Air Getting into New Radiant System After Cool Down?

[DanoWheelero]

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 HeatingHelp.com 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 as well as HeatingHelp.com. 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. Tubing is 5/8ths OB. Circuit lengths are 194, 224 and 174. "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 HeatingHelp that the air separators can **** 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

I've attached 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.

 

[Sawlog]

How many btu is that boiler?

 

[DanoWheelero]

How many btu is that boiler?

30K

 

[The Cobbler]

I would try to pull a vacuum on it & see if it holds

 

[Sawlog]

Your psi should never be at zero, even if your system is at room temp.
And the position of the tank doesn't matter. The air and water never touch each other in the tank, it has a rubber bladder inside.
How many gallon is your expansion tank? Need to be around 5 gallon tank.

 

[Sawlog]

Make sure your bladder on that tank isn't bad.
Take your pocket knife and hit the schrader valve and see if any water comes out. If so, then you bladder is bad and you have no thermal expansion. That will cause the psi to skyrocket

 

[DanoWheelero]

Update here - some guys on heatinghelp.com have been giving me some suggestions. I’ve switched out my 1 gallon expansion tank for a brand new 4.4 gallon Amtrol EX-30. I re-purged my system and fired it up. Good news is, the issue where the pressure would rise uncontrollably seems to be resolved now probably because of the bigger expansion tank. I hit 18PSI around 80 degrees and pressure completely plateaued at 18PSI.

The bad news is, just a few minutes ago, after the system had been warming up perfectly with no air noise, no issues, just a slow steady, perfect temperature rise with no pressure increase beyond 18, suddenly, a ton of air in the system. Game over.

Coincidentally, my thermostat flipped the system off about 30 seconds after that whole mess happened so I turned it back on but eventually the boiler started hissing so I turned that off and am running just the circulator pump right now. Pressure dropped to zilch or close to it. Still hearing a little air working its way around the system as its cooling down.

devastating... I was so hopeful I was going to get it. I've been at this for days now and I'm 2 hours away from home sleeping in a sleeping bag here at night. I don't know what to do with this thing. Where's this air coming from?

 

[DanoWheelero]

I would try to pull a vacuum on it & see if it holds

Should it be able to hold a vacuum? Wouldn't that just cause the relief valves to open?

 

[The Cobbler]

Im wondering if when your water cools it creates a vacuum (pressure lowers) and air gets in?

I've seen car rad hoses leak as it cools down , but not under full pressure

 

[Jeepster04]

How much pressure are you putting in the bladder tank?

If that was the first time running the system since replacing the bladder tank, maybe the system still had air in it?

 

[Sawlog]

What's your initial system psi before it heats up?
Is it holding psi when room temp?

 

[DanoWheelero]

I put 12PSI in the expansion tank.

I completely re-purged the system after adding the new expansion tank using a submersible pump, a bucket and two hoses. Got all the air out and it was perfect until it got up to operating temp them blam-o, a bunch of air from somewhere. MAYBE some trapped air made its way out of the new expansion tank? I'm not sure why it would have waited until it hit 113F to do so.

 

[DanoWheelero]

What's your initial system psi before it heats up?
Is it holding psi when room temp?

I started it at 12 PSI. Yeah, it seems to hold that at room temp just fine. I've never had any indication of a leak, drip or anything in all the pressure tests I've done. That's what's so confusing about where the air is coming from.

 

[Sawlog]

It takes awhile to get all the air out. That's why you put a air separator on these systems.
Your psi going to zero at cool down sounds like a leak somewhere. That could explain the air getting in too. Are your tubes in concrete?
Saw cut floors? ECT.
With shark bit fittings it would be easy to psi test each loop.

 

[Sawlog]

You might not have a leak until things get hot and psi goes up.

 

[Sawlog]

I would put 60 psi of air on each loop or just on all at once, but just the loops. Then you can cross that off if test is good.

 

[PoorUB]

Think about it for a minute. The whole system has 18 PSI in it. The outside air isn't pushing it's way against 18 PSI to get into the system. The only other possibility is the pump inlet pulls a negative pressure and pulls in air some where. If the pressure gauge by the air eliminator never goes to zero there is no way air is getting into the system. Your pressure gauge would have to drop to zero with the pump running to draw air into the system. You need a negative pressure to draw air in toe the system.

I don't think you are getting all the air out.
I would bump the water pressure to around 30 PSI, close one loop at a time and wire the pump so it runs constantly and see what happens. Or use your sump pump and connect it to your fill and dump valve by the 1/4 turn ball valve on the top pipe by the air eliminator. Flush each loop for an hour watching the water pressure.

I helped to floor heat in a 10,000 sqft shop and we fought air in the loops. We finally jacked the pressure up to 50 PSI, opened all the flow control valves and let it run for a week. Every morning we would come in and the pressure had dropped so we would add a bit of water. It would drop less and less every day until the last morning the pressure didn't change. Then we knew we got the air out.

 

[REDSHELBY]

Think about it for a minute. The whole system has 18 PSI in it. The outside air isn't pushing it's way against 18 PSI to get into the system. The only other possibility is the pump inlet pulls a negative pressure and pulls in air some where. If the pressure gauge by the air eliminator never goes to zero there is no way air is getting into the system. Your pressure gauge would have to drop to zero with the pump running to draw air into the system. You need a negative pressure to draw air in toe the system.

I don't think you are getting all the air out.
I would bump the water pressure to around 30 PSI, close one loop at a time and wire the pump so it runs constantly and see what happens. Or use your sump pump and connect it to your fill and dump valve by the 1/4 turn ball valve on the top pipe by the air eliminator. Flush each loop for an hour watching the water pressure.

I helped to floor heat in a 10,000 sqft shop and we fought air in the loops. We finally jacked the pressure up to 50 PSI, opened all the flow control valves and let it run for a week. Every morning we would come in and the pressure had dropped so we would add a bit of water. It would drop less and less every day until the last morning the pressure didn't change. Then we knew we got the ai

 

[REDSHELBY]

Bleed each loop separatly keeping shut offs closed after bleeding. Bring loops online one at a time. Let each loop run for awhile before bringing another loop online.

 

[Jackfre]

The suggestion to purge with your domestic system with the higher pressure should be followed. Run the water thru it for a bit in each individual zone. The higher velocity/pressure will pick up or move more the air to the separator. continuing with your sump pumps will keep you sleeping on the floor Those Amtrols ****, quite literally. Replace with a Spirovent. You want to learn so I would suggest Dan Holahan’s “Pumping Away” & “Primary Secondary Piping.” Is the expansion tank on the suction side of the circulator?

 

[Firebrick43]

The suggestion to purge with your domestic system with the higher pressure should be followed. Run the water thru it for a bit in each individual zone. The higher velocity/pressure will pick up or move more the air to the separator. continuing with your sump pumps will keep you sleeping on the floor Those Amtrols ****, quite literally. Replace with a Spirovent. You want to learn so I would suggest Dan Holahan’s “Pumping Away” & “Primary Secondary Piping.” Is the expansion tank on the suction side of the circulator?

He is using antifreeze, not water


To the OP, your using a sump pump to fill? They are a low pressure pump, not suitable for this.

 

[DanoWheelero]

He is using antifreeze, not water


To the OP, your using a sump pump to fill? They are a low pressure pump, not suitable for this.

Yeah but I think I was using the wrong term... not a sump pump but a submersible pump, the one I use to drain my hot tub. It'll make about 12 PSI which seems to be enough to get me started.

I can see why you'd want to do an initial flush with domestic water supply but in my case, my well water is full of sediment and I have it winterized so I'm trying to avoid firing that back up. I also don't have my building plumbed which means dragging hoses across the yard in a foot of snow and 20 degree temps.

As of right now, I left the system running overnight with the boiler set to 100 degrees with the new 4.4 gallon expansion tank and the black cap on the air separator open and things seem OK. I was able to cycle the system on and off without introducing any new air which is a huge improvement. Pressure is holding around 19PSI and I've just set the temp up to 120 which is also doing OK.

The only issue I've got right now is that the boiler is making some very subtle but consistent noise like a coffee maker. It's not a lot but doesn't seem right. Maybe it's just the last of the tiny air bubbles hitting the element.

It seems like the root of my problem was the expansion tank being too small. That was requiring me to release excess pressure to avoid tripping the 30PSI blow-off valve and then when the system cycled off, it would cool and the pressure would go negative and **** in air from somewhere.

so at this point, it's stable or at least vastly improved - just monitoring it to make sure the boiler noise doesn't get too bad.

 

[PoorUB]

Yeah but I think I was using the wrong term... not a sump pump but a submersible pump, the one I use to drain my hot tub. It'll make about 12 PSI which seems to be enough to get me started.

It will work, but higher pressure will push the air out faster. We always used a pump that would produce 40 PSI and run it for a few minutes per loop. It would get out the great majority of the air.

On larger jobs we had a 1-1/2 hp pump that would do 60 PSI and 1" hoses right to the manifold.

Like I mentioned earlier, you could wire up your pump and just let it run and keep an eye on it. It should get the air eventually.

 

[Firebrick43]

Yeah but I think I was using the wrong term... not a sump pump but a submersible pump, the one I use to drain my hot tub. It'll make about 12 PSI which seems to be enough to get me started.

I can see why you'd want to do an initial flush with domestic water supply but in my case, my well water is full of sediment and I have it winterized so I'm trying to avoid firing that back up. I also don't have my building plumbed which means dragging hoses across the yard in a foot of snow and 20 degree temps.

As of right now, I left the system running overnight with the boiler set to 100 degrees with the new 4.4 gallon expansion tank and the black cap on the air separator open and things seem OK. I was able to cycle the system on and off without introducing any new air which is a huge improvement. Pressure is holding around 19PSI and I've just set the temp up to 120 which is also doing OK.

The only issue I've got right now is that the boiler is making some very subtle but consistent noise like a coffee maker. It's not a lot but doesn't seem right. Maybe it's just the last of the tiny air bubbles hitting the element.

It seems like the root of my problem was the expansion tank being too small. That was requiring me to release excess pressure to avoid tripping the 30PSI blow-off valve and then when the system cycled off, it would cool and the pressure would go negative and **** in air from somewhere.

so at this point, it's stable or at least vastly improved - just monitoring it to make sure the boiler noise doesn't get too bad.

That is a pretty big pump, most cant make 20 feet of head, let alone the 27 to equal 12 psi. 12 isn't enough in my opinion.

What brand/model of air separator is that? Is it a microbubbler? And does it have an automatic vent? If so I have seen some that will **** in air when cooling due to a faulty valve. I screw the cap on my spirovent when I shut it down to keep it from drawing in air although its just a little over all spring/summer/fall, but screwing it down tight doesn't allow in any air.

 

[fitter30]

System doesn't need any more pressure than 10 - 12 lbs. Expansion tank air pressure on cool system 2lbs less to same than water pressure. When pressure testing valve off the makeup. Take few pics of boiler and piping (don't get to close). New expansion tank should have 12 lbs of pressure from the manufacturer. Changing pressure in tank use a hand pump not a compressor unless your very carefull.

 

[65ranchero]

I had a similar problem where the loops would not heat sections of the floor.
all loops were purged many times and still had a problem.
I think I suggested to the plumbers to disconnect all the lines and blow air through them I turned out that (I think ) 2 or 3 out of the 4 loops the plumbers hooked the returns to the inlet manifold.
It turned out the the plumber had his head in another place.
He got very confused about inlets and returns.

Just a thought!