Air Getting into New Radiant System After Cool Down

danwheeler

Hi all,

I've got a new radiant system in new construction that I'm having a heck of a time with air in the system. I've been reading tons of info from posts on here and Garage Journal trying to figure out what's going on. I got the kit from a company who has been great but I'm always up for more information or ideas so I decided to post here. I'm very technically minded but a total newbie at radiant hydronic. Here goes...

The System:
This is a small system - one zone, one pump, 3 circuits, 600 feet of tubing in a concrete slab. "Cabin" is 650 sq feet. It's a pretty standard system, a Grundfos pump, Electro Mini boiler, Watts air separator, expansion tank at 20PSI, etc. I've used all Sharkbite connectors and regular (non OB) PEX on the wall which I know is not ideal but I don't suspect it's contributing to my issue.

The Setup:
My well water is a bit dirty and I haven't used it since summer so I've been using a sump pump to purge and charge the system. I initially purged the lines clean with very clean river water in a tub then replaced that with Cryotek premix antifreeze using the sump pump. I go through a purging process on each circuit and get all the air out to the point where it's completely silent and no indication of air in the system.

The Problem:
With system cold, (or warm since I've been able to reproduce this a few times over the last few days) and to the best of my knowledge, all air out of the lines, I fire up the system and it starts heating up. Everything is going as expected but the pressure starts rising up to 30PSI. I'm told this is bad and will blow the pressure relief valve. So my instinct is to lower the pressure by opening a valve downstream of the pump to let some fluid out. This does lower the pressure but it continues to rise. So I let more out which lowers the pressure again. When I do this, the boiler gets angry and starts making bad noises. I assume it's boiling off or doing a tea kettle thing. Not good. If I'm feeling brave enough to not worry about destroying a brand new boiler, and the noise isn't too bad, I'll let it continue. Normally, it will get past this noise after a while once pressure and heat start rising again.

Now here's where the fun begins... when the system reaches its peak temperature or the boiler hits its setpoint, either the thermostat will click off or the boiler will cycle off. When this happens, my pressure gauge goes to zero as the system cools off. When I start it back up again, boom - I'm full of air and now I've got real issues with boiler noise and water noise running through the pipes. At this point, it's game over, I have to start from scratch again purging the air out with the sump pump.

I did read either here or Garage Journal that the air separators can suck in air if they are behind the circulator pump. I believe this was happening any time my circulator turned off. I was able to turn the circulator on and off multiple times with my ear up to the top of the air separator and here a short air noise every time the circulator clicked off. I closed the cap on the separator and it stopped doing this. I suspect it was pulling air in. This solved one issue which was that every time the circulator would cycle on/off, even when cold, I'd get a bunch of new air into the system. So I'm not a big fan of those things or at the very least, I need to be very careful about when I open the cap, maybe only when the circulator is not running to let out any captured air.

My kit supplier thinks I need to ditch the antifreeze and fill with regular water filled via my domestic supply. He thinks my sump pump filling, purging and charging process is what's introducing the air and the antifreeze is making it hard to get the air out via the purging process.

I'm not so sure... but I also have zero experience with radiant systems and experts are almost always right.

My theory, based on the fact that I go from perfect, with no air, to full of air only after a cool down and system stop and restart, is that when I let pressure out when it hits 30, I'm creating a negative pressure situation when it cools and then sucking air in through one of the relief valves.

Which begs the question - why does my pressure keep going up and up and up as it heats?

I'm kind of stumped at this point. I'm going to check the pressure in the expansion tank. It's supposed to be factory set at 20 but I never checked it.

I'm probably going to ditch the antifreeze today replace with well water just to satisfy my supplier's suggestions so I can continue troubleshooting with them.

Any other ideas? Thoughts? Suggestions?

Thanks in advance for any help

Dan

danwheeler

A picture of the system. The circulator is pumping DOWN into to 3 circuits on the left side.

Also, I have tried flipping that expansion tank down. I did get a little air out when I did this but at this point, I don't think there's any air in it and I'm leaving it down during all this troubleshooting.

hot_rod

Is the cap loosened on that air separator? Within a day it should remove all air, big, small, dissolved, entrained. As long as all circuits are purged and able to flow across it.

Sometimes cranking up the boiler temperature for a few hours will help with the last bit of air removal. The higher the temperature the easier for air to come out of solution.

Looks like large diameter pex? With 600' loops it should be 3/4"?

Need to get around 4 fps velocity thru the tube to move all the bubbles back to the purger. If it is a multi speed circulator, run it on it's highest speed for a bit, you should immediately hear air purge out, if it is a velocity, or lack of, problem.

danwheeler

Thanks, HotRod, I've tried with the cap loose and tight. Either way, I get new air into the system after a heating cycle and I *think* (but don't really know) it's coming in during cooldown because I can immediately hear air bubbles and water noises after, but not before, the system shuts down and starts back up.

Like I say, everything is great until I reach 30PSI, let out some water/pressure, then when the system cycles off and back on again, I've got major air problems. I can't let it continue to run like that or it'll burn up the boiler. I think it gets a LOT of air in it when this happens. I can hear it gurgling and wooshing through the system. After this happens, I've let it run for hours but it still can't get the air out. Maybe if I left it for days, the air separator would do its job but the problem is, all that air comes right back in an instant when the system shuts off hot and comes back on again. Wouldn't really be a long term solution.

danwheeler

I'm not sure what kind of pump it is. It is multi-speed. I've tried running at medium and high.

The pex in the floor is 5/8ths. I think there was some confusion about square footage. I was sent 3 rolls of 300 but only used 600. My circuit lengths are 194, 224 and 174.

Jamie Hall

How big is that expansion tank? Are you quite sure it's big enough? Let's assume then that it is. Unhappily, I don't see any good way to valve it off of the system, so... you may have to purge all over again. However, you need to disconnect it from the system (not just reduce system pressure to zero -- physically disconnect it) and make sure all the water is out of it. Then charge it through the Schrader valve to your desired system pressure -- and if this is a slab you don't need 20 psi. 12 psi will do, but you'll have to set your pressure reducing fill valve if you have one to that as well. Then reconnect it to the system and run through your purges.

If you are getting the kind of pressure swings you mention, the expansion tank simply isn't doing its job. Either set to the wrong pressure or simply failed.

HomerJSmith

What kind of expansion tank that you have and what is the air pressure charge on the bladder side? I suspect that the tank is a potable water tank and the air pressure is set at 45 psi? This would account for a rise in pressure in the sys. The air charge should be at 12 psi. I would check that.

The location of the air eliminator could be problematic and the pump could be pulling air into the sys. What size is the pump?

You are pumping away from the tank which is good.

Does the pressure gauge on the right side of the air eliminator show a drop in the reading when the pump turns on?

The photo is kind of dark and I would prefer more light on the subject.

danwheeler

hey guys, thanks a bunch for the help today, I really appreciate it. I just got back from the hardware store to get a tire pressure gauge. I'm kind of out in the sticks so my options are limited and I left my good gauge at home. I could only get one of those cheap gauges with the little white stick that shoots up. It was reading 22PSI. Yes, I think it's a domestic/potable expansion tank and it's supposed to be pre-charged to 20PSI. I'm at 1800' elevation so maybe that explains the 22.

I don't believe I have a pressure reducing fill valve. Just two hose-fill valves with a shut off between them. I get my initial pressure of 12PSI either by filling with the sump pump which happens to be able to pump to just about that pressure or from my domestic supply which will take it to 60 then I'll back it off by letting out some water.

There's a relief valve to the right of the gage which I'm told is set to 30. Then there's another relief valve to the right of the boiler that looks to be a standard hot water heater pressure safety valve. It's REALLY easy to pull the level on the hot water relief valve and let water out which makes me think it wouldn't take much for a little vacuum to pull in some air from there. But that's a total guess.

I'm not sure what size the expansion tank is. It looks about the size of a 1 gallon can of paint. I'm also not sure what size the pump is. I'm kind of useless huh? But I'll post some better pictures.

So right now I'm trying to decide between listening to my kit supplier and get rid of all the antifreeze and re-full/purge with straight water or try again with a lowered expansion tank pressure. And yes, I will definitely completely remove the expansion tank. I've already got a ton of air in the system so I have to re-purge everything all over again anyway.

Have you guys ever heard of a sump pump adding a bunch of air? As mentioned, the system SEEMS perfect to me once I purge all the air out until it heats up and cools down. But my kit supplier thinks my sump pump and too much antifreeze is introducing too much air initially into the system which is creating my unusual pressure increase (assuming because air expands more than water when it heats up?)

Jamie Hall

Several comments -- besides that your kit manufacturer isn't helping you any.

The expansion tank is the wrong type for a heating system and is too small. You need one designed for a heating system -- that one is domestic potable water (even says so on it). Now -- since you are on a well, had you not put the antifreeze in I'd say you could use it for your hot water. But, since you did, you can't, since antifreeeze is quite toxic and it would be hard to get rid of all of it.

So. Get yourself a proper heating system expansion tank, sized for the system. There are online calculators which will help you find out what you need.

Second, the antifreeze has nothing to do with the air getting into the system, nor with the pressure swings. If that's what your kit supplier is telling you, they are clueless.

Third, no a sump pump won't add air (with or without antifreeze). What adds air is the system pulling a vacuum when it cools down, sucking in air from wherever it can get it. Which goes back to the expansion tank being way too small.

danwheeler

thanks, Jamie - I used a few calculators and they all seem to point me towards a 2 gallon expansion tank. I believe the one I have is a 1 gallon? and it's set to 22 PSI.

Any ideas why the kit is not working as designed? I'm sure they sell thousands of these systems that work - why is mine different? Could it be because it's so small and there's no expansion capacity in the tubing itself?

Do you think it's worth trying to reduce the pressure on this 1 gallon expansion tank to see if it helps? I'm about 2 hours away from home so every time I work on this thing, it's 4 hours of driving so I try to accomplish as much as I can when I'm here.

I removed the expansion tank and discharged it completely. There's no water in it now. I bought a small bike pump at the local store and can charge it back up to 12PSI or as close as I can get with this cheap 10-50 PSI tire gage.

danwheeler

or... The Home Depot about an hour from here has a 2 gallon Everbilt expansion tank in stock for $40. I don't care about the $40, is it worth trying a 2 gallon tank to see if it solves the problem then buy a proper radiant X tank later? Is a potable different than a radiant? If so, how?

HomerJSmith

The correct tank would be Extrol #30 with an air charge of 12 psi. How do you fill the sys? Too, large a tank is ok, too small is very problematic.

https://www.supplyhouse.com/Amtrol-102-1-30-Extrol-EX-30-Expansion-Tank-4-4-Gallon-Volume

danwheeler

HomerJSmith said:

The correct tank would be Extrol #30 with an air charge of 12 psi. How do you fill the sys? Too, large a tank is ok, too small is very problematic.

thanks - wow that's enormous. I've been filling and purging the system with buckets, tubs and a submersible pump that I normally use for draining my hot tub. Initially I filled and purged the system with a big tub full of clean water pushing into another empty tub. I have two hose valves with a shutoff valve between them so I close the shutoff valve, pump into the hose valve on the left, which forces water through the system and out the hose valve on the right of the shutoff valve. I close all 3 circuits then run one at a time until all the air is out and the system is quiet.

Now that the system is filled with antifreeze, and since I keep getting a bunch of air in it (more than the separator can get out quickly or that I have time to wait for) I re-purge the new air by doing the same basic procedure except I only use one bucket and my outlet goes back into the same bucket that my submersible pump is pumping from. This seems to do a good job of getting the air out of the system. My supplier thinks it's introducing air. I have no idea but it SEEMS like this method is getting all the air out.

hot_rod

Are you sure the circulator is pumping down? look for an arrow on it. If so, that is a mis- applied and mi-sized check valve on the intake side.

If it is pumping up, you are pumping towards the expansion tank, not ideal.

Do a loop at a time when purging, it can take 15 minutes per loop to purge. Or more.

Glycol is tougher to get the last air out of, but not impossible.

danwheeler

I called every shop in town and finally found one an hour away that has an Amtrol EX-30 which is a 4.4 gallon. On my way! Thanks for the help guys, fingers crossed.

danwheeler

hot_rod said:

Are you sure the circulator is pumping down? look for an arrow on it. If so, that is a mis- applied and mi-sized check valve on the intake side.

If it is pumping up, you are pumping towards the expansion tank, not ideal.

Do a loop at a time when purging, it can take 15 minutes per loop to purge. Or more.

Glycol is tougher to get the last air out of, but not impossible.

definitely pumping down. What's wrong with the check valve? That part of the assembly came from the kit supplier. The only thing I did different from their typical system is turn it upside-down just because my wall is tiny and that was the best way to route everything. Picture attached.

ratio

That's a swing check. Right now it's hanging open, they rely on gravity to close them. You need a spring check if it needs to go there.

pecmsg

Did that Kit supplier also give you all the shark bit fittings?

danwheeler

pecmsg said:

Did that Kit supplier also give you all the shark bit fittings?

no, that was my choice on the sharkbite. I really prefer them especially with as much re-configuring as I'm doing to work out the issues. Maybe once I get everything working right, I'll sweat in some copper but unless someone can help me prove they are causing a problem (they definitely are NOT leaking) then I'd like to keep them at least for now. Why do you ask?

EBEBRATT-Ed

@danwheeler

I would say your whole issue is an expansion tank problem. In addition to your check valve issue

Jamie Hall

Do plan on replacing the sharkbites when you get things more or less arranged. They aren't leaking -- now. They really aren't meant for long term installation, though.

danwheeler

EBEBRATT-Ed said:

@danwheeler

I would say your whole issue is an expansion tank problem. In addition to your check valve issue

What's the issue with my check valve other than the fact that it is non-functional upside down? Is this something that could be introducing air? Or just something I should fix eventually?

I've just finished plumbing up the new 4.4 gallon Amtrol EX-30 expansion tank. I am re-purging all the lines right now.

The new expansion tank is huge. I guess I can forget about storing my beanie baby collection under the stairs

danwheeler

HomerJSmith said:

Does the pressure gauge on the right side of the air eliminator show a drop in the reading when the pump turns on?

Yes, I show a 2PSI drop when the circulator pump clicks on. Is that good or bad?

hot_rod

You should never have any sort of flow restricting valve at the suction side of a circulator. it can cause cavitation, the forming of small vapor pockets. Vaporous cavitation often presents itself as an air issue, it's not.

But the good new is with it upside down, it should be hanging open. I'm not sure why a check is need in your installation. They are used to prevent gravity flow when the pump is off. But mainly when the emitter, or tube is installed above the boiler (thermosiphon).

If it were me I would remove the large plug and that side port plug , the hinge pin is then accessible. Pull the pin, remove the flapper and reassemble the plugs. That takes one more possible cause of the turbulent, air forming condition you may be hearing, out of the equation.

hot_rod

No harm in over-sizing the expansion tank, pre-charge to 12 psi,fill to 12psi.
Your system is probably around 10 gallons of fluid.
7.93 in the tube, 1 gallon in that boiler, maybe another gallon in the piping, that small tank is adequate if properly charged.

Occasionally we hear of stuck diaphragms not allowing acceptance.

What I suspect happens when you were getting to 30 psi you opened a valve to let water out, that is where the air problem starts.

New tank, good purge, see what happens. If it is still noisy, I'd address that swing check.

Most, but not all swing checks need to be installer in a horizontal line. Swing checks are for applications with a pressure differential. When your pump is off the check has the same pressure on inlet and outlet, no "head" to shut or seal it closed.

HomerJSmith

That Grundfos pump may have a check valve on the output of the volute. That's where the check valve should be if you use one. It look like the picture and fits into the pump housing. Make sure it is installed in the proper direction. Get rid of that swing check. That pressure gauge should be a 0-30 psi gauge for better accuracy.

danwheeler

Thanks, guys. I'll eliminate that swing check once I get things working (assuming it's not causing the issue) and I'll check into that check valve on the pump itself.

I'm currently sitting in a lawn chair in front of the system eating a TV dinner watching in disbelief and amazement as the temperature continues to rise up to 108 now and the pressure has completely stalled out at 18. The new expansion tank is doing it's job now?

I still haven't cycled the system off and back on again yet. That's usually when the issues would occur. So I'm going to let it hit 120 which is where I have the boiler set, then I'll click it off with the thermostat for a bit then fire it back up and cross my fingers.

thanks,
Dan

danwheeler

Well, everything was going perfect until a few minutes ago I hit about 113F and suddenly a bunch of water swirling sounds or air came out of nowhere and made a mess out of the system. Pressure was 18PSI completely stable up to that point.

Coincidentally, my temporary thermostat just happened to flip the system off about 30 seconds after that started happening. I flipped it back on to see what it would keep doing but then the boiler started making noises so I turned that off. Now I'm running just the circulator listening to all the new air run through the system. Pressure dropped to about 8PSI if that (gage may bottom out at what looks like 8)

I think if I could throw a hydronic system off a cliff I would do it. But it's embedded in my floor.

I don't understand where air could come from with positive pressure and why not until 113 degrees while working perfectly up until that point.

When it happened, the noises seemed to start on the left side of the system around the pump and expansion tank. Then it spread to the right side of the system, I assume, once the air made it through my floor.

What the heck is going on here? I'm stumped. At least the pressure has stabilized now with the new expansion tank.

hot_rod

It sounds like the air purger, isn't. Does the top remove to see if the float in side is stuck or crud in the relief port. Those micro bubble style purgers are 90% or more efficient.
If you hear air going thru the tube on both sides, is probably is not working.

An easy thing to check, assuming the top is removable?

hot_rod

https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/21831-source/2915069-pdf

danwheeler

I think the air separator is working. It doesn't work fast but it does work eventually. I think the problem has more to do with new air being introduced. Most recently, around when it hit 113F. I'm talking about a LOT of air coming from somewhere.

After I re-purged the system, it was absolutely perfect, no air, completely quiet. Then boom, at 113F, a total disaster of air in the system. I just don't know where it came from. I don't think there's anything special about 113F, that's just where it happened. I don't think that indicates a problem with the air separator, I don't expect it to deal with a huge problem like that.

I've just finished re-purging, I've got it quiet again. I was getting some gurgles when wiggling around the new expansion tank while the pump was running. I'm not sure if that indicates air trapped in the new expansion tank or a bad sharkbite valve. If I can't figure this out, I might have to sweat all these in with copper tomorrow. Not looking forward to that but not sure what else to do.

danwheeler

hot_rod said:

It sounds like the air purger, isn't. Does the top remove to see if the float in side is stuck or crud in the relief port. Those micro bubble style purgers are 90% or more efficient.
If you hear air going thru the tube on both sides, is probably is not working.

An easy thing to check, assuming the top is removable?

I'll check it if this round of tests doesn't work though. It's a good idea. Thanks for the link. Maybe if my air separator were more effective, I wouldn't have a system meltdown when air got into the system because the separator would take it out. Not sure if that would make it a band-aid though. I believe I do hear the air making a full circle through the system so I'm not sure the separator is working 100% but I don't know what to expect of it either.

it's hard to know how much air enters the system when this occurs and how long it would take the separator to remove it.

EBEBRATT-Ed

Almost sounds like you have a restriction somewhere and pulling air into the system

mattmia2

When you heat the water the dissolved air is going to come out of solution. The air separator should remove it as it forms. There will also be some air you won't purge. Did you loosen the little cap so it can vent air? You may need go use the pump to put more fluid in as this happens. You might start out at a bit over 12 psig cold so that the expansion tank is partially filled and that fluid can take the place of the dissolved and trapped air as it is removed and if the pressure stays under 30 psig you can let it run a few days then adjust the pressure.

They sell a lot of these, doesn't mean any work right.

If it is hydronic antifreeze it is nontoxic. We would have to use rpz backflow prevention on hydronic systems if it were toxic.

danwheeler

Guys, prepare to hear the collective internet groan of 100 experienced plumbers over the age of 50.

I'm not saying this is going to solve my issue but when I wiggle this area, I get gurgling. If it's got black and white stripes and hooves...

I know, I did this to myself. That score was not right where the rubber sharkbite seal sits but it's suspect. I also found some stamped lettering on the copper. I've cut beyond the score and I'm going to clean it all up and try again. If I do get this working, the sharkbites are done for whether they hold or not.

mattmia2

That isnt your problem. Your initial problem was your expansion on tank was too small or incorrectly charged so it wasn't working and your system was going in to vacuum and pulling air in the air separator. You problem now is just the air you couldn't purge and the air dissolved in the antifreeze working their way out.

danwheeler

mattmia2 said:

That isnt your problem. Your initial problem was your expansion on tank was too small or incorrectly charged so it wasn't working and your system was going in to vacuum and pulling air in the air separator. You problem now is just the air you couldn't purge and the air dissolved in the antifreeze working their way out.

I totally hear what you're saying... Absolutely I had an expansion tank problem and that problem is now solved thanks to everyone's help in diagnosing that one.

And I think what you are saying is that it probably doesn't make sense for air to get sucked into a system at 18PSI and I agree with that.

But at the same time, it's hard to ignore what I heard when the thing last went kablam-o and a ton of air came out of nowhere. I didn't mention where this marred copper connection was... I'll post a picture of it circled.

A couple hours ago when I fired up the system and it was working great until it hit a high temp and air seemed to come out of nowhere, I first heard the air coming through the area right above the pump which is where this marred copper is. And like I say, when I wiggle that area with the circulator running, I hear air entering the system right in that spot.

I'm talking about a LOT of air when things go sideways. Not just a few dissolved bubbles or a little bit of air that was trapped somewhere. At least that's what it seems like.

not disagreeing because you could totally be right, I'm just not sure what else to do because I can't run the system once the air shows up in the quantity that it does unless I want to risk ruining my boiler.

mattmia2

Does the gauge show a vacuum? It would have to show a vacuum for air to enter there.

Cold water holds more dissolved air than hot water. The first few times you heat fresh water air is going to come out of solution. Lower pressure will also make it come out of solution so it will show up in the suction side of the circulator. It may be collecting until it gets big enough to keep the circulator from working. As soon as the water stops circulating in the electric boiler it is likely to boil at least a little before the limit can shut it down.

If no liquid is coming out then the drop to 8psi when you started at 12 psi cold has to be from air being removed(or a leak you can't see)

mattmia2

I would start at maybe 20-25 psi and see what happens. If it stops circulating again turn off the boiler and see if you can bleed some air at the top boiler drains and get it circulating again and let the air separator do its thing. Do you hear it venting air periodically?

danwheeler

mattmia2 said:

Does the gauge show a vacuum? It would have to show a vacuum for air to enter there.

Cold water holds more dissolved air than hot water. The first few times you heat fresh water air is going to come out of solution. Lower pressure will also make it come out of solution so it will show up in the suction side of the circulator. It may be collecting until it gets big enough to keep the circulator from working. As soon as the water stops circulating in the electric boiler it is likely to boil at least a little before the limit can shut it down.

If no liquid is coming out then the drop to 8psi when you started at 12 psi cold has to be from air being removed(or a leak you can't see)

ok, thanks, that makes sense. No the gauge doesn't show a vacuum in its location. Is it impossible for a vacuum to exist anywhere in the system, for example, what if there were a pinhole leak right before the pump... would we expect that to leak water or suck air? I'm actually not sure how that works.

I really don't think I have any leaks. At least, not in the concrete tubing. I pressure checked that before and after they poured with only the manifolds in the loop and it's been there for months now. My wall work *could* have a leak but I've seen zero drips.

Should I try running this thing at a lower temp like 100 for a while then slowly ramp it up over a few days or weeks to wait out the dissolved air?

I just really don't want to ruin this $1000 boiler by leaving it unattended and having this air issue show up while I'm not right in front of it to shut it down.

danwheeler

mattmia2 said:

I would start at maybe 20-25 psi and see what happens. If it stops circulating again turn off the boiler and see if you can bleed some air at the top boiler drains and get it circulating again and let the air separator do its thing. Do you hear it venting air periodically?

There are no top boiler drains unless I'm not understanding what those are. I put drains at the bottom. The highest drains on the system are the fill points or the air eliminator.

I think the air eliminator is working properly. When I have a lot of air in the system, I unscrew the black cap and I hear air escaping and the pressure gauge goes down a bit. I believe this means it's collecting air. I keep the black cap closed because early on I found that when the circulator stops, it sucks in air if the cap is open. I read about a few other people experiencing this issue. So with the way my pump is placed, pulling air from the separator, I have to be careful with that and keep the cap closed.