Air-bound heating baseboard or radiator repairs:
Here we explain how to remove un-wanted, air from noisy or air-bound hot water heating system pipes, radiators, convectors, and baseboards using the automatic water feed valve on a heating boiler.
If a hot water heating system develops too much air in the piping you may hear bubbling or gurgling in the heating pipes when the heating system is operating, or worse, so much air may be in the heating piping, radiators, or baseboards that heat may simply not circulate at all.
If necessary there are additional methods used to remove air from air-bound hot water heating systems using two different service procedures to force air out of airbound pipes in a hot water heating system.
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If some heating radiators or some sections of heating baseboards of your building are not getting hot, or if your building circulator pump runs continuously but heat is not being delivered to the heating zone served by that circulator, the discussion beginning
at AIR BLEEDER VALVES (just bleed air out of the system) and continuing here (how to forcer air out of the system) can help diagnose and cure that problem.
If you cannot bleed out un-wanted air and if using the water feed valve method described here do not work, you'll need to
see AIR BOUND HEAT SYSTEM REPAIR by PUMP.
Readers should also see DIAGNOSE OIL HEST NOISES for diagnosis and repair of other heating system noises on both oil and gas fired heating equipment. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
If your heating system is not working properly, see NO HEAT - BOILER or NO HEAT - FURNACE. This article series answers nearly all questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Here’s the problem, I have a one pump three zone hot water baseboard heating system. The circulating pump keeps running even though there is not call for heat. This happens even in the summer, so I just shut the emergency switch off, but now, it’s getting cold and I want to turn the system on. One of the zones does not get heat, so I replaced the TACO zone valve head thinking that was the problem.
Well, the pump is still running, and no heat even when the thermostat is set to 90. The furnace does not fire up either. I plan on eliminating the thermostat to see if the furnace would turn on by touching the two wires together, but saw your email and decided to write to you first.
The other two zones do heat up when heat is called. This is an American Standard system that was installed new in 1960. The pump has been changed a few times over the years. Any suggestions? - anonymous, Union NJ
Your heating system baseboard, hot water piping, or one or more radiators may have become airbound if:
Your thermostat for the heating zone(s) involved is calling for heat, the boiler is hot, the circulator pump is running, but all or part of the heating zone served by that circulator pump is not getting hot. More than one problem could cause this symptom but below we list possible causes in order of probability:
In this article we explain how to locate, inspect, diagnose problems with, use, or replace automatic and manual air bleed valves on hot water heat, and we explain methods used to remove air from air-bound hot water heating systems by finding and repairing or using automatic or manual air bleeder valves, or by using two different service procedures to force air out of air bound pipes in a hot water heating system. This article is divided into these main sections:
Here we describe the procedure that a heating service technician may use to remove un-wanted air in a hot water heating system in order to correct noisy gurgling pipes or to correct loss of heat due to an air-bound radiator, heating convector, or section of hot water heating baseboard.
If your hot water heating system has become air-bound (one or more sections of heating radiators or baseboards are staying cold even though the boiler is on and the circulator pump is running), and if your system does not have an air bleed valve to remove air blocking water flow, you probably need to call a heating service technician who will use one of the methods we describe here.
If your heating system does include both automatic and manual air-bleeder valves it is possible that you can correct a noisy or airbound heating system yourself.
We use this procedure to remove air blocking heating water flow through baseboards or radiators when there is no convenient air bleed valve already installed on the airbound section of heating baseboard or radiator.
Of course if your heating system already has air bleeder valves
( see AIR BLEEDER VALVES) installed on high sections of baseboard or radiators (higher hydronic heat delivery baseboards or radiators are the more likelyi ones to become airbound as air naturally migrates upwards to highest piping in the heating system) you should try opening one or more of those first to see if you can bleed out the air.
The following procedure is the more simple of the two we describe for correcting an air-bound hot water (hydronic) heating system, and it avoids the need to use pumps or to install extra service drains that may have been omitted on the heating system.
While this is the easiest and simplest procedure to remove air from an airbound heating system, you might not want to use this method if
In these cases see Procedure #2 at AIR BOUND HEAT SYSTEM REPAIR by PUMP.
Connect a garden hose to the boiler drain and run the end of the hose outside or to a convenient indoor building drain. Open this drain.
Our photo (left) shows a typical boiler drain valve - this one has been leaking, as you can see by the stain on the floor and the mineral deposits on the drain valve.
All boiler drains have threads that accept a standard garden hose.
Contact us if you have other suggestions for improving this procedure. We are pleased to give credit and links to contributing reviewers, authors, or critics.
Continue reading at AIR BOUND HEAT SYSTEM REPAIR by PUMP or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see AIR BLEEDER VALVES - how to locate, inspect, use, or replace automatic and manual air bleed valves on hot water heat to fix cold radiators or baseboards caused by air trapped in the heating system.
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(Feb 18, 2015) Anonymous said:
This site saved me a lot of money time and heartache as a new/first time home owner! I always look things over here before calling a technician. Having this knowledge at hand with pictures and some basic tools and mechanical skills saves time and money. This site coupled with some you tube videos and there are few things you wont be able to accomplish!
(Feb 9, 2012) David Gast said:
I have a hot water heating system in my one story home ( ranch style ). I have purged my system just as you've described doing it here. My problem is a humming noise which develops sometimes in the bedroom which is the greatest distance from the boiler. The baseboard heaters are hot and there is no indication of air in the system. I have an ample crawl space and have inspected the plumbing and see that the installers used a minimal hole to run the copper tubing through but otherwise I can't see or feel why it should make this humming sound. I have even replaced the old expansion tank high above the boiler with a bladder type located lower still above but nearer the boiler. I've replaced my circulation pump which is noisy compared to the old one ( same brand Bell and Gossett series 100 ). Have you heard of this problem before? This hum is very annoying 2:00 in the morning.
(Feb 19, 2012) John said:
I tried to follow your procedures listed above but I am thrown off by the fact that even without a auto fill valve the cold water feed does not refill the system thru the fitting at the amtrol tank? I have a weil-mclain #68 boiler used for heat and hot water. The gurgling noise in the baseboards has slowly gotten noisier until its now a bang/clang on cooling off. No vents on the baseboards and there is no auto fill valve. Three drain valves on boiler 1 on the the ( 2 zone) return line above recirc pump, one at the base of the boiler & one off the cold water feed below the mixing valve. the amtrol tank is mounted high and the vent over it occasionally vents but the noises have not improved. I shut the boiler down and after the temp dropped I ran a hose from the cold water fill below the mixing valve to the drain at the base of the boiler.
I had both zone valves open and cracked the valves while watching the gauge. I then tried opening the valve on the return line but did not notice any air bleed. The pressure stayed around 15+ psi. I am going to recheck for the noises and just want to make sure that the lines are properly filled ( I assume more efficient and minimal to no noise) and to find out why the gauge is usually on 0-5 inspite of being professionally installed (1993) and serviced continually by the same shop. Please let me know if I should run more water out of the return line while feeding the boiler drain until I hear air coming out. Thanks John
(Nov 4, 2012) sarah said:
all my radiators are cold just one gets hot in the bathroom i need help to fix it
John, and also Sarah,
Manual air bleeding at a radiator or other valve or vent only works if the bleed opening is at a high point in the system and is where or uphill and just past where the air blockage is located.
Take a look at the air bleeder valves article and the air bound heat rpair method 2
Both links are in this aricle.
Often it helps to locate the air blockage by turning up the thermostat, and when the boiler is hot, feel piping to see where heat stops.
(Nov 4, 2012) Alex said:
I am not sure - do you drain the system entirely prior to opening the water feeder bypass?
No - none.
Alex, we are not draining water out of the heating system when purging air, we are pushing water in and air out.
(Nov 19, 2012) Todd said:
I have an older system (Boiler gas fired 77) Can't figure out how to drain system to stop the noise. I checked expansion tank and no water came out. The system seems backwards. Water from hot water heater to vertical piping and 3 zone valves off that each with a drain valve and then looks like into cirq pump than boiler. This seems backwards to me. on the output side of boiler has 3 branches off and expansion tank with auto relief valve. I can send photos if needed. Any advise would be great! I'm just trying to make it through the winter then I will replace the system, but I would like to get some sleep in the mean time.
I would like to see some photos of the system and piping arrangement.
But too, our article may have confused you. In general, we don't try to stop air bubbling noise in a hot water heating system by draining water out. Quite the opposite. We want the system piping to have no air in it at all - filled with water.
Draining an expansion tank to get air into that component is correct for non- bladder type tanks, but is a separate topic.
(Nov 28, 2012) OsK said:
Hi, I have a hydronic boiler with lots of zones one of which is for the indirectly heated hot water system. When the flame goes off and all zones are off, the boiler which operates at about 55C or 110F starts heating up and sometimes vents at the overpressure valve. What could be causing this "latent" heat? I suspect either air in the top of the boiler or gunk in the bottom but I have tried to get rid of both, if there was any. If I could add a "run-on" or "cool-off" time to the water pumps (of which there is 3) then the problem would be solved. OsK
Thanks for the helpful comment on radiator & piping temperatures. I agree.
It is also helpful to feel comparable temperatures. For example, I (carefully as surfaces can be quite hot) touch and compare pipe temperatures on the inlet and outlet sides of a zone valve or a (quiet) Taco circulator to see if the valve has opened or the circulator is running.
Indeed for some applications we need to read temperatures more accurately, or we may even need to use thermography or other large area scanning tools (like finding where there is a break in readiant heat tubing in a floor), but just to see if something is open or working, the simple temperature comparison should be enough.
Finally, at least with some themographic equipment such as my Exergen scanner, the temperatures given on the digital readout are NOT accurate unless you are reading at the proper distance and from a flat black surface. Exergen even included a black crayon we use to make a mark on a shiny surface when we're looking for more accurate numbers.
We appreciate your helping-out OsK - together we are smarter than any individual.
Daniel - Editor
(Nov 29, 2012) Craig said:
Exactly how "hot to the touch" should radiators get? Do you define hot to the touch as can't touch them for more then 5, 10 seconds? My radiators get luke warm (not "hot" to the touch)after the boiler has been running.
Craig, your definition of hot to the touch seems about right. Luke warm is ok if it is the last radiator in a long series chained together. If the input side of the radiator is warmer than the output then the radiator is doing its job radiating heat. If the output of the boiler is too hot to touch and the return is cool, then the heat is being transferred to the radiators and hopefully making the rooms warm. If the return on the boiler is also hot while the radiator remains luke warm then there is a problem. I go around and check the radiators with my hand but I also use this temperature tool
- Mastercraft Digital Temperature Reader available from Canadian Temperature
Reply from moderator:
About that odd hot boiler, I thought I answered this question on another page. I agree that it's an unacceptable condition, and regular spilling of a TP valve can be dangerous for some reasons beyond the obvious.
Is it possible that the boiler in question uses a tankless coil that is leaking into the boiler, increasing its pressure or even causing it to cycle on?
If not, check
- using our pipe feeling discussion, is there actually hot water from somewhere draining back into the boiler? (A bad check valve or zone valve?
- the primary control temperature sensor - is it properly placed, using the manufacturer recommended thermal grease, and working?
- the primary control itself
- or of course the problem might be something we haven't though of or can't see via just e-chatting
(Nov 29, 2012) Craig said:
Hey Dan, Thanks for the response. The output is "Warmer" then the input, so I can say with confidence that it is circulating. However, the output right at the boiler, but I can hold it indefinately (its not too hot). I also came across a post regarding the expansion tank (old big steel kind above boiler), if it has water in it to empty it (about 40+ gallons removed) and it would recharge about 11 gals.
I then ran the boiler for 2 hours now and the output is still not very hot to touch. So recap- 1.burners are working fine, 2. the circulating pump seems to be working, 3. the expansion tank has "air cushion," and the thermastat at the burner control is on max. Here it is really bizarre, I can touch the cast iron heat exchanger on the sides no problem, you would think that all the cast iron on the exchanger would be red hot when being cooked for 2 hours???? In the end the room temp maintains 68, I just have a gut feeling it isn't working they way it is suppose to be. BTW thanks for taking the time with managing this site, very helpful!
The output pipe is hotter then the input, I can say for certain the circulating pump is working, but even right at the boiler the output pipe isn't that hot, I can grab it right at the boiler for any amount of time. Crazy is the burners are working and the thermostat is on close to max
. Further, the cast iron heat exchangers aren't that hot on the sides. You would think the anywhere on the exchanger would be red-hot after cooking for hours. Today I emptied the 40+ gals. of water from the expansion tank, when I turned on the water again, the tank filled w/ about 11 gals. (watched water meter).
So pump works, burners work, expansion tank has "air cushion" but the output pipe and radiators are not that "hot" to touch. Thoughts? Thanks for maintaining this site, very helpful!
Craig a waterlogged expansion tank causes relief valve spillage, not indequate radiator heating.
A radiator that is just warm is probably not getting enou heat delivered
Partially air bound or piping uninsulated or temps set too low, or rad valve partly shut
Figure water leaving the boiler is 180 and maybe 140 at a radiator - bllpark,
It would feel quite hot, not ... Warm
(Dec 9, 2012) debbie said:
I have replaced the zone valve, the thermostat and the pressure release valve and 2x purged the pipes getting full stream water coming thru. This 1 room is still not getting any heat and it is on its on zone?
What have I not thought of doing?
(Dec 11, 2012) Tom c said:
Purged the boiler short loop that got hot to the modine convection heater BUT a few min later the supply a the heater would get cool and the aqua stat at the unit shuts d
Purged the boiler short loop that got hot to the modine convection heater BUT a few min later the supply at the heater would get cool and the aqua stat at the unit shuts down waiting for the loop to circulate warm water to the loop as the thermostat calls for heat
There are 2 other loops that circulate with no problem and are longer loops in floors above?
What could be stopping the loop after bleeding it.
Bad check valve, bad TT wire or TT, (TT = thermostat)
Bad circulator relay, air in the system
(Dec 29, 2012) marlo said:
i am purging the baseboards they get hot for 10 minutes then go cold again...whats going on?
(Jan 2, 2013) A. Khan said:
The hot water only runs through finned-tube baseboards located in the dining room and living room, however, it does not run through the baseboards located in the guest room, bedroom and the washroom. I have to zone valves (one for the basement and the other one for the upper level). The pressure gauge on the boiler reads 25psi (seems reasonable). It is an oil fired boiler. I did some purging (by opening the knob and trying to drain some water from the pipes). It did work for a little while, however, it stopped working later. Please comment. I am trying to figure out the system as I go. I am new to this type of system, but keen to learn.
Is it an issue of air in the line or something else?
(Jan 5, 2013) Keith C Lenox Mass. said:
I purge my baseboard heating system but now I do not get any running hot water from any of my taps , The cold water is fine (( when i say no hot water I mean no water at all when i turn on the hot water handles ))Not sure what to do next
(Jan 25, 2014) hearty said:
Last week I had a leak through the light fixture on the first floor which turned out to be caused by a puncture on the heating line running to the second floor (right underneath the baseboard) that piece was replaced.
first we couldn't get heat on the second floor. After bleeding it for a long while, finally heat came out. Now I hear strong bangs on the pipe (there was always this noise but it was mild before). I was told that baseboard needs to be bled when that happens since that is caused by air. However, the noise continues and I have bled it for quite sometime. I went to the basement and have open and close the breathers as well but I didn't hear any air coming from there (although early today it did expel a lot of air) I bled all baseboards and for a bit the noise diminished; however, the bangs increase from time to time. Can you please help how to fix this problem?
It is possible for individual radiators or baseboard sections to remain partially air-bound once air has leaked into the piping system. If your air bleeders are located somewhere lower in the piping system it can be difficult to get that air out. In a severe case no hot water circulates. But it's possible to get *reduced* but not totally-blocked hot water flow from air in the system too.
The options are to use a pony pump to force water around and try to force air out of such locations or to identify the problem sections and install additional air bleeders at high points that will solve the problem.
(Jan 25, 2013) Circulator pump running and red- said:
From what I've read in your site, it would appear that my system may be airbound. I replaced the circulator pump 2 weeks ago and periodically I could get heat to circulate through the system, but the system would stop working shortly after I'd leave the property. I checked again the other day and found the boiler was heating up the water to temperature as called for by the thermostat, and the circulator (taco) pump was running, but neither the supply side nor the return side pipes were hot. The housing of the pump was red hot, but wasn't moving any heat!
I agree that it makes sense to check for an air-bound heating system. Start by feeling pipes leaving the boiler. Are they hot? Where does the hot piping stop?
Re-posting without link:
Sophia Castella said:
A few day's before i have join a service of cooling heater, gain many thinks about that but its post is really fantastic.
(Oct 1, 2014) Jacob Lineberry said:
Thank you for such a useful website - it's saved me so much money and prevented more cold nights ;)
(Oct 6, 2014) Billy said:
I have gas boiler with water based board heating. One room is significantly hoter than any other room in the entire house. All base boards have been bled and the boiler was serviced last year. Do I need to get into the crawl space to shut off one of the base boards water supply? Is that even the answer? Thank you.
Take a look at the heating system distribution piping. Sometimes one baseboard loop is much shorter than others, or closer to the boiler, and can be hotter than wanted IF it is on the same thermostat as other heating pipe loops. If that's the case you can have your plumber install a flow balancing valve to slow or restrict the excessive hot water flow to the too-hot loop.
If the too-hot area is on its own thermostat then that's were to go to adjust the temp.
(Oct 8, 2014) samuel G said:
Hi, i started my furnace and some water started leaking, it stopped and then was oil, so i replace that pump and got a news circulator with a maintenance free design. i purge all the radiators, and the old expansion tank but i still heard some banging in the pipes. all the radiators are hot. am not sure what else to do. am thinking about replacing the old expansion tank. i don't know if that will solve the problem. any help will be very well appreciated.
Samuel there are two articles to review that should help
(Oct 22, 2014) Alan said:
I have three zones: two on te first floor and one on the second. The second floor zone is made up of two loops. One comes up and around the "front" rooms and one for the "back" rooms. The loops leave the boiler as one pipe and then "Y" before traveling vertically to the second floor. They rejoin as one before returning to the boiler. The front loop heats well but the back loop is not heating at all. I think it is air bound. Do I need to drain all three zones to purge the air or can I isolate it and just purge the second floor zone?
Using air bound heat remedy one if the boiler is off how can the valves stay open so the water can forcefully run out. As soon as I shut the boiler off the valves feeding the pipes close. What am I missing in this scenario?
If the zone valves have a manual lever, latch it in the OPEN position. Else you have to power the zone valves and thermostats.
4 Jan 2015 ken said:
so holiday company shows , we run our oil burning boiler more for heat/hot water....then after a few days , the upstairs radiator still carry heat but then we get significant loud air valve release in boiler room filling it with steam , and the floor by the boiler relief is wet .... we turn off system, restart. later and still within 1/2 hr get a another air valve release and a room full of steam . ? what next
Ken what valve is releasing steam: if it's a pressure/temperature relief valve then the system is unsafe and should be shut down for repair.
8 January 2015 Fred said:
I have a split with one zone for the upstairs and one for the basement. No problems in the basement. The upstairs feed off the boiler splits off in two direction, one fro the front of the house and one for the back. The back baseboards are hot, but the front are cold. The return to the boiler is again split, and one of the pipes is cold. What could be the problem. The furnance is oil forced hot water.
I'd look for air bound piping in the cold zone or a zone valve that is not opening properly.
(Feb 18, 2015) AL said:
I have tried closing the gate valve to the boiler and feeding water while trying to remove air to the system ...Lots of air ,,,have tried feed ing water into system while bleeding ,,,cannot get above 72 degrees unless i run t stat at80 allday ,,later its back to72 again
Often air in long horizontal piping runs is difficult to remove by the method you tried. Check out
(Feb 19, 2015) Bill said:
I have a steam/hot water heating system. Originally the system was all steam, than added upstairs extension to house that is running gravity feed water from the boiler. So I'm running steam in one section and water in the other section from the same boiler. When hot water starts to run through the extension, it hammers through most of the pipes, but I do get heat. Question; is it air or cold water sitting in the pipes and how do I fix it?
I'm not sure, Bill, but typically banging pipes in a steam system is traces to a condensate return blockage or a clogged steam trap.
See BANGING HEATING PIPES RADIATORS for more detailed help.
(Mar 3, 2015) Donny said:
I changed out the pressure relief valve today, after all the work was done let the boiler fill back up, everything fired up got to temp and pressure but, found the return side (I believe) with circulator pump on it was ice cold, but supply side (expansion tank side)was super hot. Tried to bleed out air but nothing seems to work. Still in same mess..Any suggestions ?
You may find that just manual bleeding of air doesn't remove the air from long horizontal runs.
Try the procedure at AIR BOUND HEAT SYSTEM REPAIR by PUMP
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