Guide to Fixing an Air-Bound Hot Water Heating System - Procedure#1, Using Built-In Controls & Valves InspectAPedia® -
Service Procedures to force air out of an air-bound hot water heating system
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
How to diagnose and fix heating system noises & air in hot water heating system pipes
Our site offers impartial, unbiased advice without conflicts of interest.
We will block advertisements which we discover or readers inform us are associated with bad business practices,
false-advertising, or junk science. Our contact info is at
InspectAPedia.com/appointment.htm.
Here we discuss 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 radiators of your building are not getting hot, the discussion here can help diagnose and cure that problem.
Here we explain how to locate, inspect, 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 airbound pipes in a hot water heating system. This article is divided into these main sections:
Our discussion of radiators or baseboards that do not get hot when they should includes these key sections:
Air Bleeder Valves - a Guide to Air Bleeder Valves for Hot Water Heating Systems: Radiators, Baseboards, Convectors - how to find and use manual and automatic air bleeders to fix noisy gurgling heating pipes or an airbound heating system. Air purges for steam heating systems are discussed separately at Steam Vents.
Airbound Heating System Relief Procedure #2 Using a Pony Pump - how to use a portable pump, short sections of garden hose, and heating system valves to force air out an air-bound heating system whose radiators, convectors, or baseboards are not warming up.
Water Feeder Valves, Hydronic - a defective automatic water feeder valve on a hot water heating boiler can result in too little starting water pressure in the system - radiators on upper floors may fail to receive heat. On a steam heating boiler a defective automatic water feed valve can cause the heating system to shut down completely or can lead to boiler damage or even unsafe conditions.
At BOILER PRESSURE & TEMPERATURE SETTINGS we discuss the pressures needed for hydronic or hot water heating systems - a taller building needs higher starting (cold) pressure in the heating boiler. At Water Feeder Valves, Hydronic we discuss problems with water feeder valves that also control water pressure in the boiler and we explain how to adjust the water feeder valve and thus boiler water pressure. If your heating system uses a steam boiler, see Water Feeder Valves, Steam.
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 website 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 you don't know what kind of heat your building uses, see our introduction at BOILERS, HEATING. If your heating system is not working properly, see NO HEAT - BOILER / FURNACE DIAGNOSIS.This website 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.
Service Procedures 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. See Air Bleeder Valves and then How to Open Manual Air Bleeder Valves.
Airbound Heating System Relief Procedure #1 Using Water Feeder & Boiler Drain
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.
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.
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.
Open the water feeder bypass: 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.
Close the water feeder bypass and quickly move to step 6 just below. This will stop forcing higher-pressure water into the boiler and the heating system piping.
Close the boiler drain valve. This will stop water from leaving the boiler.
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.
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.
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.
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 minute or three, the 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.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
Steam Vents provides details about air vents or steam vents on steam heating systems and diagnoses hissing sounds and failure of a steam radiator to get hot.
Thermostats & Heat Controls for furnaces & boilers, oil & gas fired, heat pumps or electric furnaces or boilers
Water Feed Valves: A guide to water-feeding/pressure-reducing valves on hot water and steam heating systems
Zone Valves: A guide to zone valves for heating zone control on hot water heating systems
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
More Information on Building Diagnostic Inspections and Repairs
...
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
Mobile View 
InspectAPedia ® Home & Site Map 
Open the water feeder bypass: Locate and open the bypass or "over-ride" on the automatic water-feeder pressure-reducer on the heating boiler. 
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest. 
