Radiator control valve (C) Daniel Friedman Radiator Valves & Vent Controls
Hot Water & Steam Heat Control Guide

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Radiator valve inspection & troubleshooting:

Here we explain 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.

Which way to turn the radiator valve to open or close it. How to replace a leaky or stuck heating radiator valve. Install a thermostatically operated radiator valve.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Guide to Using, Adjusting, Diagnosing & Fixing or Replacing Hot Water or Steam Radiator Control Valves & Vents

Two Pipe steam radiator (C) Daniel Friedman

Article Contents

Traditional "Manual" Radiator Valves

Radiator valves are opened to allow hot water or steam to enter and heat a radiator, or closed to turn off or reduce heat output from the radiator. By "manual" radiator valve we mean that you have to turn the valve open or shut yourself. We discuss automatic (thermostatically controlled radiator valves and other radiator controls below.

At above left is a top-fed two pipe steam radiator at Google Headquarters in New York City.

If your heating system radiators won't get hot, for hot water radiators or convector heat, see COLD HOT WATER BASEBOARD / RADIATOR;

For cold steam heat radiators see COLD STEAM HEAT RADIATORS for help in diagnosing the problem.

If your heat is provided by baseboards there will not normally be individual shutoff valves at those devices, but if your system uses one circulator and provides multiple heating zones (and thermostats) there will be zone control valves (usually near the boiler) that are opened or closed by the room thermostat(s).

Cold heating baseboards are discussed at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE.

Which Way to Turn the Radiator Valve

Radiator control valve (C) Daniel FriedmanIf your heat is provided by individual hot water radiators or convector units, usually there is a control valve at each radiator or convector. Make sure that the control valve at the heating radiator is "open" or "on". Usually turning a radiator valve "clockwise" or "down" closes the valve (turns the heat

At COLD HOT WATER BASEBOARD / RADIATOR we include links to additional detailed articles that will help you correct a problem with heating baseboards or radiators that are not working:

Check the radiator control valve: If a radiator is not getting hot: (steam or hot water) first see if the valve that controls it has been turned off. Try turning the valve counter-clockwise to see if it will open.

In our photo (left), the heating convector control valve was found at floor-level under the heating convector. The "open" and "close" directions for this "radiator valve" were nicely marked by the manufacturer (click to enlarge the photo).

If the radiator valve does not turn in that direction, try turning it in the other direction (clockwise or "closed") to see if the radiator valve is stuck. You may also find the same control valve at heating convectors (but not usually at heating baseboards).

While people sometimes turn off radiators in an un-used portion of a building we usually find that most radiator valves have been left in the "on" position - in fact turning off a hot radiator in some building areas could lead to its freezing and cracking.

Steam radiators, on the other hand, can usually be turned-off with impunity since steam radiators do not normally contain water in its liquid form. [That's true at least so long as condensate has not become trapped inside of the steam radiator.]

How to Fix Stuck Heating Radiator Valves

Watch out: don't use excessive force to try to turn a "stuck" radiator valve. First, you may be trying to open a valve that is already in its fully-open position. Second, the valve may actually be jammed. Excessive force can break the valve or even cause a leak. If the valve won't turn at all counter-clockwise towards "open", try turning it the other way - clockwise, towards "closed". If the valve now turns you'll know it was already in its open position.

Broken Radiator Valves

Watch out: even if the radiator valve appears to be "open" - that is, turned fully counter-clockwise, if the radiator valve stem is broken internally you may be just turning the knob but the valve may be staying closed inside.

If your radiator valve turns too easily or if it does not appear to raise (opening) or lower (closing) when turning, and especially if turning the valve makes no difference in the behavior of the radiator, the valve stem may be broken. (First check for air bound radiators or if your heating system uses steam, check for a steam vent that is not opening.)

Usually while turning a radiator valve to from "closed" to "open" position, if you look closely at the valve stem - the metal rod or shaft extending below the knob you are holding, and extending into the body of the valve itself - you'll see that as you "open" the valve the stem gets "longer" and often a less-oxidized, shiner part of the valve will become exposed as it moves upwards from having been inside the valve body.

That's a great way to convince yourself that yes, the valve is probably opening internally too, you're not just turning the knob. If the valve body has broken loose from the valve stem, that's an internal problem you can't see, but turning the radiator valve knob, even if it rotates, will not open a broken, stuck, frozen valve.

If only some of your hot water radiators, hot water heating convector units, or hot water baseboard heating sections are not getting hot and the radiator valve is open,
see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE (hot water heat) or if a steam radiator valve is open but the radiator is still cold, the steam vent may not be working.


also STEAM HEATING SYSTEMS for details.

Types of Radiator Valves: Hot Water vs Steam

Hot Water Heat Radiator Valves

Radiator valve with air bleeder (C) Daniel Friedman

In our photo at left you can see not only the radiator control valve, but lots more information:

This radiator is being fed from the top. We know that this must be either a hot water radiator or a two pipe steam heat radiator.

Now look closely at that air bleeder connector on the side of the radiator valve.

From this detail we can conclude that this is a hot water heating system, not a steam heat system

Hot water can enter a hot water (hydronic) heating radiator at the radiator top or bottom. Hot water radiators may have an air bleeder valve but never a steam vent valve.

Steam can enter a steam heating radiator at the radiator top too (most but possibly not all two pipe steam heat systems) or also at the radiator bottom (one pipe steam heat systems).


Steam Radiator Control Valves

Radiator control valve (C) Daniel FriedmanIf your heating system uses steam radiators or steam convectors see  COLD STEAM HEAT RADIATORS for help in diagnosing and fixing steam radiators that won't get hot. Excerpts from that article are found below.


First check the radiator valve. It's standard to ask first "is the radiator valve turned on or "open" (fully counter-clockwise)?

But other problems can cause a steam heat radiator to stay cold when you want heat.

If a steam radiator valve is open but the radiator is still cold, the steam vent may not be working.

Our photo (above right) shows a typical steam radiator vent.

See STEAM RADIATOR PIPING CONNECTIONS for an explanation of different types of steam piping and steam-radiator piping connections.

Also see STEAM VENTS and


Reader Question: where do steam pipes enter steam radiators: top, bottom, or both?

Two pipe steam radiator (C) Daniel FriedmanI had a question about the article at RADIATOR VALVES & HEAT CONTROLS.

I’m looking at the sub-section “Types of Radiator Valves: Hot Water vs. Steam” ...

Photo at left: two pipe steam radiator fed from top right end. [Click to enlarge any image]

I was trying to make sense of what was written - it must be hard to describe these hot water and steam heating systems. In some cases it seems that in fact steam DOES often enter a radiator at the top.

At this point I am just lost. We don’t have many residential systems with radiator systems (steam or hot water) so I am trying to educate myself but don’t have anything in front of me to compare what I think I understand.

Kind Regards, -Doug

Reply: Up-feed - Down-feed, One-pipe - Two-Pipe Steam Piping & Radiators - What's the Difference?

Two Pipe steam radiator (C) Daniel FriedmanDoug, the other page (not at InspectApedia) that you gave provides information from Dan Holihan - probably the most-expert fellow alive when it comes to steam heating systems. Dan's text includes these two statements:

Older steam radiators have nipples across just the bottom portion of the sections. This is because steam is lighter than air. When the steam enters the bottom of a radiator (as it always will in a one-pipe steam radiator), it flows upward into the sections, displacing the air as it goes.

Two-pipe steam systems usually have the steam entering through a pipe at the top of the radiator. [1]

Dan is right again. Most two-pipe steam heat systems will show up with the steam entering the radiator at one end at the radiator top (below left), and the condensate return will exit at the bottom of the radiator at its opposite end. [1][12][16][17]

All one pipe steam radiators are fed with a pipe connection to the bottom of the radiator.

In response to your question we have added an article to help clarify the different types of steam heat piping - to - radiator connections and where valves will occur.


Hidden Manual Radiator Control Valves on Heating Convectors

On a heating convector unit there is usually an individual valve that lets the unit be turned down or off - but as our photo (left) shows, the valve can be a little harder to spot.

Heating convector control valve (C) Daniel FriedmanUnlike a radiator valve, a heating convector control valve may be hidden by the convector's steel cover, or it may be little and hard to recognize as we show here.

This valve, if it's not jammed by corrosion, is operated by a screw driver; it may be possible to get this valve working by gently loosening the lock-nut and then turning the control screw with a flat-bladed screwdriver.

Do not take apart this valve while the heating system is on and hot - you risk getting sprayed with hot water or you may start a leak that's hard to stop without making a mess and having to shut down the whole heating system.




How to Adjust or Control the Level of Heat From Radiators

Manually Setting the Radiator Valve

On hot water heating systems and two-pipe steam radiator heating systems you can adjust the radiator valve to:

If your hot water radiator is too hot or the room is too hot, you can partially-close the radiator valve.

If your hot water radiator is too cold, be sure that the valve is open and that the radiator is not air bound.


If your steam radiator is too cold be sure that its supply valve is open. If it's a one pipe steam heat system (only one pipe comes to each radiator), be sure that the steam vent is working (you should hear it hissing when steam is rising in the system).


If you steam radiator is too hot in a two-pipe steam system, according to the U.S. DOE,

In two-pipe systems, older steam traps often stick in either the open or closed position, throwing off the balance in the system

. If you seem to have problems with some radiators providing too much heat and others providing too little, this might be the cause. The best approach is often to simply replace all the steam traps in the system.

If your steam heating system pipes are noisy see BANGING HEATING PIPES RADIATORS wHere we explain steam condensate return problems that can cause banging clanging pipes.

There are additional methods for automatically controlling the heat output from individual heating radiators, for both steam and hot water heat: thermostatically controlled radiator valves and adjustable or thermostatically controlled steam vents. We discuss these controls beginning at AUTOMATIC or Thermostatically Controlled Radiator Valves - TRVs.

Reader Question: how to turn off un-wanted heat at a baseboard or radiator

Cast iron baseboard from Baseray - see U.S. Boiler Company, (C) InspectApedia12/31/2014 Margaret said:

My husband and I just bought a 1948 built house and we think it has all original heaters. 2 rooms have the stand up style cast iron radiators.

Our kitchen, dining, and bedroom have what we think are cast iron baseboard style heaters. They look a lot like, but are not exactly, the ones pictured here.

[Click to enlarge any image]

All of the above-mentioned rooms are all on the same heating zone. My question is, how do I shut off heat to only one of the rooms? I'd like to completely shut off the heat to my bedroom only. Can I safely do this without shutting off the heat to the other rooms?

How do I find the valve to shut this room off?

At this point the bedroom is our biggest waste of heat as we have to keep a window open in there to keep it from being insufferably hot, while the other rooms in that zone are still quite chilly. We have the thermostat set down to 50.
Please help!

Reply: comparing baseboards & radiators: which ones have shut-off valves?

Cast iron heating radiator (C) Daniel FriedmanMargo

You can shut off heat to individual heating radiators such as the cast iron radiator shown at left by closing the individual radiator valve or by installing a thermostatically operated radiator valve such as those we illustrate just below.

But your "radiators", if the photo you refer-to at above-left is correct, is a segment of cast iron baseboard. I know the terms are confusing but "baseboard" is generally a horizontal heating element placed (usually) close to the floor.

Three cases of heating baseboard section control

1. Heating baseboard sections piped in series in one loop of hot water piping: In the most common heating baseboard design one cannot close off an individual section of baseboard type "radiator" because it is piped in series with the rest of that heating zone.

Cutting off that baseboard by installing a shutoff valve would stop hot heating water from passing on to other baseboard sections in that zone. Instead you'd have to shut off all of the heat that shares that hot water piping loop.

If your baseboard heat was installed as an individual heating zone serving the rooms you name, it is probably operating as a heating zone, controlled by a thermostat and zone valve. See ZONE VALVES, HEATING.

You'd have to have a plumber modify the heating system piping to create individual zones - technically possible but, depending on the ease of access to piping below the rooms involved, possibly rather expensive.

2. Heating baseboard installed to replace older radiators: If the cast iron baseboard heating sections were added to replace older stand-up radiators such as the heating device we show at left, then possibly the piping included a shut-off valve at the inlet end of the baseboard section or in the basement or ceiling below that location.

3. Heating baseboards piped in parallel: Rarely we find sections of heating baseboard piped in parallel. In that case individual sections of baseboard might have a shut-off valve installed at the inlet end of the baseboard. But as it's rare I doubt that you'll find a shut-off valve for your heating baseboard.

Automatic or Thermostatically Controlled Radiator Valves - TRVs

Armstrong thermostatically operated steam vent (C) Armstrong International

The radiator control valve opens or shuts to allow hot water or steam to enter and heat the radiator. An automatic or thermostatically controlled radiator valve allows you to set the desired room temperature.

The automatic hot water or steam radiator valve, thermostatically controlled, will automagically open or close to attempt to control room temperature to the desired level.

Keep in mind that with any heat control installed right at the radiator, the control will be sensing temperature in that location, not across the room, so some experimenting to find the best setting will be needed.

Armstrong Corp. provides the RV-4 One-Pipe Steam Radiator Valve that operates as a room thermostat suitable for residential low-pressure steam heating systems. By installing a thermostatically controlled steam vent at each radiator, every radiator can be controlled or set to the desired temperature.

There is a central advantage of thermostatically operated steam vents over swapping out the actual radiator control valve for a thermostatically controlled radiator valve, that is, they are easier and less disruptive to control.

The original steam vent is simply unscrewed and the new thermostatically controllable steam vent is screwed in at the same location.

Watch out: it's safer to install or change steam heating system parts when the system is not calling for heat and when the steam boiler and radiators are cold. Don't be fooled. If your heating system is on and the steam boiler is hot, unscrewing the steam vent on a "cold" steam radiator will allow steam to rise into the radiator (forcing air out of the steam vent opening) and you could be seriously burned by rising steam.

Thermostatically controlled hot water radiator valve (C) Daniel Friedman

Replacing Manual Radiator Valves with Thermostatically Controlled Radiator Valves

If you have to replace the control valve on a hot water or steam radiator or convector unit, consider installing a new valve that incorporates a thermostat as well.

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.

This (more expensive) radiator control valve lets you treat each individual radiator as a "heating zone".

As long as the room thermostat is calling for heat, each radiator can be regulated automatically when a thermostatic radiator valve (TRV) is installed..

References, Sources, Installation Manuals for Thermostatically-controlled Radiator Valves

Automatic or Thermostatically Controlled Steam Vents

This topic has been moved and consolidated at STEAM VENTS - home, where we discuss other steam vent problems such as spitting water, clogging, steam valves that do not open or close when they should, etc.

At STEAM VENT TYPES, SELECTION we identify the different types of steam vents use on 1 pipe and 2 pipe steam systems.

Choosing & Installing Adjustable or Thermostatically Controlled Steam Vents to Control Steam Heat


Watch out: If the radiator continually makes noises (whistling or wheezing) at the steam vent, there is a problem that needs to be fixed: a bad steam vent, steam piping problem, steam pressure set too high, or boiler oversized for the heating distribution system.

Watch out: to be sure your steam heating system and its controls are properly adjusted excessive steam pressure can be dangerous.

Reader comments:

(Nov 7, 2012) Anonymous said:

Great articles here. Very informative.

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


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