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Rick, Construction Supervisor
Category: Plumbing
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Experience:  Licensed Master plumber with 40+ yrs. experience.
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How to get air out of baseboard hot water heating system

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How to get air out of baseboard hot water heating system

Welcome to Just Answer. I will do my best to fully answer your question(s).


You are doing exactly what needs to be done. Sounds like you are having difficulty, however, be patient, this may take a day or two to remove ALL the air. If you are still having issues after a few days, I suspect air is getting into the system from somewhere else. Perhaps the bladder on your expansion tank has a small leak? however that air also would eventually disappear after bleeding ALL the units a few times. cranking up the heat temp in the home for a bit will get things moving faster as well.

Customer: replied 5 years ago.
Can you be more specific? The bleeding wasn't working. Here is more information. I was able to get water flowing okay from the smallest zone on the 1st floor above the basement. Then I tried the top floor zone. Hot water was coming up to the top floor but then stopped. I went to the basement. The boiler was cycling on and off. I think the problem was that the water circulator motor was off I assume because it is thermally protected. Everything was getting too hot because there was so much air in the system it couldn't circulate. The reason there is so much air in the system is that during the summer I had the main on/off valve for the water coming into the house from the street replaced. I decided to turn down the thermostats and get expert advice.
The layout is like this. It is a 3 zone system. There are two pipes above the expansion tank. Each pipe then branches into two pipes. There are electronic valves in each pipe above one of the branches. There is an electronic valve below the branch in the other pipe. Each of the 4 pipes (two from each branch) has a spigot with a wheel-type open-close and it is threaded so I could attach a hose.

If you are able to determine which line(s) make up the return side of the system, I would attach a hose to those drain valves and open one at a time with the system all on and the zones calling for heat (temp control up above existing room temp). Also have the fill valve for your sytem open so you continue to feed water until all the air is out. To verify that the air is out, once you think its mostly gone. Place the hose into a half full bucket of water and comtinue draining the line. If you dont see any more bubbles in the water you have released all the air from that zone. Do the same procedure with all the zones.

Customer: replied 5 years ago.
How do I identify the return lines? Also, do I turn up the thermostats in all zones at once or only for the zone I'm trying to purge? I'm uncertain about that because you said to to attach a hose to drain valves and "open one at a time.". I assume the drain valves you mean are those spigots I said were in each of the 4 pipes going up. Is that correct?
After I wrote the above I went and looked at my system. I do not believe any of the 4 pipes with the spigots on them are return lines so your last answer won't work. I see 3 pipes joining right before my circulator motor. Only one big pipe comes out of the circulator motor and that pipe goes back to the boiler. There is a spigot in the line between the circulator and the boiler but it is not threaded so I can't put a hose on it (and it faces upward).
Yes that is correct about the spigots. The return lines should first of all not be as hot as the supply lines and also this should be the lines that DO NOT have individual zone valves on them. Another way would be to look at your pump (recirculator) this should always be installed on the return line side of the boiler system so that should help you. As for the temperature, go ahead and turn all the zones up, you wont hurt anything.
Customer: replied 5 years ago.
Did you see the second paragraph of my last question? I said the 3 return lines going into the circulator and coming out of the circulator and going into the boiler do not have threaded spigots. I think all 4 of those spigots above the electronic valves are in hot water output lines. There is no way that I can see to tap into the return lines. Can you stay with me until we're done? This dialog has been going on for an hour.
so nowhere on your return lines has a drain valve that you can identify? sorry this is taking so long.
Customer: replied 5 years ago.
No. As I said, there is only ony valve between the circulator (above which three lines come together) and the boiler. The outlet faces upward and it is not threaded so it does not appear to be intended as a drain. I certainly can't attach a hose to it.
I apologize that this is taking so long for you. Unfortunately I am going to have to refer you to another expert on the site as i cannot stay on any longer myself today. after this post to you I will be OPT-ing OUT and refering your question to another expert. Thank you for your patience.
Customer: replied 5 years ago.
I think that's a good idea. You may not be familiar with the piping arrangement I havedescribed. Thanks anyhow
Welcome to Just Answer,
The following instructions are for a typical hot water config which it sounds like you have. If you have any more questions after reading this let me know.

A purge station is typically a shut off with a hose fitting above it. There can be 1 piece purge stations where both the shut off and hose fitting are combined in one piece. Or it can be a separate valve(shutoff) with a hose type "faucet" (we call it a boiler drain) above it. They are usually at the boiler on the pipe above the circulator pump. You need to determine which one goes to your problem area. I have seen them in old systems some distance from the boiler on the heating line (pipe). You need to shut the valve attach a hose to the hose fitting then open the hose "faucet". Some all-in-one fittings close the valve and open the hose at the same time so be sure your hose is attached first if you have one of these fittings. If you have zone valves with multiple purge stations all the zone valves should be opened manually. If you have zone valves and only 1 purge station then you need to open the zone valves one at a time and fully purge a zone before opening the next valve and closing the valve you just purged. You also need to jack up the pressure while you are doing this but you need to keep the pressure under 30 psi. This is done by increasing the pressure at the feed (pressure reducing) valve. Some types have a lever that you flip up from a "horizontal" position to straight up. This is the easiest type to use. Some require that you tighten the screw at the top of the valve. You should be warned that if this valve hasn't been touched in a while disturbing it in this manner can cause it to fail in which case it will need to be replaced. This device is located on the water supply line to the boiler. Be sure to turn the power off to the boiler while you are doing this. When you hear no more bubbles coming out of the hose for several minutes you shut the hose off at the same time you return the feed valve back to it's original position. Then open the shutoff. Be sure the pressure on the boiler is between 10 & 15 psi when you are done before you turn the power back on. The boiler you have has no bearing on this process. It is the same what ever type you have. Having said all that this is not something I would recommend that you try yourself unless you feel very confident about doing it. You may have to call a plumber anyway if the feed valve fails.

Customer: replied 5 years ago.
You said the purge valves are "usually at the the boiler on the pipe above the circulator pump. Please read all of my information again. There are no valves above the circulator pump. The circulator pump is in the retun line. Three pipes join, go into the circulator pump, come out in a big pipe and go to the boiler. Read where I said there are spigots in all 4 pipes above the electronic vales that are in the pipes coming out of the expansion tank. These spigots appear to be in the output from the boiler, not the returns. Are these the purge valves you are talking about? Do I open them with the heating system cold and off or with the heating system on and the thermostat turned up to open the electronic valve. Can you stay with this question. I worked with another of your experts for well over an hour because he took 15 minutes to reply and he finally gave up. I don't think he was familiar with my type of system or he could not visualize what I was explaining. I'm not willing to keep up this dialog if it takes 15 minutes to get a reply.
OK, you set up is atypical but the principle outlined in my directions still apply. The only difference is that it sounds like your purge stations are on the supply not the return. You need to be sure the zone valves are closed. Then purge each zone one at a time. Once all the air bubbles have stopped you need to open the zone valve that corresponds to the zone you are purging and let the air out that is trapped behind the zone valve. You should be able to manually open the zone valves without turning up the thermostat
Customer: replied 5 years ago.
Is the heating system to be turned off during this operation? If not, how can I know the zone valve is closed. After the air bubbles stop, to let the air out that is trapped behind the zone valve, you say to open the zone valve. I'd have to turn on the heat and raise the thermostat to do that wouldn't I? Sorry I'm so stupid about these matters but I can follow step by step directions. How would I know when the air trappped behind the zone valve is gone? Hot water would be coming out the hose.
The system should be off when you do this. You should be able to manually open the zone valves (there are a few exceptions). If you can't manually open the valves then you will need to turn up the thermostat to open them. If you can't figure out how to open the valves then describe them to me or give me a brand name. Of course the power will need to be turned back on for the valves to open if you can't do it manually. You know the air is gone when there are no more bubbles coming out of the hose. You should let the water run for several minutes after the bubbles stop to be sure. Once you purge the entire system turn up each zone on at a time and listen for air. If you still have some air you repeat the procedure. You're not stupid, this procedure is a bit involved and also a bit difficult to describe. It's second nature for me but for someone who has never done it before it can be confusing.
I'm taking a break now. If you have any more questions I'll respond when I get back. If not please hit accept. Thanks
Customer: replied 5 years ago.
The electronic valves are Honeywell V8043F1036. I took the case of one. Unless I would actually remove the whole electronic box, I don't think I can manually open it. In the meantime while waiting for replies I have been trying to bleed it through the bleeder valves. There is one in each zone in the radiator pipe that runs along the floor of each floor(zone).
You can easily open this valve. If you look at one end of the valve head you will see a lever in a slot. The slot will be embossed with AUTO at one end and MANUAL at the other. You just move the lever to manual and hook it into the little notch so the lever doesn't move back to auto on its own.
Customer: replied 5 years ago.
I took the cover off one. On the left side tucked in so I could not read the embossing to which you referred there is a small, thin brass piece attached to a spring. The brass piece is vertical. To turn it to manual would I slip my finger under the bottom and rotate the bottom away from the box until it is horizontal? Or do I rotate it 180 degrees so it's vertical again? And do I do this from the bottom as I suppose or grasp it at the top to rotate it?
Here is the manual, the lever is shown on page 3 and again on page 5
Customer: replied 5 years ago.
Hi Rick,
I've taken enough of your time so I'm going to accept your answer the next time you reply no matter what you reply. I've followed all that you said but I don't see how it can work. Here's what I understand you told me. I turn off the power to the system, manually open all 3 of the zone valves, and I increase the pressure by flipping the pressure reducing valve up. The increased pressure will force water from that valve through the boiler, up toward the boiler outlet pipes. The water will flow through all three zones at once. The hose will be attached to one of the 4 spigots that are immediately above the 3 zone valves. It seems to me that as soon as I open that spigot the water will come out of that hose. Since the path of the water is from the reducing valve, to the boiler, to the open zone valves, the water coming out of the spigot is coming from the boiler without passing through the radiator pipes on the floors above. Help me because I must be missing something. I understood how this would work if the spigots were in the return lines but not how it can work if in the outlet lines. Thanks. Tom
You almost have the idea. The misunderstanding lies in the fact that you don't open all zones at once. In your case you keep the zone valve closed while you purge. If my picture of your system is correct the zone valve is between the boiler and the hose faucet. This forces the water through the zone and the air along with it then out the hose. Only after you have finished purging a zone do you open the zone valve to get rid of any air trapped behind the zone valve. Like I said before your set up is not typical and not the best config but purging with the valves closed should still work.
Customer: replied 5 years ago.
I said I would not reply again but your last answer causes me to ask 3 more questions.
1. You are correct that the zone valves are between the boiler and the spigots which are threaded to receive a hose. You say that I "keep the zone valve closed while you purge" and "this forces the water through the zone and the air with it". If the zone valve is closed, how can the water circulate through the zone and the air along with it then out the hose?
2. Also, on each side of my boiler (outlet and return) there is a valve with wheel-type handles to open them. These valves are identical. They valves have a very short circular "pipe" about 7/8 inside diameter and about 1 inch high that faces upward. These protrutions are not threaded. Looking into them one sees a ring that is slightly smaller than the inside diameer of the "pipe". Immediately below that ring is solid metal that blocks the hole. The wheeel-type handle is horizontal (the "pipe" is vertical) so it looks like if one turned the handle counter clockwise, the metal plugging the pipe outlet would slide horizontally to open the outlet. The valve in the return line sits right on top of the junction of the cold water inlet from the reducer and the one pipe coming from the circulator motor where the three zone return lines have joined. If these outlets were threaded, I'd think they were for purging but they are not threaded. I think if I opened them, water would shoot up into the air. What do you think the purpose of those valves are?
3. At the base of my boiler, (about 4 inches from the bottom) there is a threaded spigot. Do you think that can be used to purge? For example, if I turned up all of the thermostats,hot water could flow through all zones at once and if I opened the spigot at the base, water would flow and maybe the air with it. Any thoughts on that?
The water is forced through the zone through the return then out the hose bibb (faucet) on your supply manifold. This is moving the water in the opposite direction of normal flow. This is the problem with how your system is piped but it should still work. I have no idea what you are describing on #2 but it doesn't sound related to purging your system. #3 describes the boiler drain, that is it's only purpose.
Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 19100
Experience: Licensed Master plumber with 40+ yrs. experience.
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