Hydronic Gas Boiler high pressure issue

unbelievable21

I have a pennco boiler installed in 2001 in a house i just bought. Recently I replaced a few parts with new: circ pump, water feeder with backflow, 2 new zone valves and zone board, new drain at boiler inlet, new expansion tank and pressure relief valve, new auto can vent. All these new parts and I now have a high pressure issue. Ill try to explain:

Boiler is filled to 12 psi. Thermostats kick on and boiler temp rises to 180F and pressure to 20psi (normal). Thermostats shut off. Temp decreases slowly back to 120F and pressure remains at 20psi. Should drop back down to ~12. Let's say if i turn thermostats back on at this point - temp rises to 180F and psi rises a little more to 22psi. Shut off thermostats and temp decreases as usual and pressure stays at 22psi. This continues every time I turn on the thermostats - pressure keeps increasing slightly until 30psi in which pressure relief valve starts to leak out water. In other words - pressure never retreats. (Keep in mind Feeder is set at 12psi out of the box. Could it be faulty? Could it have been damaged when pressed or soldered that would make it do this?).


I tried a test in which i shut off the water to the boiler before the feeder and released some water to drop pressure back to 12 psi. I turned on both thermostats and again temp rises to 180F and pressure to 20psi. Turned off thermostats and pressure still remained at 20psi the first time. I decided this may have been due to the small amount of water between shutoff valve and feeder which held water and was most likely let in during or after this first run. So I relieved some more water again from the boiler with shutoff valve still closed and dropped the pressure back to 12psi. I turned on both thermostats again. Temp rose to 180F and pressure to 20psi. I shut off thermostats and the pressure dropped to about 10psi. I did not do anything again. About 8 hours later when I came back to it, the pressure showed closer to 5 psi.

1 other thing id like to mention is for example when the boiler installed gauge reads 20psi and shutoff water valve is open - i hook up a water gauge to drain valve and I get 12 psi on that gauge. When the boiler installed gauge reads 20psi and the shutoff valve is closed and I hook up this water gauge to the drain valves - I get 0psi on this gauge on these drain valves.


Thats the extent of my testing with this issue and I was hoping someone could give their opinion on possibilities for why this is happening etc. My opinion is it is a faulty new feeder or installation of it. But would be helpful to get some opinions before buying and installing another 1 if for some reason that it is not the case. Because my only thinking is if I am getting 2 different pressure readings in 2 different spots then maybe the feeder is working fine but is detecting a different pressure in that area . if that even makes sense. Anyways, Any help would be appreciated this has been exhausting. I can provide any more information if needed, thanks.

ScottSecor

Was expansion tank set to 12psi (same as the feeder)? I'm guessing we get about one in fifteen expansion tanks that are no where near 12psi right out of the box. I would say about one in a few hundred pressure reducing valves are not set correctly or faulty.

unbelievable21

ScottSecor said:

Was expansion tank set to 12psi (same as the feeder)? I'm guessing we get about one in fifteen expansion tanks that are no where near 12psi right out of the box. I would say about one in a few hundred pressure reducing valves are not set correctly or faulty.

Thanks for the response. I checked the new tank and did the tap test on it, doesnt sound like any water is in it. Checked pressure again now with tire gauge and 3 readings between 11-13psi (precharge is 12).

Jamie Hall

The tap test is unreliable with bladder tanks. The only reliable way to check the tank is to isolate it from the system and get all the water out of it and then adjust the air pressure to what the feed valve is set for -- 12 psi. Then hook it back up to the system, Some installations have convenient valves to do that. Most don't.

unbelievable21

Jamie Hall said:

The tap test is unreliable with bladder tanks. The only reliable way to check the tank is to isolate it from the system and get all the water out of it and then adjust the air pressure to what the feed valve is set for -- 12 psi. Then hook it back up to the system, Some installations have convenient valves to do that. Most don't.

Ok. i do not have those convenient valves to do that so easily. based on my steps I did would that be your first guess for the issue im having? The tank and feeder are both new.

hot_rod

Set the pressure to 12 psi cold, then valve off the fill valve. Does pressure rise to 30 psi?
is so the tank is waterlogged or diaphragm stuck against the nipple

unbelievable21

hot_rod said:

Set the pressure to 12 psi cold, then valve off the fill valve. Does pressure rise to 30 psi?
is so the tank is waterlogged or diaphragm stuck against the nipple

when valved off it rises from 12 to 20psi when heat is turned on the first time. when done heating the temperature drops and the pressure remains at 20psi. i drain a little water from relief valve at this point and boiler gauge gets back to 12. next time i turn on heat temp rise and pressure rises again like normal. at this point when i turn off heat both the temperature and pressure go down as they should. (the reason i think it pressure remains at 20psi after valve is closed the first time heat is turned on is because in my estimation the filler , even though it is set at 12psi, allows more water in between the shutoff valve but before the filler...would that make sense that filler is faulty?)

neilc

where is the tank and make up feed in relation to your circulator?
can you post a picture showing all that?

unbelievable21

neilc said:

where is the tank and make up feed in relation to your circulator?
can you post a picture showing all that?

circ is at the inlet to the boiler. tank is right after the outlet from the boiler. feed is off the main water supply after the shut off valve to boiler and after the backflow w/ vent. the piping right after this feeder joins with the returns as it meets the circ at inlet of boiler. attached some pics

hot_rod

Temperature effects pressure also. When you read 12 psi what is the boiler temperature?
what is the temperature when it reads 20?

when the boilers shuts off  pressure at 20, you would need to wait until it drops to the same temperature it was when it started at 12

water expands and pressure goes up, pressure drops as it cools down, basically 

Read all pressures with the power off so circulators are not running

Looks like a new press ball valve the fill. Very remote chance it is not shutting off 100%

if it never goes above 20 psi it will work fine. That is not excessive.  If it keeps creeping above that, water is being added.

EBEBRATT-Ed

Unless I am mistaken you have the expansion tank connected to the discharge side of the circulator and the feeder connected to the suction side. The have to be connected to the same side. I would disconnect the feeder and tie it into the expansion tank pipe.

Your gauge may be off. Install a temp pressure gauge on one of your boiler drain valves with a garden hose connector.

Remove your expansion tank and check the pressure of the air side while it is off the boiler

Lyle {pheloa} Carter

EBEBRATT-ED is on the right track. It looks to me that the boiler feed is on the return from the system and the expansion tank is on the supply to the system. So when the circulator pump kicks on it feel the resistance of the water being pulled back from the system and part of the force of the water being pushed into the system is being canceled out by the expansion tank.. Normally we like to connect the water supply at the point of no pressure change, which is the expansion tank.
I realize you didn't have a problem before you changed these components, I have seen this problem dealt with by lowering the boiler feed pressure to about 5-7 lb. When the circulator pump kicks on and goes through a few Cycles the pressure increases to the normal pressure. This wouldn't be the best solution because it lessens the efficiency of the pump and the air separator doesn't work as well. However it may be a solution until the system can be replied.

hot_rod

EBEBRATT-Ed said:

Unless I am mistaken you have the expansion tank connected to the discharge side of the circulator and the feeder connected to the suction side. The have to be connected to the same side. I would disconnect the feeder and tie it into the expansion tank pipe. Your gauge may be off. Install a temp pressure gauge on one of your boiler drain valves with a garden hose connector. Remove your expansion tank and check the pressure of the air side while it is off the boiler

Good catch.

 Sure be nice to get the tank and fill on that boiler return pipe. Plenty of room in the piping above the circulator. A 1 hour job with a press tool and a few fittings 🥴
Air purger, my least favorite type, is in a good location.

The tank does not need to be at or below the air purger .

unbelievable21

EBEBRATT-Ed said:

Unless I am mistaken you have the expansion tank connected to the discharge side of the circulator and the feeder connected to the suction side. The have to be connected to the same side. I would disconnect the feeder and tie it into the expansion tank pipe.

Your gauge may be off. Install a temp pressure gauge on one of your boiler drain valves with a garden hose connector.

Remove your expansion tank and check the pressure of the air side while it is off the boiler

the feeder is there to regulate the pressure coming from the main (at around 45 psi) to ~12psi. If i move it to where you say then wouldn't water enter the boiler unregulated at 45psi?

gauge being off is a possibility. I have tested at the drains and received different pressure then what is indicated on tridicator. For example, when it says 20psi on boiler, i am seeing 12psi at drain by the circ.

unbelievable21

Lyle {pheloa} Carter said:

EBEBRATT-ED is on the right track. It looks to me that the boiler feed is on the return from the system and the expansion tank is on the supply to the system. So when the circulator pump kicks on it feel the resistance of the water being pulled back from the system and part of the force of the water being pushed into the system is being canceled out by the expansion tank.. Normally we like to connect the water supply at the point of no pressure change, which is the expansion tank.
I realize you didn't have a problem before you changed these components, I have seen this problem dealt with by lowering the boiler feed pressure to about 5-7 lb. When the circulator pump kicks on and goes through a few Cycles the pressure increases to the normal pressure. This wouldn't be the best solution because it lessens the efficiency of the pump and the air separator doesn't work as well. However it may be a solution until the system can be replied.

water discharges from the boiler from that pipe in the first pic. it loops around and up into the air scoop/expansion tank. it is on the supply FROM the boiler. the circ is located on the supply before the boiler, as well as the feeder before joining together with the returns

unbelievable21

hot_rod said:

Temperature effects pressure also. When you read 12 psi what is the boiler temperature?
what is the temperature when it reads 20?

when the boilers shuts off  pressure at 20, you would need to wait until it drops to the same temperature it was when it started at 12

water expands and pressure goes up, pressure drops as it cools down, basically 

Read all pressures with the power off so circulators are not running

Looks like a new press ball valve the fill. Very remote chance it is not shutting off 100%

if it never goes above 20 psi it will work fine. That is not excessive.  If it keeps creeping above that, water is being added.

it has gone above 20psi. that is the issue. pressure never goes down on gauge. temperature does. pressure stays at 20psi and when i run boiler again it goes to ~22psi. then i shut off and it stays there but temp drops. next time i run boiler pressure goes to ~24psi. i shut off and it stays at 24psi and temp decreases as usual. process continues until 30psi is reached and PRV starts to leak.

neilc

EBEBRATT-Ed said:

Unless I am mistaken you have the expansion tank connected to the discharge side of the circulator and the feeder connected to the suction side. The have to be connected to the same side. I would disconnect the feeder and tie it into the expansion tank pipe.

Your gauge may be off. Install a temp pressure gauge on one of your boiler drain valves with a garden hose connector.

Remove your expansion tank and check the pressure of the air side while it is off the boiler

Ed and Lyle nail it,
this is pumping away x's 2, 1.01, fail,
connect the feed to the tank,
right now you're sucking from the feed as you pump to where the pressure does not change(at the tank),
I bet(know) if you disable the boiler, and just run the circ,
you would see the same increase, from cold fill 12, up to the 20 you're landing at,
move the feed to the tank connection,
and pump away,
there's a book in the store here that explains this,
or most boiler piping diagrams show same.

MikeAmann

Um, @unbelievable21 is not crazy, and he has explained the problem correctly.
I just replaced my mother's boiler expansion tank last night and the system is doing exactly as he describes. Same with my house. It doesn't matter the orientation of the tank either. And both systems have the circ pumping INTO the boiler (feed there also) and the air scoop, air bleeder, and exp tank connect to the supply side of the boiler. Only one zone. This is the way it was done 50+ years ago. And it has worked all of those years. The gauge on the boiler reads between 5 psi cold to 20+ psi hot. And if I "feel" the tank, it seems like there is no water flowing in or out. No temperature change either. Why? Is not having the tank at PONPC the reason for this?




My neighbor across the street just bought an expansion tank and air bleeder today to replace his. His system was installed only 20 years ago (house had electric heat). I will investigate how his system is plumbed.

neilc

the system pressure at the tank doesn't change*,
when the circ pumps towards the tank, the inlet of the circ is a lower pressure than at that the tank,
if your feed is before the circ, the feed sees that lower pressure, and compensates raising the pressure into the circ, to the preset 12~15,
now on the outlet of the circ, (incorrectly pushing into the tank), that pressure rises, taking up some of the tank air cushion, and you raise the entire system pressure all the way thru the system, until the feed into the circ is back up to the preset 12~15, note that you're now seeing 20~25, or whatever, on the circ discharge side,
and have now raised the entire static system pressure (the pressure when the circ is off) to the 20 you're seeing,
* doesn't change unless the circ pulls on the inlet and feed as described above,

try this, system/circ off,
lower the system pressure to a cold 12~15,
shut off the manual feed valve to the system fill,
now start the circ, let it run,
shut the circ back off and the system will be back to the 12~15 you started at,

MikeAmann

neilc said:

the system pressure at the tank doesn't change*,
when the circ pumps towards the tank, the inlet of the circ is a lower pressure than at that the tank,
if your feed is before the circ, the feed sees that lower pressure, and compensates raising the pressure into the circ, to the preset 12~15,
now on the outlet of the circ, (incorrectly pushing into the tank), that pressure rises, taking up some of the tank air cushion, and you raise the entire system pressure all the way thru the system, until the feed into the circ is back up to the preset 12~15, note that you're now seeing 20~25, or whatever, on the circ discharge side,
and have now raised the entire static system pressure (the pressure when the circ is off) to the 20 you're seeing,
* doesn't change unless the circ pulls on the inlet and feed as described above,

try this, system/circ off,
lower the system pressure to a cold 12~15,
shut off the manual feed valve to the system fill,
now start the circ, let it run,
shut the circ back off and the system will be back to the 12~15 you started at,

That's a great explanation @neilc , and I completely follow what you said.
I will do that test tonight. BTW, once the system pressure is set, I leave the auto feed off.
The million dollar question is, without reconfiguring the entire system to pumping away, is there a location that I can put the expansion tank where it can do the job that it is supposed to do?

pedmec

location of point of no pressure change is exactly the problem in relation to the circulator. Circulator moves water by creating a pressure differential in the system. Where the pressure differential happens depends on the the location of the expansion tank. If you pump into the expansion tank the differential happens mostly on the suction side of the circulator. So the pressure that you are seeing depends on where the gauge is located. Picture if you can.

System fill pressure is 12 psi @ 60 degrees (cold start)
System calls for heat.
Circulator comes on and (depending on size of circulator) creates the pressure differential.
But because its pumping into boiler with expansion tank on discharge it needs to happen on the suction side. Now say for **** and giggles the circulator creates a 6 psi differential. Most of it has to happen on the suction side.
System pressure at suction drops to 6 psi. fill valve, feeling only 6 psi starts to add water to system until it reaches 12 psi. the boiler water, which was at cold start starts to heat up and expands.
thermostat satisfies. circulator stops and the new psi is 20.

Because you have zone valves you also have multiple system curves so that differential is going to change with whatever zone is on.

neilc

MikeAmann said:

neilc said:

the system pressure at the tank doesn't change*,
when the circ pumps towards the tank, the inlet of the circ is a lower pressure than at that the tank,
if your feed is before the circ, the feed sees that lower pressure, and compensates raising the pressure into the circ, to the preset 12~15,
now on the outlet of the circ, (incorrectly pushing into the tank), that pressure rises, taking up some of the tank air cushion, and you raise the entire system pressure all the way thru the system, until the feed into the circ is back up to the preset 12~15, note that you're now seeing 20~25, or whatever, on the circ discharge side,
and have now raised the entire static system pressure (the pressure when the circ is off) to the 20 you're seeing,
* doesn't change unless the circ pulls on the inlet and feed as described above,

try this, system/circ off,
lower the system pressure to a cold 12~15,
shut off the manual feed valve to the system fill,
now start the circ, let it run,
shut the circ back off and the system will be back to the 12~15 you started at,

That's a great explanation @neilc , and I completely follow what you said.
I will do that test tonight. BTW, once the system pressure is set, I leave the auto feed off.
The million dollar question is, without reconfiguring the entire system to pumping away, is there a location that I can put the expansion tank where it can do the job that it is supposed to do?

I leave my fill valves closed, but I check the boiler pressures periodically, next day, then 2 days, 5 days, a week, 2 weeks at the most,

I think it's easier to move the feed connection over to the tank, but,
you could move your tank to be on the same line as the feed also,
your call.

MikeAmann

@pedmec , I follow that.
NO zones - just one loop for the whole house.
Now consider this:
System fill pressure is 12 psi @ 60 degrees (cold start). Fill turned OFF.
Turn boiler on, no CFH, no circ running, boiler just wants to heat the water to the LO limit (140).
Gauge on boiler - pressure rises (20), and rises (25), and rises (almost 30).
The FLO-CHEK is after the exp tank.
Isn't the expansion tank supposed to give that heated expanding water a place to expand to?
It's like the tank isn't even there.

pedmec

In the situation you are describing, absolutely. In that case i would check the precharge on the tank, but also make sure that the temperature of the water does not continue to increase as the cast iron will, even thou there is not flame, continue to increase the water temperature in the boiler. The cast iron has good thermal mass and with no water flowing will continue transferring heat from the cast iron to the boiler water.

neilc

well now, wait,
you ran the boiler without the circ? and the pressure went up to 20, and did not come back down ?
with out the circ you would not have heated all the system water, so the expansion wasn't even complete,

"It's like the tank isn't even there."

have you checked the air pressure under the tank?
and that there's no water there? ie:failed tank?
can you isolate the tank from the rest of the system(water pressure)?

MikeAmann

I just reread the thread I made about this same issue regarding the expansion tank I installed for my IWH.
https://forum.heatinghelp.com/discussion/185619/expansion-tank-not-taking-the-extra-pressure/p1

I had a thought - we all are probably assuming that on a new pre-charged tank (12 psi) that the diaphragm is sitting up against the nipple. Common sense, right? But what if it isn't? Suppose that the diaphragm is actually sitting in the middle of the tank. Now the tank gets installed, whether upside-down or right-side-up, we now have a full tank of air with a piece of rubber in the center. Air is compressible, water is not. Now we fill the system and set it to 12 psi. I would think that the air on the water side would (eventually) come out into the water and escape via the air vent. But is it possible that we have just trapped a big air bubble in the tank that can't be removed? Maybe I should pull the tank down, verify the 12 psi pre-charge, and then fill it with water before re-installing?

But my plan is to relocate the tank to a more appropriate PONPC location and install a pressure gauge at the air scoop where the tank was located.
So without reconfiguring the entire system, I would want to move the tank to the suction side of the circulator, correct?

neilc

MikeAmann said:

But my plan is to relocate the tank to a more appropriate PONPC location and install a pressure gauge at the air scoop where the tank was located.
So without reconfiguring the entire system, I would want to move the tank to the suction side of the circulator, correct?

yup,
and it's the tank that is the PONPC, which you want to pump away from,
PONPC is not a "other" location in the system, it's the tank where it connects,
the tank connection wants to be on the suction side of the circ.

pedmec

in my opinion it would be just as easy to move the circulator after the expansion tank or mve the expansion tank close to the suction side of the circulator.

on the supply side there is a straight piece copper to cut the circulator in.

MikeAmann

@pedmec
Supply side - no copper - black iron all the way to the FLO-CHEK. Hard to move the circ.
Besides, I just redid that piping and although not pumping away from the boiler (supply side), I like the location - easily serviceable.

I am going to move the expansion tank to the return copper piping. Much easier.
It won't exactly be close to the circ, but at least it will be on the suction side.

MikeAmann

@pedmec , @neilc
So this got the better of me and I attacked it last night.
But where to relocate the expansion tank? Right here in the return pipe.

Someone made a thread last week asking about installing an air bleeder in the return line. I had previously done that. The answer was that it was not a good idea because it could actually let air into the system. I made a few measurements and that tee was in the perfect location for the tank. Good thing that I sweat using acetylene. The water still sitting in that pipe made this a longer than desired process. I had to use the air compressor to blow into the tee. Bonus, the sediment is now out of the heating loop. It looked like salt or sugar.

I added this wye years ago (to the supply pipe) as a way to drain the baseboard loop. Or as a way to let air in so that the boiler could completely drain. I attached one of those screw-on garden hose gauges to the drain valve, but I substituted a lower pressure gauge. It seems that it reads low by 5 psi.


Now we get to the good stuff. I removed the exp tank from the air scoop location and plugged that hole.

I checked the pressure with the tank disconnected - my gauge read 11 psi. And the diaphragm was up against the nipple. I let all of the air out of the tank. And it was very easy to unseat the diaphragm just by blowing in the nipple by mouth. So not stuck. I blew in again to move the diaphragm - and it did move. I wanted to get the diaphragm near the middle of the tank before installation, so while blowing, I held the schrader valve open. When I let the schrader close, the diaphragm was somewhere near the middle of the tank, and there now had to be a vacuum on the air end. Then I filled the nipple end with water. It took about 7 quarts.



Notice the gray strap securing the tank. We'll get back to that later.
With everything plugged and sealed, I filled the system while bleeding the air out.
Let me repeat, the tank has 7 quarts of water on the nipple side and a vacuum (not 12psi) on the air side. I don't know what the tank weighed empty, but with the water it weighed 16.5 pounds. I had planned to just get the water back into the pipes, relieve any pressure in the pipes, and then charge the tank to 12 psi plus some amount to account for the weight of the water. I used my tire pressure gauge to measure the air side and it read 4 psi. HUH? There WAS a vacuum there, now pressure. Ok, let's run with it.

I added water to set the system pressure at 12 psi (65* F). The other gauge read 7 psi (that gauge reads 5 psi low). I fired the boiler and the circulator came on when the aquastat allowed it to, and it ran all the way up to the HI limit of 170*. The system pressure was now at 20 psi.




This is important - I felt the top of the tank, and it was hot. And I could tell just where the water line was, which was at the "shoulder" near the top. Normally I would remove a little water to lower the system pressure, but instead I bled some air out of the tank, which let more water into the tank. I lowered it to 16 psi (9.5 on the other gauge) and went to bed. In the afternoon, I read 12 psi (at 150*) on the boiler gauge. Again I felt the tank for the water line and decided that I would like that level to be somewhere close to the gray strap. So I added a little more water (3 psi increase) and bled air to get back to 12 psi. I will continue this until I get the water level where I want it. More importantly, (with the tank now actually being able to do its job) the system pressure seems to only vary by 5 psi.
PUMPING AWAY WORKS! Move your expansion tanks to the suction side of the circulator.


I forgot to mention, I leave the autofill OFF once filled. The results above were in no way affected by any extra water being added by autofill.

neilc

Nope,
wrong, or I'm reading this wrong.

when you had the tank disconnected, and were blowing on it,
YOU SHOULD HAVE PRECHARGED THE AIR IN THE TANK TO what you want for system pressure, 12~15,
that was your opportunity,
now it's a do over.

precharge air in the tank first, with no water pressure on it,
then you add water to the system,

I don't see where the Y, or tank is connected now,
wanna post another distant picture showing tank, and circ, and the piping between, all in one

Jamie Hall

A couple of things about expansion tanks which are relevant. First, there are two kinds -- bladder tanks and diaphragm tanks. In bladder tanks, when there is no water in them, the bladder will unfold and be lying on or near the water connection. In that condition, the air pressure on the AIR side should be the same as (not more than) the cold system pressure. The same is true of diaphragm tanks, except that there will be some air trapped on the water side -- but not much. In that condition, when the system is cold, there is a maximum of air volume in the tank. As the system warms up and the water expands, it expands into the water side, and this moves the bladder up, compressing the air. Since there is a large volume of air, and the volume of water doesn't change all that much, the pressure won't change much either.

Also the question was asked shouldn't the tank get warm as the water flows in? Well, a little -- but note what I said above about the volume of water. It isn't much, and so the temperature change in the tank will be minimal.

Edit -- one other thing I might add: some people have the idea that you can tap on the side of an expansion tank and get some idea as to how much water is in it. This works, sort of, with a diaphragm tank. Doesn't work with a bladder tank, as the bladder -- not the water -- is what is in contact with the wall.

MikeAmann

@neilc
I hear what you are saying, and yes this goes against the preferred way of connecting an expansion tank, but what can I say, IT WORKED.
I would bet that if I did remove the tank and check the pressure, it would read 12 psi.

@Jamie Hall
Thanks for the summary of the tanks. I was completely surprised that I could tell exactly where the water line was.

Can someone figure the volume increase due to expansion?
Mom's system holds between 15 and 20 gallons and I am raising the temperature from 70 to 170 degrees. The expansion tank can hold 4.4 gallons. Thanks.

MikeAmann

Another forgotten detail:
At one point while the system pressure read 12 psi, I very slowly added water and I heard a creaking noise. All I had to do was reach up and put my hand on the tank to feel the diaphragm moving. That's when I knew that the tank was actually working.

hot_rod

It be highly unusual to get a bag or bladder tank like that from Home Depot, You have a diaphragm tank. The other indication is the crimp around the tank, a hoop inside holds the diaphram in place in that crimp groove

A very simple correction would be a press tee into the horizontal tube at the circ. Remove the circ mounting bolts to allow you to press a tee into that location, move the tank and fill valve there and now you are pumping away

Charge the tank to what you intend to fill to.

The Amtrol Handbook available at their site has the math and charts to figure out expansion volume 

Ae have done several coffee with Caleffi webinars in expansion tank sizing. Go to the Caleffi North America you tube playlist

MikeAmann

@hot_rod
Would you label the supply and return in your pic?

pedmec

Just a crazy question. you have multiple air separators in your system? The new pictures don't look anything from what was previously posted.

MikeAmann

@pedmec
I knew this simple thing would get complicated.
I straightened out some of the pipes to make things much simpler. I didn't actually change anything - I just made the CW supply piping to the boiler and HWH a straighter route. It's all in the pics above.
I will describe:
Off of the back of the boiler (HOT, supply) runs up to the air scoop & Hy-vent. The exp tank WAS connected to the now plugged port at the bottom. Next in line is the FLO-CHEK.
Then the pipe runs over the steel beam and that is where the wye is for draining the baseboards.
That is where the 30 psi gauge is.
No zones - whole house, one loop.

Returning from the baseboards is the tee where the exp tank now is. I did have a HY-vent installed there. That is gone and I rotated the tee down to connect the exp tank. That return pipe then jumps over the steel beam and heads back to the circulator which pushes INTO the boiler. But before the circ, there is a drain valve for purging the air (hose in a bucket) and a valve that I close so that the cold water from the autofill pushes through the circ. That connection is at the lowest point at the boiler drain valve.

That's it - the complete loop.

The change that I made last night was moving the exp tank from the supply side to the return (or suction) side of the circ. That's it.

hot_rod

MikeAmann said:

@hot_rod Would you label the supply and return in your pic?

The return is the piping in the lower portion of this pic, So any piping connected to, and above that red circ

So that horizontal pipe, lowest in the pic is where a tee could be installed for the tank and fill.

Thus turns the system into a “pumping away” configuration 

You have  plenty of expansion tank capacity

MikeAmann

@hot_rod
Thanks. Your pic confused me because the exp tank is on the supply side, just like mine was.
I was saying to myself how the heck is this pumping away?

hot_rod

The tank needs to be at or near the inlet if the circ. If the circ was on the supply after the air purger, then the tank would be fine under the purger

Im assuming your circ is pumping into the boiler? Should be an arrow in the body.

Wherever the tank get mounted, so should the fill valve

I think my proposed location would require the least amount of modification