Fix an Air-Bound Hot Water Heating System

Why are Some of my Heating Zones or Radiators Not Getting Hot?

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.

If your heating system is not working properly,

see NO HEAT - BOILER or NO HEAT - FURNACE.

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.

How do I Stop the Sound of Water Running and Gurgling thru the Heating Pipes?

I just purchsed this home. Its heat is hydroponic with a cast iron boiler (oil fired). It seems to heat OK, but always we always hear water running and gurgling thru the pipes.

This is unsettling at night for my little girl.

Is this normal to hear these noises? The house was made in 1960.

HVAC guy wants 90$ an hour to come and bleed it. On 2018-01-24 by larry

by (mod) - try first the air bleeder valves, then read our airbound heat advice

Larry

If you hear water running in the heating pipes there is air in the system that needs to be purged. The risk is loss of heat from an air-bound system.

When you pay your guy $90. to bleed the air you might want to also ask that the automatic air bleeders be left in working condition or that if they are not working they be replaced.

Details of how this repair is done are

at AIRBOUND HEAT - cold baseboards, radiators, noisy pipes

but in your case while there is air in the system there's not so much that it is totally blocking heat flow, it just makes those gurgling noises in the heating pipes.

Often the repair is as trivial and inexpensive as looseing the cap on an air bleeder valve or replacing an air bleed valve that is not working.

So before calling your HVAC guy,

read AIR BLEED VALVE LEAK REPAIR and take a look for these devices at your boiler and along the heating pipes, usually near the ends of heating baseboard runs. See if any of them are leaking and see if their little valve caps are properly loosened.

Aso see DIAGNOSE OIL HEAT NOISES for diagnosis and repair of other heating system noises on both oil and gas fired heating equipment.

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.