Air bound Hot Water Heating System Diagnosis & Repair

How to fix cold baseboards, pipes, or radiators due to air blockage

What to check first if a hot water heating radiator or baseboard is not getting hot

Check hot water baseboards, radiators, or heating convectors:

if some of these heating devices are hot and others cold, are they all on the same heating zone?

Feel the hot water piping leaving the heating boiler - it should be hot when the boiler is running and the thermostat is calling for heat.

If the building has multiple heating zones each zone will be controlled by its own thermostat and each heating zone will either have its own hot water circulator pump (controlled by a thermostat and pump relay switch), or each hot water heating zone will have its own thermostat and a zone valve that opens to let a common circulator pump send hot water through that individual heating zone

Are all of the thermostats turned up high enough to call for heat in each heating zone?

If some heating baseboards or radiators are hot and others cold 

and we're sure that they're on the same heating zone, then the system is probably air-blocked.

Watch out: it is not obvious to people not expert in hot water heating systems, but the circulator pump on a typical hot water (hydronic) heating system does not have enough oomph to push a bolus of trapped air around through the heating system pipes.

If more than small bubbles of air remain trapped inside the heating piping the circulator may spin without actually pushing hot water through the system. By purging the trapped air we get the hot water circulating again.

See details at COLD HEATING RADIATOR REPAIR (hot water / hydronic heat)  

5 Approaches to Removing Hydronic Air / Fixing an Air-Bound Hydronic Heating System

In sister articles we discuss these approaches to removing air that is preventing proper water circulation in a hydronic (hot water) heating system.

You are likely to find at least two of these automatic and manual air removing devices on both residential and commercial hot water heating systems: air bleeder valves, both automatic and manual, and air scoops/separators.

1. AIR BLEEDER VALVES
   
   are installed at the boiler and at other strategic locations automatic or manual air bleeders remove air from the system at high points.
2. AIR SCOOPS SEPARATORS PURGERS
   
   (the read "Deaerator" at the boiler's outlet or hot water out pipe in the drawing, are specialty valves that in essence are a more-sophisticated "air bleeder valve" - the first de-aeration approach in this list.
   
   An example of air separator products is the
   
   Nexus Valve Flamco Flamcovent Smart air separator. Retrieved 2017/12/14, original source: http://www.nexusvalve.com/products/categories/?cid=10065&tid=10027
   Excerpt from the company's web page:
   
   The Flamcovent Smart air separator removes even the smallest microbubbles from the system water. It is virtually maintenance-free with a negligibly low flow resistance.
   
   The Flamcovent Smart can be incorporated in a variety of heating and cooling systems and in every desired direction.
   
   Others include Spirovent deaerators and Taco air scoops - illustrated later on this page.
3. AIR BOUND HEAT SYSTEM REPAIR by PUMP - using a pony pump to force air out of an air-bound heating system
4. AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE - using a pressure over-ride on the boiler water feeder to try to force air out of an airbound heating system
5. PRESSURE-STEP DEAERATORS [PDF] - Nexus Valve Flamco Pressure Step Deaerator, Aalberts Industries, 9982 E. 121st St., Fishers IN 46037, USA Tel: 888-900-0947, Website: www.nexusvalve.com Retrieved 2017/12/14, original source: http://www.nexusvalve.com/uploads/downloads/Flamco%20PSD%20FINAL.pdf
   
   Excerpts:
   
   Pressure-Step Deaerators or PSDs are a more-recent innovation used to remove entrained air in hot (or chilled) water hydronic systems.
   
   "Entrained" air can be taken to mean air that is dissolved in the hydronic system's water. As water is warmed that entrained air changes to gas bubbles that in quantity can result in an air-bound piping system.
   
   A pressure-step deaerator uses vacuum to "deaerate" or remove air entrained in the hydronic system's water.
   
   The PSD from FLAMCO uses a combination of duplexed pumps, isolation valves, and a vacuum deaerator cylinder along with additional controls and valves to remove air dissolved in the system water supply.

Technical note: building plumbing systems may include other water system air removal devices not associated with heating and cooling, such

as AIR ELIMINATORS for POTABLE WATER SUPPLIES

Diagnose Causes of Persistent Air in Heating System Piping: noises, cold baseboards/radiators

Diagnose & fix recurrent noise of air in hot water (hydronic) heating piping, baseboards, radiators:

If your service technician bled all of the air from the heating system piping but the problem returns, then most-likely the problem is one of these three causes:

1. The service technician did not actually get all of the air out of all sections of heating system piping, baseboards, radiator, boiler.
   
   For example, if air bleeding is incomplete or not done properly, even though the plumber says the job is "done" it might not be.
   
   For example, unless the heating technician or plumber uses a pump to force water through the system to flush out all air, some air may be left in piping, especially at longer horizontal runs.
   
   See details at AIR BOUND HEAT SYSTEM REPAIR by PUMP 
   
   
2. Your heating system is missing automatic air bleeder valves or the ones installed are not working.
   
   If your service technician successfully bled all of the air from the heating system piping but the problem returns, then most-likely the problem is that either your system is missing automatic air bleeder valves or the ones installed are not working.
   
   After having the service tech confirm that the primary air removal device at the boiler,
   
   see AIR SCOOPS SEPARATORS PURGERS 
   
   and check that all other automatic air bleeder devices installed on the heating system and its piping are working:
   
   See AIR BLEEDER VALVES 
3. Check for leaks in the heating system boiler, controls, or piping.
   
   In addition to making sure that the two key automatic air removal devices that we mentioned above,
   
   look for signs of a leak anywhere in the system piping or at the boiler or controls.
   
   A water leak out is also a possible air leak in when the boiler is in an off cycle and is cooling down.
4. Other air removal and heating system air noise remedies
   
   Be sure that you have reviewed all 9 of the air-bound heating system cures just below on this page.
   
   

Cures for Air in Heating Systems

Our discussion of radiators or baseboards that do not get hot when they should includes the articles listed below explaining how to get rid of air in hot water or hydronic heating systems in order to prevent or cure air-bound heating systems (sections of baseboard or radiators that don't get hot).

1. AIR BLEEDER VALVES - Guide to manual and automatic air bleeder valves & vents for hot water type heating systems:
   
   how to find and use manual and automatic air bleeders to fix an air-boundheating system causing cold radiators convectors, or baseboards or noisy bubbling, gurgling heating pipes.
   
   The air bleeder valve article series also explains how to troubleshoot, fix, install, or repair manual air purging or air bleeding valves on heating equipment. Some of these valves also work on cold water used in chilling and cooling equipment.
   
   at AIR BLEED VALVE INSTALLATION.
2. AIR SCOOPS SEPARATORS PURGERS: guide to automatic air purging devices:
   
   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.
   
   A quick visual inspection can tell us if there is obvious leakage, corrosion, or clogging of some automatic air separator devices, and fdor some automatic air purge valves, a simple step of opening a valve cap may be all that's needed to restore the valve to operation - or perhaps we close the cap to stop dripping there.
   
   Air vents necessary for steam radiators to get hot for steam heating systems are discussed separately
   
   at STEAM VENTS.
3. AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE - describes how to use built-in controls and valves to force air out an air-bound heating system
   
   whose radiators, convectors, or baseboards are not warming up. We try this approach if trapped air in the heating system piping or baseboards is not being successfully vented by the manual or automatic vents already installed.
4. AIR BOUND RADIANT HEAT - a no heat problem in one zone of radiant heating may show up as a "vacuum"
   
   or as "heat is running backwards" or may be mistaken for a thermostat or control problem, depending on the controls installed and where you look
5. AIR BOUND HEAT SYSTEM REPAIR by PUMP - (photo above) 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.
   
   Photo above: a pony pump and hoses being prepared to force water through an air-bound heating system to push un-wanted air out of piping when air bleeders themselves are not doing the trick.
6. STEAM VENTS - are installed around the middle of one end of steam heat radiators to vent air as steam rises into the radiator.
   
   These vents are automatic. If the steam radiator does not heat and its feed valve is open try replacing the steam vent.
7. 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.
   
   Gurgling noises in the heating system pipes or low heating boiler water pressure could be due to a clogged or damaged pressure-reducer water feed valve. Here is an example:
   
   After I was unable to figure why the furnace had a low water level that led to gurgling in the radiators, I decided to change the auto-fill valve above the expansion tank. I'd already changed the tank the week before but decided to cheap out and reuse the old valve.
   
   When I disconnected and upended the tank/valve it spilled a bunch of black sulfur laden water out. The sulfur flakes may have clogged the screen or valve for as much as several years. - M.F. 12/24/2014
   
   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. In this article we discuss problems with water feeder valves that also control water pres sure in the boiler and we explain how to adjust the water feeder valve and thus boiler water pressure.
   
   Here are two air-removal remedies that can work
   
   AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE - and if this doesn't work then
   
   WATER FEEDER VALVE, STEAM is the article you want if your heating system is by steam rather than hot water.
8. 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.
9. At OIL HEAT NOISE DIAGNOSIS we discuss the diagnosis and repair of other heating system noises on both oil and gas fired heating equipment.

Technical Resources on Venting Air From Heating Systems

• Grundfos, VENTING AIR from HEATING SYSTEMS [PDF] Grundfos, Poul Due Jensens Vej 7 DK-8850 Bjerringbro, Denmark Tel.: +45 87501400 retrieved 2020/04/15, original source: https://www.grundfos.com/service-support/encyclopedia-search/air-vent.html
  
  Excerpt:
  
  Air can still be present in a system filled with water even after the system has been vented using air vent screws and air vents. This is because the water contains a certain volume of air, depending on ambient pressure and temperature at the time the system is filled.
  
  The air is released when the water is heated in the boiler or heat exchanger and in low pressure areas in the system, such as at the highest point in the system or on the suction side of a pump.
  
  The released air consists of oxygen and nitrogen. The oxygen binds to any iron materials in the system. The microbubbles of the remaining nitrogen gasses must be removed by another means.
  
  GRUNDFOS Kansas City 17100 West 118th Terrace Olathe, Kansas 66061 USA Phone: (913) 227-3400 www.grundfos.us
  
  GRUNDFOS Canada 2941 Brighton Road Oakville, Ontario L6H 6C9 Canada Phone: +1-905 829 9533 www.grundfos.ca
  
  GRUNDFOS México Boulevard TLC No. 15 Parque Industrial Stiva Aeropuerto C.P. 66600 Apodaca, N.L. México Phone: 011-52-81-8144 4000 Fax: 011-52-81-8144 4010 www.grundfos.mx
  
  Excerpt:
  
  The following are commonly used components and methods to remove air:
  
  Air vent screws mounted on radiators and convectors, etc
  
  Air pots which are placed at high points in the system, often where the pipe goes from horizontal to a vertical drop
  
  Automatic air vents placed in the same way as air pots
  
  Micro-bubble air vents located in front of main pumps where the pressure is lowest
  
  Degassing using a pressure reduction technique where a portion of the system water is diverted to a pressureless diaphragm tank in the system’s pressure-holding and expansion system
  
  Air that is not removed from the system will collect at high points in the heating system and create air pockets. Worst case is that circulation in the heating system comes to a standstill, and the system loses its ability to heat the building.

Above: an AA/R002 & AA/R007 SpiroVent deaerator used on high temperature hot water / heating systems.

• SproVent Deaerators, Churchill-laan 52 5705 BK Helmond Netherlands Tel. +31 (0)492 578 989 Web: https://www.spirotech.com/products/spirovent/ - distributed world-wide.
  

Above, a Taco Air Scoop widely used on hydronic heating systems. Air in hot water leaving the boiler is "scooped" into the top of this device where it is vented using a float-type automatic air vent. A bottom tapping permits installing this device along with a small pressure tank.

More about these devices is

at AIR SCOOPS SEPARATORS PURGERS

• Taco Comfort Solutions, 160 Cranston Street Cranston, RI 02920 USA, Tel: 401-942-8000 - Taco Air Scoops and air vent deaerators - in our experience probably the most-traditional and widely-found air remover on hot water heating systems.
  
  Taco catalog excerpt:
  The Taco Air Scoop® is specifically designed to provide a noiseless, air-free hydronic heating, cooling or combination system, by efficiently separating out the air from the water in any of these systems.
  
  Operation
  
  Air being lighter than water, it travels along the upper portion of a horizontal pipe in low velocity hydronic systems. As the air and water enter the Air Scoop their velocity decreases, permitting the air bubbles to be scooped up by the baffle and directed to the top of the chamber.
  
  The air reaching the top of the air scoop is either immediately vented through a Hy-Vent® or it moves into a conventional plain steel expansion tank (models 433, 434, 435, 436, and 437), if used.
  
  Should the air completely fill the plain steel tank and back down into the Air Scoop, the excess will be removed by the Hy-Vent without disturbing the operation of the system.