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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
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
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.
Question: Why does my heating circulator keep on running?
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:
Service Procedures: How to Fix an Air-Bound Hot Water Heating System
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
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.
Here are the steps in airbound heat remedy #1
How Do we Know That the Air Bleed Valve Operation Has Been Successful?
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 the More Reading links shown below.
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Frequently Asked Questions (FAQs)
(Feb 9, 2012) David Gast said:
Question: help fixing cold radiators
(Feb 19, 2012) John said:
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:
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
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.
Question: how much draining of the boiler is needed before opening the water feed bypass
(Nov 4, 2012) Alex said:
No - none.
Alex, we are not draining water out of the heating system when purging air, we are pushing water in and air out.
Question: Can't figure out how to drain system to stop the boiler air noise
(Nov 19, 2012) Todd said:
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:
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:
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
- 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,
(Dec 9, 2012) debbie said:
What have I not thought of doing?
Question: Modine convection heater operating problem diagnosis
(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 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
Bad check valve, bad TT wire or TT, (TT = thermostat)
Bad circulator relay, air in the system
Question: leaks due to puncture in heating line, trouble getting heat, noise complaints
(Dec 29, 2012) marlo said:
(Jan 2, 2013) A. Khan said:
(Jan 5, 2013) Keith C Lenox Mass. said:
(Jan 25, 2014) hearty said:
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:
Question: one roof is much hotter than any others
(Oct 6, 2014) Billy said:
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.
Question: water leaking from "furnace" then oil leaks at steam boiler
(Oct 8, 2014) samuel G said:
Samuel there are two articles to review that should help
Question: isolate and purge just problem piping loop in air bound system
(Oct 22, 2014) Alan said:
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.
Question: loud air release at boiler and steam in the boiler room
4 Jan 2015 ken said:
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'd look for air bound piping in the cold zone or a zone valve that is not opening properly.
Questions & answers or comments about fixing an air-bound hot water heating system
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