Ceiling mounted heating radiator (C) Carson Dunlop Associates How to Diagnose & Fix Cold Radiators, Baseboards & Convectors - hot water heat

  • COLD HOT WATER RADIATOR or BASEBOARD - CONTENTS: How to fix a cold radiator or baseboard - No Heat? What to check first on a hot water (hydronic) heating system.
    • How to bleed air out of a radiator. How to identify, inspect, diagnose, and repair problems with hot water or steam radiators, baseboards, or heating convectors. How to inspect, diagnose, and repair problems with steam radiators. If your radiator or baseboard is cold and the heating system is "on" - here we diagnose the problem. Where leaks occur on hot water and steam radiators, convectors, and baseboards
  • POST a QUESTION or READ FAQs about troubleshooting cold radiators, convectors, baseboards on hot water heating systems

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Troubleshoot cold radiators, baseboards, convectors in hot water heating systems: this article describes the diagnosis & repair of cold "hot water" heating baseboards, convectors, radiators, or "hot water" radiators. We provide articles that help in diagnosing and repairing no-heat problems with each types of hot water or steam or fan convector heat delivery systems.

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What to Check First if your Radiator, Baseboard, or Convector is Not Getting Hot

Radiator air bleed valve (C) Carson Dunlop Associates

First let's be sure we're reading the best cold-radiator diagnostic advice for your situation.

This article will help you fix a hot water heating system (hydronic) radiator that is not heating up as it should.

If your heating system runs on hot water (it's a hydronic heating system) but it uses those skinny horizontal baseboards instead of radiators, you will be happier if you
see BASEBOARD HEAT for cold baseboard diagnosis and repair.

If 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.

[Click to enlarge any image]

Our page top heating system illustration and the sketch at left were provided compliments of Carson Dunlop Associates.

If none of your heating radiators, baseboards, etc. are getting hot, start your diagnosis of the problem at NO HEAT - BOILER / FURNACE DIAGNOSIS. It may be that your boiler is simply not running, has lost power, is switched off, or that the thermostat is not calling for heat.

If you have heat in some areas but not others we discuss diagnosing baseboard heat problems below, followed by a discussion of radiators and convector unit problems for both hot water and steam heat.

Guide to Diagnosing Cold Hydronic (hot water) Radiators in buildings

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".

In the "cold radiator" diagnosis article below 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. See details

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 they have been left "on" - 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.]

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.

Thermostatically controlled radiator valves:

Thermostatically controlled hot water radiator valve (C) Daniel Friedman

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, such as the automatic radiator valve shown at above left.

This (more expensive) radiator control valve lets you treat each individual radiator as a "heating zone". As long as the thermostat is calling for heat, each radiator can be regulated automatically.

Hot water heating radiator (C) Daniel Friedman Radiator valve with air bleeder (C) Daniel Friedman

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 (turned counter-clockwise - the red circle in our photo at left) then you may need to bleed air out of the radiator so that hot water from the boiler can flow into the radiator. Many hot radiators have an air bleeder valve (blule circle in our photo at above left) that the homeowner can operate if she takes care about scalding risks and avoids making a mess by bleeding just air, not water.

In our photo at above right you can see not only the radiator control valve, but more: we can conclude that this is a hot water heating system, not a steam heat system because there is no automagic air vent that we find on steam radiators, and second, the radiator control valve includes an air bleeder - that nut on the side of the valve body (blue arrow, photo above right).

In looking for an air bleeder in our article on this procedure
at BLEEDER VALVES it's easy to miss this particular air bleeding device.

Watch out: even if the radiator valve appears to be "open" - that is, turned fully counter-clockwise (red circle in the photo at above left), if the valve is broken internally you may be just turning the knob but the valve may be staying closed inside.

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.

Heating convector control valve (C) Daniel FriedmanOn a heating convector unit there is usually an individual hot water flow control 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.

Unlike 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.

Note that a hot water heating convector will also usually have its own personal air bleeder valve too - typically at the opposite end of the convector from the water feed valve.

How to Bleed Radiators of Trapped Air

Radiator air bleed valve (C) Carson Dunlop AssociatesIf just some of your hot water radiators are not getting hot you may just need to bleed or remove air from the "cold" hot water radiator, baseboard, or heating convector unit,

Carson Dunlop's sketch (left) shows a common location for the air bleed valve on a cast iron radiator.

The advice to leave this valve alone is intended for home inspectors who don't want to risk spilling water on someone's floor or opening a valve to find that they can't close it again.

See AIR BLEEDER VALVES for details about how to get an individual cold radiator working again if it's air bound, and
see AIRBOUND HEAT SYSTEM REPAIR if the cold radiator, convector, or baseboard problem seems to affect all of the heating radiation devices on all or part of an individual heating piping loop or zone.

Since on many hot water heating systems a key air bleeding or air vent point is at the air scoop or air separator closer to the boiler,

Hot water heating boilers, their inspection, diagnosis, and repair are discussed beginning

Guide to Fixing Cold Steam Radiators: Steam Vents & Radiator Slope

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

Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat.

Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally. A steam boiler will usually turn on right away in response to the thermostat being turned up or on a call for heat.

Make sure that the control valve at the heating radiator is "open" or "on" as we describe just below. Details are

First check the radiator valve.
At Guide to Diagnosing Cold Radiators in buildings we illustrated different types of heating radiator control valves and explained their operation.

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. Here is diagnostic and repair advice.

If some of your steam heat radiators are not getting hot, the steam vent may not be working.

Steam vent on a radiator (C) Daniel Friedman

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.

When steam is first rising in the heating system, the steam heating radiator will be cool as will be the steam vent.

The vent opens, allowing rising steam to enter the radiator by pushing air out through the vent.

When the steam radiator and steam vent are warm or hot, the vent closes. If a steam vent stops working, rising steam cannot enter the radiator and it will be slow to heat or may not heat at all.


also STEAM HEATING SYSTEMS for details.

Steam radiator sloped the wrong way - steam condensate blockage

Steam radiator slope (C) Carson Dunlop AssociatesAs our Carson Dunlop sketch shows (below, left), steam radiators can be sensitive to exactly how they are installed and pitched or sloped.

You'll want to learn if your steam heating system is a "one pipe" or a "two pipe" design, but in either case, if the steam supply or condensate return piping have been moved or settled so as to have lost the proper slope, correcting those conditions may be needed.

[Click to enlarge any image]

That's because condensate, produced by cooling steam in the radiator, has to be able to drain back out of the radiator.

A steam radiator that is sloped the wrong way, perhaps due to building floor settlement or a change made by an inexperienced remodeler, will become partly or even completely blocked by accumulated condensate, leading to loss of heat.

This article series answers most questions about all types of heating systems and gives important inspection, safety, and repair advice.


Continue reading at AIRBOUND HEAT SYSTEM REPAIR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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