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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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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.
If 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
at RADIATOR VALVES & HEAT CONTROLS.
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.
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.
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.
See AIRBOUND HEAT SYSTEM REPAIR
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.
On 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.
If 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,
see AIR BLEEDER VALVES.
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,
see AIR SCOOPS SEPARATORS PURGERS.
Hot water heating boilers, their inspection, diagnosis, and repair are discussed beginning
at BOILERS, HEATING.
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. 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
at RADIATOR VALVES & HEAT CONTROLS.
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.
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.
See STEAM VENTS and
also STEAM HEATING SYSTEMS for details.
Steam radiator sloped the wrong way - steam condensate blockage
As 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.
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
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(Dec 17, 2012) Chuck Arkle said:
How do you get heat from a steam radiator using hot water in and out of the bottom of the radiator? The supply should come in the bottom and the return out the top with a bleed on each radiator or the use of a Spiro vent or similar vent device installed in the return at the boiler in the return in accordance with the vent manufacturers recommendations.
Steam radiators are heated by steam, not hot water. It's condensate returning from that bottom outlet.
(Jan 13, 2013) Carla said:
I live on the second floor of a two-story house and I'm having heating issues. I have natural gas powered, cast-iron steam radiators. The two radiator's in my living room (where the thermostat is located) will not heat up during normal operation, i.e., leaving the thermostat set at a constant temperature and the thermostat is calling for heat. When the boiler runs, the radiator's on the other side of the house (bathroom & bedroom) will heat up. The radiator in the bedroom heats up partially and the one in the bathroom, fully, and the two in the living room not at all but you can hear the air hissing. The only time the two in the living room will heat up is when the thermostat is turned up really high, like if it's set at 68 degrees then turned up to 80 degrees, then they'll put out heat. Is this normal?
Additional info: Landlord came yesterday and turned the boiler up from 3 psi to 3.5 psi (should work at 2 psi or less); told me to leave the supply valve in the bedroom only partially open and that it can't be closed completely because it's going bad (I opened it fully after he left); there's also no insulation on the pipes and you can hear hammering in the pipes when the boiler runs.
I hope I explained the situation well... thanks in advance! Forgot to mention... hot water will run out at the end of a shower even when no other hot water has been run... relevant?
(Jan 25, 2013) Vik said:
I have a Thermolec electric boiler to heat a duplex (2 stories). I have heat on the upper floor but none in the basement. The boiler operates in a weird manner. I am not certain whether the pump is working or not, however the water heating cycle comes on and off every two minutes, which means that the thermometer starts from 60 C to 80 C within 30 seconds, then cools off till it is back to 60 C and it restarts. My neighbor's boiler takes a full 12-15 minutes to do the same cycle. Do I have air in the system, is my pump not working (although I have very high heat on both ends of it),. What could my problem be?
(Jan 27, 2014) Kevin Clennan said:
We have a 2 zone baseboard hot water heating system. The 1st zone going to the down stairs works good. The 2nd zone going to the up stairs has 6 base boards and 3 are working and 3 are not. They each have there own bleeder valve on them and when I went to bleed off one of them I got just a little air and then nothing. No water came out either. even when its not calling for heat shouldn't there be water coming out of the bleeders when opened or is that normal to have no pressure when not calling for heat.
Presuming that in the second zone we are sure that all 6 baseboards are on a single pipe run - that is there are no intermediate valves or controls that might have split the zone into two sub-loops of 3 baseboards each, I would look for
1. a clogged bleeder valve - debris may have blocked air exiting from the bleeder valve when you tried to open it.
2. low system pressure; because most circulator pumps do not have much lift or push capacity, they depend on two conditions to be able to circulate hot water through the upper floor zones:
2.1. sufficient heating system pressure to overcome the head pressure of water in pipes going to upper floors
2.2. no air in the piping system (which you know since you're trying to bleed air out)
If you search InspectApedia for the article titled
PRESSURE & TEMPERATURE SETTINGS, CONTROLS
you'll get more help.
Also search for AIR-BOUND HEATING SYSTEMS to see methods used to force air out of a partly air-bound system.
(Jan 27, 2014) Roni said:
Have an Ultimate oil burner/boiler ( DHW coil removed), with 4 zones.
1st zone main floor
2nd zone upstairs
3rd zone sunroom addition
4th zone Amtrol indirect HW maker
2nd zone piping freezes up with cold weather (usually below 20F). Thermostat in master br must be kept at 59-60F otherwise other two bdr's get way too hot.(poorly designed loops for the pipes, too $$ to fix)
Is there a way to add a recirculating pump to keep a small flow of HW moving thru the 2nd zone even when the zone isn't "officially" calling for heat? Kinda like the idea where a pump is added to the furthest HW faucet in a home that keeps HW flowing so there's no need to run the water forever to finally have the HW reach the faucet...
Only other way to describe it would be for the 2nd zone valve to have variable flow-trickle to prevent pipe freeze and fully open when stat calls for heat. Crazy idea? Impossible solution?
Yes there are several solutions:
1. immediately pending other steps, keep the temperature high enough to avoid freezing - in your case 60F
2. loveuming that your system runs with a single circulator and multiple zone valves, you can have your heating tech wire the circulator to run continuously - this is how homes in Canada are usually heated; it's custom in the U.S. to have the thermostat call for heat by turning on the circulator and the boiler temperature turn on the boiler via the aquastat. But in Canada the circs run all during the heating season (at least on many systems) and the TT is wired to turn on the heating boiler.
3. You could install a variable speed circulator for the above application (see extra notes at 4. below)
4. you could install a booster or extra circulator just on the freeze-prone zone. In this arrangement you would think you'd want to latch open the zone valve manually so that the circ could push water around, but you may have to also change the zone valve wiring to NOT call for heat - otherwise when the zone valve is manually latched open, its internal end-switch will also turn on the main circulator.
In other words, you can convert the problem zone to one that is always circulating. If you install a variable speed circulator you can circulate water more slowly through that zone (or all zones) continuously. When the boiler temperature drops below the cut-in the boiler will cycle and provide heat.
Alternatively if you disconnected the trouble zone's zone valve end switch wires (that normally turn on the main circulator), then latch the zone open, then add an additional variable speed circulator just for that zone, you'll circulate water more slowly.
This is slightly garbled as I'm typing off the cuff - if the ideas are not clear, ask again.
To find variable speed circulators search InspectApedia for that term or search for the article title
Guide to Circulator Pump Relays & Other Controls for Heating System Circulator Pumps
(Jan 30, 2014) Mz diva said:
My radiator does not have a knob to turn it off and on. We bled it to release air. It still is not getting hot, only warm. Any suggestions?
You may need to bleed more air - open the air bleeder until you begin seeing water coming out of the valve, then shut it off.
If that does not fix the problem the heat piping itself may be air-bound elsewhere in the system, or a valve partly closed.
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