water out of the valve on the left (supply) side, and eventually the supply pipe got very hot. I then drained water out of the steam release valve and actually got the hot water coming across, but afterwards it just cooled down and stopped working again.

Album showing the radiator: https://imgur.com/a/jd0R2PZ

I've had a heating service contractor come check it out but they are stumped. The circulator is working properly, they tried adding water to the system, just won't get hot.

I inspected the air bleeder valve, and it looks like it may have two screws – one inside of the other. The inside one doesn't do anything when turned, which makes me suspect it is causing problems, but I have no idea. Any ideas on what to try next?

On 2018-11-25 by (mod) -

Right Wayne but depending on the piping distances and routing steam may not rise in the pipe to a steam radiator if that radiator is not venting.

On 2018-11-23 by Wayne

Thanks. I'll try that. Didn't sound like that to me as there was no heat to that radiator from the main pipe

On 2018-11-18 by (mod) -

Sounds now more like a bad steam vent. Try replacing it.

On 2018-11-18 1 by Wayne

Can you say more. Remember one radiator which wasn't working before the "flood" is now working, as are most of all the other radiators. How would you fix the last radiator. The main pipe below that radiator is cold but hot just a few feet away.

On 2018-11-18 by (mod) -

Ween,

If this is a steam heat system it sounds as if you flooded it.

On 2018-11-17 by Wayne

Let me add to the other comment. I recently left the water running (a trickle) when I filled the system. When I returned from work I had a flood from leaking radiators

. I drained the system down to the normal level and some radiators that were not working before are now working. This end of the run radiator that I speak of, I am not sure whether is was working before or not, but others tell me it was not working. I have to admit, a few years ago I left the water running causing the same flooding problem.

Maybe that last radiator hasn't been working since then. Like I said, the radiator next in line (about seven feet away) is working and the main pipe to the last radiator is cold.

On 2018-11-17 by Wayne

We have a steam radiator system. An end of the run radiator stays cold. I felt the main pipe below the radiator and it was cold. The radiator before this in line is hot. I do not understand the main pipe being cold to this last radiator.

On 2018-10-01 by (mod) - how do we know if a radiator or hot water heating pipe air vent is working?

Thanks for a good question, Doug. Indeed it's not obvious how we know if the air vent is working or not.

If an air vent does not work on a hot water or steam radiator ultimately the radiator won't get hot when the thermostat is calling for heat, because air trapped in the radiator will prevent hot water or steam from entering it.

If the radiator does not get hot, the radiator or the piping feeding it may be air-bound.

If the radiator does get hot on a call for heat from that heating zone then it is not air bound.

If your system uses steam heat then at every heat-on cycle you will hear air escaping the steam vent as the radiator heats up.

For manually-operated air vents on hot water radiators, if you open the vent and water squirts out the vent is working and the radiator is not air bound.

Those vents are detailed at AIR BLEEDER VALVES

For a complete review of this topic see

AIR-BOUND HEATING SYSTEMS - home

On 2018-10-01 by Doug

How can u tell radiator air vent is malfunctioning.

On 2018-01-16 by (mod) -

Yes indeed, George. Replacement radiator valves are sold by plumbing and heating suppliers

On 2018-01-15 by George

Can you replace a shut off radiator valve stem washer and where could you purchase

On 2017-12-20 by (mod) -

Thank you for the discussion, Chris. Working together helps us both.

On 2017-12-19 by Chris

Many thanks again for your competent answer and useful information. I have checked the website you kindly provided me with.

After some more investigations it occurred that Danfoss TRV Kv is 0.9 and that of a two-way BV is ca 23 – 26. Thus, the answer of my query is “crystal clear”, namely either to use BV, or to keep TRV, but after removing (if possible) the Kv nozzle….

The latter will allow using the TS head for setting the temperature which could be better than doing that with BV because, as it is written, BVs work fine in either fully closed or fully open position, but not in some intermediate, where problems with the gasket can occur. I do appreciate your time and efforts taken in considering my case and clarifying it in the best manner. Thanks. Best. Chris

On 2017-12-16 by (mod) - troubleshooting TRVs = Thermostatic Radiator Valves

Chris

Gee that's a very expensive globe valve. IN that case you may as well replace the TRV with a BV just as you suggested.

My OPINION is that a fully open BV with no reduced diameter will provide both the least flow restriction and the most flow-through. The Bernoulli effect achieved by a venturi design can create a lower pressure behind the venturi but I think the available water flow to that point is not going to be increased. To get beyond arm-waving speculation would be an interesting question to ask of a heating or fluid dynamics engineer.

Can a Kv venturi at a rad valve provide a net gain in hot water flow-through where there remains the constriction of the thermostatic valve (TR) interior?

See this interesting technical analysis

http://www.hydroteam.gr/userfiles/products/TA_Handbook_3_eng_1580016466.pdf

You could, as a simpler and most-likely less costly approach (where there are multiple radiators involved) look at changing out the hot water circulator pump in the system to install a variable speed model that would let you try driving the hot water piping loop at a faster rate. That will deliver more BTUs to the same radiator, and I suspect would be more effective than a Kv nozzle / TRV combination.

On 2017-12-15 by Chris

Many thanks for your prompt response. The case is that I have to use the thermostatic radiator valves (TRVs) always fully-open (the thermo-head removed) in order to get maximum possible temperature.

Actually, they do not act as a real TRV, but as globe valves. Since I cannot control parameters like temperature of incoming hot water, its pressure, etc. the only way is to replace the TRV with a ball valve (BV) considering that the latter in fully-open position does not create any “resistance” to the water flow since the diameter of the ball’s hole is the same as the pipe diameter, say 1/2".

As per my understanding, the geometry of the TRV influences some how the flow, requiring it to go in an Z-pattern and because of that the volume of the water passing through the valve, say for a minute, will be less than the one passing through a BV.

From the other side, as I mentioned, the TRV has a Kv nozzle that might improve the way the water enters the radiator and so compensate the smaller water volume compared to that in case of the BV. Thus the query is which valve (TRV or BV) will be more effective in fully-open position. Thank you for considering the issue and providing your advice.

On 2017-12-13 by (mod) -

Chris

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.

On 2017-12-13 by Chris (komart@hotmail.com)

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

Chris

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 K_v - The K_v-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. K_v 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.

See

Boysen, Herman, K_v: What, WHy, How, Whence?, [PDF] Danfoss, (2011) retrieved 2017/12/12 original source: http://heating.danfoss.com/PCMPDF/VFHBG202_kv.pdf

On 2017-12-13 by Chris (komart@hotmail.com)

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

Sabina,

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.

Generally higher numbers mean more heat, lower numbers mean "gimme less heat"

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 too hot just turn the valve clockwise, to a smaller number.

If your radiator is cold, and provided the valve on the radiator is open, 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 inspectApedia.com on-Page search box to find out article series

on AIR-BOUND HEATING SYSTEMS

(Also found in ARTICLE INDEX 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 by (mod) - replacing a full size radiator in a steam system with cast iron base.

Ron,

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 by (mod) -

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

On 2017-03-09 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 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 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 by (mod) -

Jill:

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 by (mod) -

Nicci

We repeat your question and give a detailed step by step reply near the bottom of our article on radiator air bleeder valves: https://inspectapedia.com/heat/Air_Bleeder_Valves.php

On 2016-10-27 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 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 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 by Alfredo

My steam radiator bleeding air with bubble what can I do

...

Continue reading at RADIATOR VALVES & HEAT CONTROLS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR-BOUND HEATING SYSTEMS - home
• AIR BLEEDER VALVES - home
• COLD HOT WATER RADIATOR or BASEBOARD
• COLD STEAM HEAT RADIATORS
• RADIATOR VALVES & HEAT CONTROLS
  • RADIATOR VALVE ADJUSTMENT - How to Adjust or Control the Level of Heat From Radiators
  • AUTOMATIC RADIATOR VALVES - Automatic or Thermostatically Controlled Radiator Valves
  • RADIATOR CONTROL VALVES on CONVECTOR HEATERS
  • RADIATOR VALVES MANUAL - Which way to turn the radiator valve
  • RADIATOR VALVE STUCK or BROKEN REPAIR - how to repair or replace radiator valves
  • RADIATOR VALVE TYPES - what's the difference?
  • STEAM HEAT VENT CHOICES & INSTALLATION - Adjustable or Thermostatically Controlled
  • STEAM VENTS THERMOSTATICALLY CONTROLLED - Used to control steam radiators
• STEAM RADIATOR PIPING CONNECTIONS

Suggested citation for this web page

RADIATOR VALVE & HEAT CONTROL FAQs-2 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 HEATING RADIATORS

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