Hydronic heating constantly becoming airbound

cujo

I'm a new homeowner in need of advice. I just had a new boiler installed and had them back 3 times to purge the air. I think they got all the air out from the install but it keeps coming back. Here's the full story:

Last winter was my 1st in this 1956 house. I had some air problems and excessive expansion noises. But I never noticed a pressure reduction. The boiler was ancient and I had it replaced early October just to be proactive (replaced oil boiler with gas, no changes to baseboard radiators). I immediately noticed a severe air problem, much worse than before.

My house is a split level with 2 zones. I never notice air on the lower zone only the upper zone and mostly in a bedroom that is slightly higher than the rest, as it was an addition.

They purged the system 3 times and the last time it was silent when 1st turned back on but gurgling started again and became loud within a few days. I have one upstairs radiator vent that I've been bleeding about once a week. I keep it open with minimal water dripping while the zone is calling for heat and I can hear air intermittently coming out. The air especially comes out when I hear gurgling. After I stop hearing air for a while, I close the vent.

I noticed the pressure dropped a few psi over the past couple of weeks. I'm not sure if that's due to me bleeding it from the upstairs vent or if there's a leak.

I've searched for leaks but I don't see any signs on the radiators, pipes, floors, or ceilings. Not sure if it's a pinhole leak that evaporates and let's in air after it cools. I also have pipes running through the slab but that is on the lower zone that I don't have a problem with.

The gurgling gets bad enough to wake me at times but I'm more concerned about corroding the pipes or stressing the circ with large air pockets.

So after researching this and finding some good info on this site, there's two main things about the install that concern me:

1) They configured the circulator pump on the return side flowing towards the expansion tank. I mentioned this to them but they shrugged it off saying they've installed thousands of systems this way.

2) They didn't install an air scoop, just a Hy vent. They replaced the Hy vent the last time they purged and said it was clogged. But they are extremely hesitant to install an air scoop for some reason.

Could anyone recommend good advice on how I should proceed? Is it reasonable to ask them to reconfigure the piping? Should I buy "Pumping away" and show this to them as a reference?

If I can't get this fixed, how much damage could this cause by me purging air every week and restoring the pressure loss as needed?

I attached a photo. The upstairs zone has two return pipes. Thanks in advance for any advice!

JUGHNE

It has happened that the air vent could be sucking air in when the pump runs.
You could screw down the cap tightly on the air vent then vent all the air you can. Some heat the system up to temp then shut burner and pump down. I would manually open the zone valves with the lever on the bottom of each. Let sit at least 30 minutes, air may go to the top of system to be bled out of your BB's.

When you think you have all the air out you could turn things back on but keep the air vent sealed. See if anything changes.
Keep an eye on the pressure gauge.

cujo

Thanks, I'll give this a try.

hot_rod

All systems need an air purger in my opinion. A hy vent alone will not remove the bubbles, especially micro bubbles that form in a system. The name alone should be the clue, they are intended for high point air removal.

Every time you bleed you add freshwater, within that fresh water is additional air, plus you are adding minerals into the system with every new water, not advisable on any system. Mineral deposits inside the boiler reduce efficiency.

Many of the mod con boilers prefer to pump on the return pumping into the boiler, so that is not a deal breaker.
But the expansion tank still needs to be near the inlet of the circulator, air purger at the supply connection out of the boiler.

Be cheaper for them to install an air purger instead of all the return service calls, one would think?

Nice looking piping, however.

cujo

I agree that it would've been a lot cheaper for them to install the air purger. I'm not sure why they are so hesitant.

If they move the tank to the inlet side of the circulator would they also need to move the zone valves to the other side to prevent them from being slammed by the circulator pressure when they shut off?

hot_rod

Two fairly easy fixes, there is a plug at the end of the header below zone 1 return, the expansion tank could easily go there with a
1-1/4 X 1/2 ell and a couple nipples.

Looks like room to install a threaded air separator to the right of the Taco LWC with a couple nipples. Use a good micro bubble remover Spiro, Caleffi, etc, not the cast iron, camel hump type.

Gordy

If they would have put the circulator on the supply just above the x tank connection it would enhance air removal. Also a better air removal device as @hot rod_7 noted.

You also have to remember that a fresh oxygenated water start in a complete system from a repair, or installation will require the system to release the oxygen from the fresh fill water.

Raising system temps for a while helps release that entrained oxygen. Then drop temps back down to normal. This is a step pointed out in some vintage boiler installation manuals.

JUGHNE

Closing that HY-vent cap is not a permanent fix.
BTW, if it still has a small vent hole in the cap, you could replace it with any bicycle tube cap for a solid seal.

However this may indicate the source of why you are gaining air as the system runs.

Alan (California Radiant) Forbes

Sorry to sidetrack this thread, but I have a stupid question:

How much air will come out of a newly filled system, let's say 20 gallons. You've purged all the bubbly air out and just have new water. Is there a formula to figure this out?

Gilmorrie

What is the system pressure and temp? What is the white tank in the upper-left of the photo?

cujo

@Gilmorie I lowered the temperature to 168°F from 180 a few weeks ago because I was thinking a lower temperature would help with the expansion noise and maybe even with the air.

The pressure is about 16 psi. I don't see much change when cold or hot.

The white tank in the upper left is for the water heater, not connected to the boiler.

Zman

I would fall back on the I&O manual. If they piped it per page 7, you would not be having this issue.

cujo

@hot rod_7 thanks for those recommendations. If I were to move the tank to the inlet side of the circulator, would the zone valves get slammed with water pressure when they turn off?

cujo

@Gordy thanks the the info. I actually lowered the temperature to reduce expansion noise a few days after the installation. The previous home owners had it set even lower with the old boiler and I thought they might have done it for that reason.

After reading your comment, I'm thinking about raising it temporarily while bleeding the air from the upstairs radiator.

How long does air come out of the water? It's been several weeks set at 168°F.

hot_rod

Alan (California Radiant) Forbes said:

Sorry to sidetrack this thread, but I have a stupid question:

How much air will come out of a newly filled system, let's say 20 gallons. You've purged all the bubbly air out and just have new water. Is there a formula to figure this out?

The Amtrol handbook has a lot of info on air and the ability of water to hold air.

Some air enters with fill water, they studied several locations to come up with 2%.

There are different way air is in the system.

Bubbles which we typically manually purge out.

Entrained air which moves with the water, this is what most people hear and complain about.

Air in solution which comes out as temperature increases. It has to do with pressure and temperature.

The second two are the reason a good air purger capable of capturing and removing air is so important, it tough to manually purge that out, especially when you keep adding cold fill water

There really isn't much of a mechanism on float (hy vents) to grab that entrained air, some have a small tab to try and grab some bubbles, but they are not intended to be an air purger.

Gordy

You must understand cold fill water say 50* holds more air than say 180* water. So the battle is getting the entrained air out a little at a time as the system goes up, and down during a heating cycle.

By raising the complete system temp to a little higher than normal operating temp for an hour. You are releasing the entrained air faster.

Gordy

No I don’t know of a set formula. I’m quite sure there are tables for how much oxygen is in 50 verse 180 water though.

hot_rod

After a short period of time you are actually dealing with nitrogen in the system, O2 will oxidize any ferrous components and be gone. Air is 78% nitrogen around 20% O2 and some other inert gasses. Unless you live in some of those smoggy cities in China

Remove a circulator two days after you install it and see a reddish or grey color to the cast, it was oxidized by the contact with O2 and consumed the oxygen in the process.

Now with non barrier pex, thing change.

Gordy

Here is a chart for fish, but the principle is the same. Note the right hand columns on how much dissolved oxygen distilled water can hold at various temps. From 0-30 degrees Celsius the amount of oxygen saturation decrease.

Gordy

So from 32 f to 86 f .

hot_rod

Boyles law of perfect gasses, Holohan has been pounding this into our heads for a few decades now. Remember his soda bottle trick?

Again, download the Amtrol Engineering Handbook they have all sorts of charts, formulas and math to keep you learning.

Gordy

hot rod_7 said:

After a short period of time you are actually dealing with nitrogen in the system, O2 will oxidize any ferrous components and be gone. Air is 78% nitrogen around 20% O2 and some other inert gasses. Unless you live in some of those smoggy cities in China

Remove a circulator two days after you install it and see a reddish or grey color to the cast, it was oxidized by the contact with O2 and consumed the oxygen in the process.

Now with non barrier pex, thing change.

For all intensive purposes to avoid starting chemistry class I referred to air in the system. As to not be to confusing to the OP yes the oxygen is absorbed by the ferrous components, but that leaves 80% other gases in the system

hot_rod

Gordy said:

hot rod_7 said:

After a short period of time you are actually dealing with nitrogen in the system, O2 will oxidize any ferrous components and be gone. Air is 78% nitrogen around 20% O2 and some other inert gasses. Unless you live in some of those smoggy cities in China

Remove a circulator two days after you install it and see a reddish or grey color to the cast, it was oxidized by the contact with O2 and consumed the oxygen in the process.

Now with non barrier pex, thing change.

For all intensive purposes to avoid starting chemistry class I referred to air in the system. As to not be to confusing to the OP yes the oxygen is absorbed by the ferrous components, but that leaves 80% other gases in the system

Agreed, he just needs whatever is in there, out.

If the installer keeps doing what he's been doing, he will keep getting what he's got. An air problem. Might be time to shop for another?

cujo

@JUGHNE just wanted to follow up and let you know your suggestion worked! I thought it was a long shot since the installer replaced the air vent and I was still getting the same problem. But the air problem seems completely gone after closing the vent, increasing the temperature to 180F, bleeding the air from the upstairs radiator, then lowering the temperature to 175F. It's been a few days since I touched it and no signs of air coming back into the system. The only noises now are due to expansion. Thanks again.

EBEBRATT-Ed

I would suggest moving the circulator and adding an air scoop at some point even if you do it next summer.

Systems with high restriction don't do well with pumps pumping toward the expansion tank. You can pull the return into a negative and pull air in as you were doing. @Jughne suspected that. Systems with low restriction can usually get away with the pumps on the return although the supply is always better.

Solid_Fuel_Man

Also raising the pressure while pumping toward the expansion tank can be a band-aid. Also need to air up the tank to match that water pressure before increasing water pressure. Keeps the pressure positive on the inlet of the circulator.