Air-bound heating baseboard or radiator repair FAQs:

Frequently-asked questions about 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 valveOn a heating boiler.

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.

FAQs help Fix a Cold, Air-Bound Hot Water Heating Baseboard or Radiator

Discussed in this second set of FAQs: How to diagnose and fix cold heating baseboards or radiators, and how to diagnose and fix heating circulator pumps that won't stop running.

These questions and answers about air bleeders and air removal valves used on hot water (hydronic) heating systems were posted originally at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE - be sure to see the diagnosis and repair steps given in that article.

Also see AIR BLEEDER VALVES - found at various hot water heating system locations

Also see AIR BOUND HEAT SYSTEM REPAIR by PUMP - a repair process used if you can't bleed air out of an airbound hot water heating system.

On 2018-01-01 by (mod) - cold downstairs, warm upstairs

Brenda

Let's start by finding the brand and model of furnace you have in your attic, then find the installation and operation manual for it. There we will find a specific guide to error lights and codes.

For other readers: while many people use the word "furnace" for any sort of heating system, strictly speaking "furnaces" usually refer to forced hot air systems while "boilers" usually refers to hot water or steam heating systems.

Air bound systems and the need to get air out of a heating piping zone to fix cold baseboards or radiators is a problem for boilers and hot water heat, not hot air heat.

On 2018-01-01 by Brenda

I have 2 zones for heating. I have two thermostats - one upstairs and one down. The upstairs is nice and warm. Downstairs is freezing and not actually heating when heat is being called for. I have Honeywell TH421D thermostats.

The furnace is in the attic. It has some sort of sensor thing on it and it shows zone one with a blinking amber light and zone two is greensand the heat shows green as well. Is there something i can do myself to get zone 2 to work?

On 2017-12-25 by (mod) -

Air that is entrained in the water can be forced out as a gas when the water is heated. Weeks in a system could also blow air into some heating systems.

On 2017-12-24 by Mij

What are the causes for an airbound zone? Where did the original water go ?

On 2017-12-16 7 by (mod) -

Dale

Air removal from hot water piping is a heat distribution problem: air trapped in heating lines blocks water flow; circulators don't have much lift capacity and depend on system water pressure. So when an area is cold I suspect you need to remove air from piping or radiators involved.

That's done by any of several methods discussed in this article series.

The parts of your question referring to "a back" and "a modine" are not parts I understand.

On 2017-12-15 by Anonymous

That's back

On 2017-12-15 by Dale

I've got a back that is only giving me heat to the shower and radiant heat in the floor ,but not up stairs or in my barn ,which is a modine

On 2017-12-08 by (mod) -

Tony,

one of the things to check is discussed in the article AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE. The others can be found by using the search box to find our article titled cold radiators.

Good luck on your test

On 2017-12-07 15:00:12.460250 by Tony

If you lack of heat in an individual radiator or convector what are 4 things to check

On 2017-11-23 01:35:14.992101 by (mod) -

Dave,

I think so, but you'll probablt have to feed in at the boiler drain and take the loop back out at the higher valve that you described. The problem was trying to force out air pumping backwards through the system is that you may run into check valves that will not let the water circulate.
And yes you could have a circulator pump with a bad impeller.

Hopefully you won't freeze everyone out during Thanksgiving

On 2017-11-23 01:04:28.179997 by Dorky Dave

Thanks for responding MOD. The only ball valve with a tee off for a garden hose connection is on the return lines heading back down to the boiler and also at the bottom of the boiler. It may sound impractical, but can I do a 'reverse' power flush with my type of set up?

The only other possible concussion I can come up with is that circulator pump for this zone is not producing enough pressure since the failing kick-space heater is last on the loop zone before heading back down to the return lines.

Have a great Thanksgiving.

On 2017-11-18 02:03:03.590988 by (mod) -

Dave,

Indeed it can be difficult to force air out of all sections of an air-bound heating system. Sometimes I see a nearly horizontal pipe run that holds onto air; that's where the bleeder valves alone won't work. Instead the technician forces water through the whole system with a more powerful pony pump to push air around and out even when it has to push the air "down".

That approach is in the CONTINUE READING recommended link https://inspectapedia.com/heat/Air_Removal_Pump.php

On 2017-11-18 01:25:30.932188 by Dorky Dave

Very intuitive article.

However, even after applying this technique, the pipes leading into/out one of my kick-space heaters are sill cold despite the fact that the kick-space heater in the the other room as well as the rest of the loop that makes up the entire zone on the floor works fine.

Any suggestions?

On 2017-10-30 16:57:48.560288 by Joe pappa

Banging of pipes recently. Sometime the radiators furtest away from furnace dont heat up enough

On 2017-10-12 02:03:41.404378 by (mod) -

Francis,

Thank you so much for the nice feedback.

We work hard to provide useful information, so I'm especially grateful when a reader finds it so.

Questions, critique, or content suggestions are also always very welcome here.

On 2017-10-12 01:45:35.405694 by Francis A King

Many thanks for this clear and concise description of the issues surrounding possible air bound heating zones. I was able to figure out the one thing that had been preventing success in my bleeding efforts (not bypassing the pressure control going into the furnace water input). Once I bypassed it the air started coming out. Thanks!!!

On 2017-03-04 18:43:04.065851 by (mod) -

Anthony

When you are bleeding a radiator on the top floor of a building it's particularly important that the heating system be up to full temperature and pressure - otherwise there may not be enough pressure in the system to force hot water up to that rad.

First be sure that the radiator valve is open (counter-clockwise) but if it's stuck don't force it as you could break it.

Then turn the thermostat up and watch your boiler to see that the boiler runs, the circulator(s) run, and let it run until the boiler turns itself off.

Then try bleeding the radiator again.

Finally, check the boiler pressure when the system is cold. If pressure is below 12 psi the system may not be properly adjusted.

On 2017-03-04 03:21:52.662101 by Anthony

I have one radiator on the top floor that is cold. I tried to bleed it but nothing comes out.

On 2017-02-28 14:55:46.527083 by Will

I will, thanks.

On 2017-02-20 22:06:38.949371 by (mod) -

You can often confirm that by watching the system pressure when the heating system is off and has cooled down.

CHeck in detail for other air bleeders that could be seeping

On 2017-02-20 17:02:17.657907 by Anonymous

No, oil fired hot water baseboards. The expansion tank is small, hot in the top and cool in the bottom and only two years old. There are no attic tanks or additional expansion tanks that I know of. As far as I know all of the first floor pipes run above the basement ceiling (under the hardwood first floor) so any leaks would be visible in the basement ceiling tiles. The second floor pipes presumably run in the first floor ceilings under the second floor hardwood floors.
There was some evidence of a small leak in the basement ceiling a few years ago but I'm not even sure that was a heating loop, I think it was domestic water.

Yeah....I'm confused. It has to be a hidden leak.

On 2017-02-16 18:52:42.146923 by (mod) -

Aside from the possibility of a hidden leak, I'm stymied too. This is not a steam heating system, right? Also: is there a large or are there multiple expansion tanks on the system? Could they have been increasingly waterlogged? Have you checked that
- there are no leaky relief valves
- there is no antique attic overflow that drains into a vent, drain, or outside the building

On 2017-02-16 18:10:51.739917 by Will

Yeah, I can't figure that part out. There's no evidence of leaking water anywhere at all.

On 2017-02-15 21:31:19.827265 by (mod) -

Will,

That's progress at keeping the system running, but if the water feeder keeps feeding water to a hyrdonic heat (forced hot water, not steam) boiler then something's wrong and there's a leak to be found and fixed. Ask ourselves: where is that leaking water going. Probably it's up to no good.

On 2017-02-12 21:40:36.853358 by Will

I've finally found a cure, albeit a band aid. I swapped the auto-fill pressure reducing Watts SB1156F for a new one and left it at the preset pressure, purged the air and it came back again within the same couple of days as before. So, having given up hope of anything else working I decided that since the boiler gauge pressure was consistently going down before the air was audible there must be a water pressure issue of some kind. That said, I increased the auto-fill water pressure on the Watts until I could hear water entering the system. As soon as I heard the auto-fill topping up the system I stopped increasing the pressure. That was a week ago and still no air. The operating pressure is constant at around 27psi. Not ideal.....but no air.

On 2017-02-11 17:59:28.902555 by (mod) -

MB: the steam heat radiators won't be "air bound" - the article AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE discusses air blockage of hot water in hydronic or hot water heating systems.

But your added-back radiators may not be draining steam condensate properly, perhaps because they're sloped the wrong way or because rust or crud is blocking condensate from draining back out of the system.

Search InspectApedia.com for BANGING STEAM PIPE NOISE to see details of diagnosing and fixing that problem.

On 2017-02-11 17:08:21.515515 by MB

We have a one pipe steam heat system with an oil furnace. Recently we just added 2 old heaters back onto the system ( these are original heaters back to there original locations) now we are getting a ton of really loud angry knocks all over the house. Not just from the heaters that were reinstalled. Any ideas?

On 2017-01-17 02:30:15.375762 by Will

Well, my air is back again.
I've purged many times, replaced both the automatic vents, replaced the pressure relief valve, have no visible leaks anywhere and yet I still get air in my heating. The bucket under the relief valve is dry so it's not releasing water there. I have a Watts SB1156F pressure reducing valve with the autofill bypass lever on top. I was told that I could remove the cap and push rod and screw clockwise to increase the output pressure from 15psi to something slightly higher.

So, thinking that I wasn't getting enough output from the Watts I tried that. I turned it a quarter turn and immediately water started coming up from the screw head and out through the top of the valve where the override lever screws on.

Assuming this is a bad thing I put it back to where it was and the water stopped. My thought is that the Watts is faulty and not actually refilling correctly. However, when the system was empty for the pressure relief valve repair, when I went to refill the system I left the valve on automatic fill and I could hear the water filling the system until it reached operating pressure which the gauge on the boiler said was about 15psi...

.so it works, I just don't know for certain how much pressure it's providing based just on a notoriously inaccurate gauge. This is infuriating.
One more thing, when I do get air in the system it seems like it's suddenly very noticeable. Not a slow increase in air, just a lot of air suddenly. Not enough to become air-bound but I'm worried that if I leave it for a day or two that will happen and being in New England in January....it's a bit cold outside ;-)
Frozen pipes are all I need....

About two years ago a plumber replaced the expansion tank, is there a right way and wrong way to replace one ? I'm wondering if that's it since I feel like I've addressed everything else short of replacing the reducing valve (Watts). The tank is warm at the top and cool at the bottom so I know it's not full of water, I just wonder if the pressure is wrong or some other issue that may be caused by a mistake during the installation.

I don't know, just trying to get to the bottom of this. If I test the pressure on the tank and the heating is hot what should it be ? Would it be higher/lower/equal to the normal pressure of (I think) 15psi when installed due to the heat in the water above ?

FWIW, I asked my plumber and his only suggestion was to install a scoop for about $800 but told me that that might not make any difference. I trust his judgement but his last "repair" was to purge the air and it came back 2 days later. I have since replaced the parts I mentioned above to no avail.

On 2017-01-14 01:12:42.059433 by (mod) -

Fran

Please search InspectApedia.com for WATER HAMMER NOISE to see what's probably the problem. Your plumber can install an anti-water hammer device or change out a too-fast-closing valve if that's confirmed to be the trouble.

On 2017-01-12 00:57:59.851359 by Fran

I have a Utica gas hot water base board heating system. It is making a loud bang followed by rattling in the pipes. A repairman replaced the thermostat but the sound is still occurring every 30 to 60 minutes in different rooms.

All baseboards appear to be working but it sounds like the house is going to explode. The repairman had no other suggestions. I opened the release Valve by the boiler and no air came out, just water. Can you help me?

On 2017-01-09 02:39:01.601489 by (mod) -

Very good question. Whether or not you can bleed a single length of baseboard depends on where air bleeder valves are located. For example if you check the ends of runs of baseboard in your home you may find that some but not all of them have air bleeders installed.

If the cold section of baseboard does not have an air bleeder installed it still may be possible to push the air out of that section of heat piping by opening the bleeder valve anywhere on the piping Loop that is higher than the cold section.

This article series includes two different approaches to correcting an Airbound heating system. One of them involves opening bleeders the other involves increasing the boiler operating pressure briefly and pushing water at higher pressure through the heating piping to force trapped air out. You can read both of those methods in this article series

On 2017-01-08 18:33:05.021323 by Cheryl Martina

I have a boiler system and I am not getting heat to all my baseboards am I able just to bleed 1 baseboard and clear the air from the pipes. Only 1 baseboard is cold and its been silent. I bled the air from a different baseboard and now the baseboard that was cold is making clicking noises.

On 2017-01-06 22:59:27.758998 by (mod) -

Anon:

Some boilers use only a manual re-fill valve;
But more often, the pressure-reducer valve is treated as an automatic water feeder even though the manufacturer says (CYA) not to rely on that feature.

I recently removed a pressure-reducer-feeder that we discovered was totally blocked - it wasn't feeding at all. Nobody noticed the problem for years until finally the boiler leaked enough to lead one of the heating zones to become airbound.

On servicing the old style bladderless expansion tank we drained the tank then observed that when we turned the water valve back on no water entered the boiler nor tank. We replaced the pressure reducer.

If you search InspectApedia.com for AIR BOUND HEATING SYSTEM you'll see a couple of methods for forcing troublesome air out of the piping when simple bleeder valves aren't doing the trick.

On 2017-01-06 14:27:00.484376 by Anonymous

Forgot to add.....if the relief valve is leaking or letting water out, why isn't the auto fill replenishing it ?

On 2017-01-06 14:25:26.864430 by Anonymous

I've had a plumber come and remove the air and it still returns within 48 hours. He also closed off the automatic bleeders to prevent the possibility of air being sucked in through those.
Maybe worth mentioning.......

the boiler pressure relief valve is producing water, not dripping but there must be occasions where it either opens or leaks because the bucket beneath it is collecting water. After my plumber last removed the air he also emptied the bucket. Within 48 hours there was air in the pipes again. Using the auto fill valve I refilled the system by popping the lever on the top of the auto fill for 3 seconds.

After doing that the sound of air in the pipes was almost gone. 3 seconds of city pressure is roughly equivalent to the amount of water that had collected in the bucket under the relief valve.....coincidence ?

Also, with me using the autofill valve "wide open" - where did the air go ? The bleeders are still closed.
The top half of my expansion tank is warm, the bottom is cool so I assume that's ok. It's only 2 years old.

The running PSI is about 24 which I realize is higher than normal. If I lower it to 15 won't I just get even more air in more quickly ?
It's driving me nuts and I'm trying to sell the house.....I really don't want to have to disclose that the heating isn't working properly...need to fix it !

On 2017-01-04 20:23:42.517796 by (mod) -

Betty

Typically there has been spillage, debris, or even a dead animal on the baseboard. That is, the odor won't be from the heating water itself unless there is a leak.

On 2017-01-04 17:24:25.824222 by betty

Why is there a fume coming from baseboard radiator when heat is coming in

On 2016-12-15 19:40:56.936747 by Patch

I have been trying to bleed air out of a baseboard heater. As soon as I get it to 78° and come back a half hour the temperature has dropped again and I get hot water out of the bleeder and a lot of air and I have been on this for 4 hours now. The thermostat is new, the zone valves are all new. But the third floor apartment below has all kind of heat? HELP

On 2016-12-12 23:52:02.044652 by kathy

The heat in my house is staying downstairs i bleed all the radiators but none of the ones upstairs are receiving any water or heat but they did at first when heat was turned on what am I missing

On 2016-12-11 03:48:23.546816 by (mod) -

I suspect that either they are not bleeding out all of the air, or there is a leak in the system that is admitting air.

On 2016-12-10 19:31:00.889870 by Nicholas

Hi, my apartment has 2 radiators on the same wall that are never warm. Landlord sends repair guys to fix it but they just bleed those 2 radiators and say its fixed. Heat MAY come out for 30 mins and its completely gone. What is going on here? (Its been like this for 2 1/2 years now) seems like this requires more than bleeding air out after 10+ attempts

On 2016-10-30 21:12:15.494413 by Will

(Feb 19, 2016) danjoefriedman (mod) said:
I suspect that either you are not getting all of the air out of the piping system, or there is an air leak into the system, perhaps at one of your air bleeder valves.

I have the same issue, I bleed the zones and after a few days they have air in them again, this goes on and on all heating season. Assuming I don't have leaks elsewhere could the two bleeder valves be allowing air into the system ?
What would happen if I bled the system, got all the air out and closed the bleeders. Would it over pressurize and pop the relief valve ? I'm not sure I want that to happen while I'm not at home...

I currently bleed the zones using shut off valves on the return side and push fresh water through the zones to purge the air through spigots just in front of the shut off valves.

My system looks something like.....

Boiler
Zone valves
Bleeders
Radiators
Spigots
Shut off valves
Circulator
Boiler

Replacing the bleeders seems like the easiest thing to try but I don't want to open up plumbing if I'm wasting my time....


Thanks.

On 2016-10-29 00:10:30.913452 by (mod) -

Some,

Glad it worked for you.

On 2016-10-28 23:15:32.766510 by SomeDude

Thank you for all the information! Just fixed my system following these methods.

On 2016-03-13 04:11:19.837176 by (mod) -

Zac

If the system is NOT air bound somewhere, you should feel the pipes warming up in a few minutes after the circulator starts - longer for very long piping runs. If not, start at the boiler and follow the piping to find where it's cold. That may be an air-bound section.

On 2016-03-11 06:03:09.273146 by Zac

I found bleeders on the base boards them selfs I have bleed them till water was steadily coming out now how long will it take for that water in those pipes to heat up?

On 2016-03-11 04:55:58.737113 by Zac

I have what looks like a bleeder on one line an a pressure pull in one pipe best way to explain it that lets water out but no were I see has a spot to connect a hose I'll give it a shot an let you know

On 2016-03-11 03:50:09.857593 by (mod) -

Zac,

Perhaps you need to add water and bleed air from your heating system.

On 2016-03-10 21:44:26.094402 by Zac taylor

I changed an adapter that connected the hot water baseboard pipes together in my lower level the other day an a lot of water came out now that it's back together it won't hear the same level as what it is on but will the lower level why

On 2016-02-19 22:56:16.614585 by (mod) -

I suspect that either you are not getting all of the air out of the piping system, or there is an air leak into the system, perhaps at one of your air bleeder valves.

On 2016-02-19 20:11:12.997574 by Kevin

My baseboards keeps getting air in it, Usually a day or two after I bleed the system. What should i do?

On 2016-02-16 18:16:45.820277 by (mod) -

Sure Robert. in this article you'll find a live link to exactly what you need - see

Continue reading at AIR BOUND HEAT SYSTEM REPAIR by PUMP

On 2016-02-16 16:57:07.786291 by Robert Smith

I have a 4 zone boiler radiator system. Each zone has it's own circulator pump, thermostat, and control unit. The boiler and three of the zones are heating and one zone is not. For that zone, the thermostat is calling for heat and the circulator pump is running.

I suspect the zone is air-bound. I have no air-bleed valves on any of the zones (baseboard radiators) but the system does have a water spigot installed on the supply side of each zone after the flow control valve and another identical spigot on the return side of each zone just before the circulator pumps and common return manifold. Both spigots have garden hose connectors. I also have a conveniently located floor drain.

Can I bleed the zone by attaching a garden hose to the supply side and another garden hose to the return side, turn on the water and open the valves? Do you see any problem with this or is it time to call a service rep?
Thanks, Robert

On 2016-02-14 18:33:15.069949 by (mod) -

Jim as you have only one circulator and one piping that branches into two sub loops, it sounds as if the circulator works and thus your cold downstairs must be due to a blockage, usually air. Feel along the pipes following them until you feel where the temperature drops off.

You may need to use the procedure cited at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE

Or at AIR BOUND HEAT SYSTEM REPAIR by PUMP

On 2016-02-14 18:20:37.110193 by JIM

The other day my oil fired hot water system acted up. The furnace itself is operating fine the system is single zone and splits to go upstairs and downstairs and rejoins at the end of the system to go into the circulating pump.

The pump is fine and the upstairs feed gets very hot but the downstairs stays cold. I bled the system found no air. I then drained the entire system and refilled it and bled all the air out but it's still cold. I bled the downstairs system at all 3 points. I get plenty of water out of the bleeders so i know there is no blockage. Any thoughts?

On 2016-02-13 16:59:32.654519 by (mod) -

Sure Dennis

See https://inspectapedia.com/heat/Boiler_Expansion_Tank_Drain_Procedure.php

On 2016-02-13 15:05:55.218978 by Dennis

I have bled my hot water baseboard heaters successfully, but I have what appears to be a pressure tank on my oil fired furnace. I think I recall that the tank should be empty. By weight, it feels like there is water in it. How do I properly remove the water from the tank? Just open the hose bib valve??

On 2016-01-17 21:05:04.075027 by ed Breimann

Thanks Dan.

On 2016-01-16 18:02:02.942802 by (mod) -

Parnell

Turn off the boiler immediately .

Look for the soothe of water, that will tell us what's wrong.

On 2016-01-16 14:58:04.307601 by (mod) -

Ed

Your system may be partly air bound

On 2016-01-15 22:05:39.610557 by ed Breimann

I have a one zone hot water baseboard system in my apartment. Don't know where the supply and return lines are situated. The liv. room section is cold while the bedrms. are hot. How can this be in a single closed loop? Thanks.

On 2016-01-15 11:32:13.856594 by Parnell

What does it mean when all the water runs out the bottom off you boiler

On 2015-12-29 14:57:35.797032 by (mod) -

Your boiler pressure is abnormally high. Search InspectApedia.com for CAUSES of RELIEF VALVE LEAKS to see the most likely causes. The drop in temperature in the boiler at the start of a heating cycle is normal as cold water is returning to the heating unit from cool baseboards, radiators, or piping.

On 2015-12-29 13:50:39.905116 by Neil

My hot water boiler is not working correctly. High temp is set at 180, pressure is to high, 30 psi. I put in new expan. tank. If temp in boiler is 175 then circulator comes on temp does not go down much but when boiler starts within 60 second a 30 degree drop in temp. Do I have an air block or is circulator bad?

...

Continue reading at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Articles on Fixing Air-Bound Heatiing Systems

• AIR BLEEDER VALVES
• AIR-BOUND HEATING SYSTEMS - home
  • AIR BOUND RADIANT HEAT
  • AIR BOUND HEAT SYSTEM REPAIR by PUMP
  • AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
• AIR SCOOPS PURGERS SEPARATORS

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AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING RADIATORS

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