Air-bound heating baseboard or radiator repairs:

Here we explain how to remove unwanted, 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.

How to Diagnose & Fix an Air-Bound Hot Water Heating System

Discussed here: How to diagnose cold heating baseboards or radiators, How to diagnose heating circulator pumps that won't stop running.

A Guide to Air Bleeder Valves on Heating Systems: Heating System Radiator, Baseboard, or Convector Air Bleeder Valve Troubleshooting & Repair Guide, Cold radiators: if your radiators won't get hot : how to check for an airbound radiator and other causes.

Steps to diagnose and fix heating system noises & air in hot water heating system pipes.

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 unwanted 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 HEAT 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

Reply:

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:

1. The heating pipe, baseboard or radiator has become air-bound:
   
   this means that a sufficient volume of air has become trapped in the radiator or hot water distribution piping or baseboard piping so that the circulator is unable to cause hot water to circulate through the heating distribution system.
   
   Keep in mind that most circulator pumps do not have a lot of "lift" or water pushing ability. To be able to move hot water around the heating piping loop the circulator pump depends on the piping being full of water, so that water "falling" on the return side of the heat piping loop reduces the "lift" needed to be provided by the circulator pump.
   
   If this is the problem your heating system is having, the article below explains how to cure the difficulty as well as how to prevent it from happening again.
2. A check or control valve in the heating water piping
   
    system that should be open happens to be closed, such as a stuck heating zone valve or a flo-control valve that has been manually put into the "closed" position.
   
   See ZONE VALVES, HEATING
   
   See CHECK VALVES, HEATING SYSTEM
3. A room heating thermostat may be stuck,
   
   damaged, or set too high, or its wires shorted -
   
   see THERMOSTATS.
   
   On occasion a heating zone control relay could also be stuck or damaged, but we don't encounter that problem often. If the circulator keeps running even when you are not calling for heat, such as in summer (the reader's example above) there could be the problem at the thermostat, zone valve switch, or circulator pump relay switch. Typically we inspect and eliminate each of these in turn.
   
   Watch out: Be careful to turn off electrical power before working on thermostats or other electrical components. In addition to shock hazards, shorting a wire can add to your troubleshooting woes by blowing a hidden fuse (such as on a control board), or damaging a component such as a transformer.
4. The circulator pump itself
   
    could be damaged or defective. Try checking the problems above first. If none of those conditions apply, you may need to replace the circulator pump or pump assembly or motor.
   
   See CIRCULATOR DIAGNOSTICS.
5. There could be some other problem 
   
   we haven't thought of but that your experienced heating service technician may point out.
   
   CONTACT us to add that information here to help others.

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 series 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 unwanted 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.

See AIR BLEEDER VALVES where we explain how to find and use these to bleed air out of various spots in a hot water heating system.

Airbound Heating System Relief Procedure #1 Using Water Feeder & Boiler Drain

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 installed on high sections of baseboard or radiators (higher hydronic heat delivery baseboards or radiators are the more likely 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.

See AIR BLEEDER VALVES for more detail.

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

• The boiler is very hot and it is a cast iron unit that could be cracked by a sudden surge of incoming very cold water
• The heating system has been filled with antifreeze.
• The heating boiler drain (located at or near the bottom of the boiler) is in poor condition and may not be opened and then closed reliably.

In these cases see Procedure #2

at AIR BOUND HEAT SYSTEM REPAIR by PUMP.

Here are the steps in airbound heat remedy #1

1. Turn off the heating boiler,
   
   using the service switch. If necessary,
   
   see ELECTRICAL POWER SWITCH FOR HEAT.
2. Confirm that the heating system appears to be air-bound:
   
   heat is on and boiler temperature is up and the circulator pump is running; by touch the technician confirms that one or more sections of radiator, convector, or heating baseboard remain cold even though all radiator or convector or other circulating system valves are in the open position.

3. 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.

4. Open the water feeder bypass: 
   
   (shown above) Locate and open the bypass or "over-ride" on the automatic water-feeder pressure-reducer on the heating boiler.
   
   On a residential heating boiler the automatic water-feeder/pressure reducing valve that automatically provides makeup water to the heating boiler if pressure drops below 12 psi. (12 psi is for typical U.S. / Canadian residential heating systems normal cold temperature starting pressure. U.K. and European heating systems should be pressurized to between 1 and 1.5 bar - cold.)
   
   Usually this valve has a lever that can be lifted to temporarily bypass the pressure-reducing function and feed water directly to the heating boiler at street water pressure (up to 70 psi).
   
   See WATER FEEDER VALVES, HYDRONIC BOILER for details about how this valve works.
   
   Lift the lever to feed high pressure water into the heating boiler. This should also force high pressure water through the heating distribution pipes, radiators, convectors, or baseboards, forcing air out of those components.
   
   Pressure in the boiler should not exceed 30 psi (otherwise the pressure/temperature relief valve will begin to spill water). Let the water "run" through the heating system, watching the hose output end for evidence that air along with water is spurting out of the hose.
5. Close the water feeder bypass
   
    and quickly move to the next step - just below. This will stop forcing higher-pressure water into the boiler and the heating system piping.
6. Close the boiler drain valve.
   
   This will stop water from leaving the boiler.
7. Set the proper boiler cold water pressure:
   
   The automatic water feeder will put additional water into the boiler until it reaches its starting pressure.
   
   If the boiler pressure is below its normal level 
   
   the automatic water feeder should correct this problem. Watch the boiler pressure fill up to its normal cold pressure setting - typically this is around 12 psi on a two story home.
   
   If the boiler pressure is too high and the boiler is cold, 
   
   use the boiler drain to drop the boiler pressure to the proper starting level.
   
   See WATER FEEDER VALVES, HYDRONIC BOILER for a description of the typical pressures needed in residential hot water heating systems depending on the height of the highest radiator or baseboard above the heating boiler.
8. Turn on the heating boiler and assure that the thermostat is calling for heat.
   
   When the system has reached normal operating temperature and pressure, check the radiators, convectors, or baseboard sections that were previously cold - they should now be warm.
   
   If the previously cold radiator (etc) still remains cold, either you have not removed enough air from the system or there is another problem causing loss of heat. In that case
   
   see HEATING LOSS DIAGNOSIS-BOILERS.
9. Check the boiler drain valve
   
    to be sure it's not leaking. In an emergency we screw a garden hose cap on the end of a leaky heating boiler drain.
10. Monitor heating system operation:
    
    we never leave a property where we have worked on the heating system without first checking for leaks, inspecting for obvious safety hazards (such as a bad relief valve, blocked flue, improper oil or gas burner operation), and confirming that the heating system runs through it's on-off cycle normally.

How Do we Know That the Air Bleed Valve Operation Has Been Successful?

• If you open a manual air bleeder valve on a hot water heating system and air hisses out,
  
  there was air that needed removal. If only water comes out, that device was not the one that is air bound.
• If the heating boiler is already running and hot,
  
  quite quickly, in a few minutes the baseboard radiator or convector that was air bound will get hot to the touch. Feel first at the pipes that enter the radiator, convector or heating baseboard since that's where hot water will begin entering the previously air-bound device.

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.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Is it OK to add cold water to a hot water heating system?

What are you talking about above adding cold water to a hot system am I reading that wrong? - On 2022-01-08 by Bret

Reply by InspectApedia Com Moderator (mod) - Watch out: for risk of thermal shock damage when putting cold water into a boiler

@Bret,

Watch out: You are correct in implying that thermal shock caused by sudden addition of large volume of cold water into a very hot cast iron boiler could cause a ruinous crack in cast iron.

Adding water or using a pony
pump to force out air from an air bound system should start slowly so as to avoid that risk.

It's a widely used and successful step in the hands of trained technicians.

Water sloshing sound after new boiler installed - recurrent air problem

I had a new boiler put in. Now the water sloshes through the pipes. They have come and drained the air out twice, but it keeps coming back. What would cause this and how do you fix it? - On 2021-01-29 by Chris

Reply by danjoefriedman (mod) - fix sound of water sloshing in heating pipes

Chris:

Either the air removal process being used has been insufficient or there is a leak that's allowing more air into the system piping (and possibly water out).

I'd try the procedure on this page and I'd inspect every inch of the system for leaks.

One baseboard won't heat up

I have a problem with 1 of my baseboards not heating up with a hot water system. I turn on the thermostat and let it go for 20 minutes. i check all the other baseboards upstairs and they are all heating up.

I go to the problem baseboard and open the air bleeder valve and only water comes out in a steady stream. I hear no air hissing. What do i do?

i should also add that the intake on the baseboard feels warm but the fins dont heat up. - On 2020-10-11 by Jimarac

Reply by danjoefriedman (mod) - some baseboards won't get hot

I'd be looking for an air blockage that's ahead of the section of baseboard where you report it not-heating. The article on this page describes more-aggressive forcing of air out of a hydronic heating system that we try when individual air bleeders along the baseboards are not solving the problem.

Of course you've already checked that there's no zone valve shut or circulator not running, right? If not some of the diagnostics suggested

at NO HEAT BOILER may help you out

Your Procedure to bleed air out of my hot water heating pipes worked

I got to the point where no water and no air was coming out of my bleeders. "Airbound Heating System Relief Procedure #1 Using Water Feeder & Boiler Drain" worked perfectly.

I was worried about all the pressure going through my old system so I just cracked the feeder valve slightly. As soon as I did I could finally hear water running through the pipes. in seconds it went throughout the system and out the drain.

Outstanding... thank you On 2019-12-20 by Vinny

I failed to mention the outside wood boiler, (pacific western) isn't closed since all I have to do is put a hose in the open pipe on top. Now the leak it has in tank, would that cause issues? Shop has no problems I'm guessing because its on the uphill side. Thanks again. - On 2020-01-29

Reply by (mod) -Your airbound heat solution worked perfectly

Anon / Vinny

Thank you for an interesting question and discussion. I would very much like to help but frankly I don't understand enough about your system and its installation. It looks to me as if you understand the basic concept correctly which is do look for places that are could be grown into your hot water piping system.

If the hose Arrangement that you describe would allow are to be drawn in, that would certainly be a problem source.

Getting air in wood-boiler hot water heating system

I have installed a wood boiler (unpresserized) system, which is also heating a shop, to a closed (pressureized) hydronic floor heat system for the house/earth home.

The system in house works good for a week to 10 days then i have to pressurize it do to, what im guessing, air in the system. What do I need to fix this issue? Thank you. - On 2019-12-09 by Marvin

Reply by (mod) -

Marvin I can but make a wild guess as I know so little about the situation;

1. have you installed an air purge on the closed system - or perhaps more than one depending on the piping layout? Automatic air vents work well for minor air in hydronic heating water.

2. if the system is recurrently air-bound we need to find and fix the leak - air in and perhaps water out.

In the ARTICLE INDEX look at the articles on AIRBOUND HEATING SYSTEMS

Fix gurgling in pipe/radiator system where a Spirovent is installed

There are just circulator pumps and no zone valves. There is some gurgling in the pipe/radiator system but goes away when individual radiators or baseboards are bled.

The 2 times that the circulator was air bound the problem was remedied by purging the system right at the circulator. This seemed to get water into the circulator and hot water would then pump through the system.

I have a 2 year old boiler using Taco circulators for 2 heat zones and hot water storage tank.

Each of the last 2 years when the thermostat called for heat for the first time after not having run all summer (except for personal hot water), the first floor circulator would run but not pump water.

I bled each (cast iron baseboard and radiator) on the first floor, which immediately spouted water, not any air.

I then went to the boiler, closing off the first floor return, connecting a drain hose and opening the drain petcock while opening the cold water quick fill valve.

Water flowed right away, seemingly without air. There is a Spirovent brass microbubble resorber on the supply line right out of the boiler and just before the first floor circulator. There is no noticeable leak or corrosion of any of these lines. Any thoughts? - On 2019-10-02 by Don

Reply by (mod) -

Because the problem is recurrent I'd

1. be sure that the air purger at the boiler is working - or replace it; also be sure it's properly located (high on the outlet side above the boiler)

2. install automatic or manual air vents higher in the building- at high end of high runs or rads or baseboards

3. take a close look at all accessible boiler connections and hot water heat piping for corrosion or other signs of leaks out - that might also be air-leaks-in when the system cools.

...

Continue reading at AIR BOUND HEAT SYSTEM REPAIR by PUMP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE FAQs - questions & answers posted originally at this page.

Or see these

Recommended Articles

• AIR-BOUND HEATING SYSTEMS - home
• AIR BLEEDER VALVES
• AIR BLEEDER VALVE FUNCTIONS
• AIR BLEED VALVE INSTALLATION
• AIR BLEED VALVE LEAK REPAIR
• AIR BLEED VALVE SOURCES
• AIR ELIMINATOR / FLOAT VENT REPLACEMENT
• AIRBOUND RADIANT HEAT
• AIRBOUND HEAT SYSTEM REPAIR by PUMP
• AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
• AIR SCOOPS PURGERS SEPARATORS
• BANGING HEATING PIPES RADIATORS
• BANGING HEATING ZONE VALVES
• DISSOLVED OXYGEN DAMAGE CONTROL - use of bulk air eliminators on hydronic heating systems helps avoid damage from dissolved oxygen
• NO HEAT BOILER - diagnose causes of loss of heat
• RADIATOR PLUG REMOVAL
• RADIATOR VALVES & HEAT CONTROLS

Suggested citation for this web page

AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING RADIATORS

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