Boiler Pressure Too High - Fixed Waterlogged Compression Tank but Still High

quag

I'll try to keep this short, I have a one zone hot water radiator system with 3 floors, 6 rads and a compression type expansion tank. The expansion tank was waterlogged so closed the valve to isolate it from the system and then drained it. I also removed the plug to refill it with air and drain all the water so it was empty at this point. It's one of those drainotank valves linked below. Once empty I opened the valve back up and some water flowed back in which I believe is normal.

https://www.supplyhouse.com/Bell-Gossett-113041-DT-2-Drain-O-Tank-Air-Charger-8629000-p


I then added water using a manual fill valve until the boiler pressure read 15psi, bled all the rads until I was getting out only water and no air. Turned the system back on and let it heat up but within 20 minutes or so the pressure was almost near 30psi which is what the PRV is set to so I shut it down and the pressure dropped back down to ~10psi. I also bled up on the 3rd floor but there was only air and no water anymore.

I'm confused on what's happening, one minute I have enough water and the pressure is correct. The next it's too high and I'm low on water. Is it going into the expansion tank? How do I make it stop?

Jamie Hall

10 psi may not be enough to get water to the third floor -- which would account for there being only air there (and now you'll have to purge the system again to get rid of the air...). However, the rise in pressure suggests one of two possibilities: either the compression tank isn't seeing the system pressure (are the valve or valves connecting it to the system open) or it's losing air (that valve you opened to drain it -- is it really closed tight? Is there any other air removal device like an air scoop or something on the system?)

EBEBRATT-Ed

When you say you added water did you add water to the boiler? Or to the expansion tank?


Try this. Isolate and drain the tank again. Leving the tank isolated get the boiler to the right pressure15psi should be enough, but if you bleed the top floor and have no pressure up the pressure 2 psi at a time until you have some pressure up there.

Bleed everything with the circulator off. Then open the valve to the expansion tank and feed the boiler until you have the right pressure as determined above.

If you want to get the right pressure exactly their are two ways:

1.
Measure from the top of the radiation on the third floor to the boiler vertically. You can toss a rope out a third floor window if this helps and tie a knot in it where it hits the ground pull it up and measure with a ruler. Then measure the rest of the footage to the boiler.

Once you get the total height in feet divide it by 2.31 to get the psi and add 4 psi to whatever you get.

2. get a low pressure 0-5 psi gauge and install it on the 3rd floor fill the system and bleed it. Get the gauge on the third floor to about 4 psi.

JUGHNE

Are you certain that the "A" screw for the air tube is sealing completely?

If not it could bleed air out but not necessarily water, being thicker so to speak.

Or the air tube may be plugged and you did not drain the tank completely.
The steel wire used on utility marking flags will just fit up there to clear any blockage.

quag

EBEBRATT-Ed said:

When you say you added water did you add water to the boiler? Or to the expansion tank?


Try this. Isolate and drain the tank again. Leving the tank isolated get the boiler to the right pressure15psi should be enough, but if you bleed the top floor and have no pressure up the pressure 2 psi at a time until you have some pressure up there.

Bleed everything with the circulator off. Then open the valve to the expansion tank and feed the boiler until you have the right pressure as determined above.

If you want to get the right pressure exactly their are two ways:

1.
Measure from the top of the radiation on the third floor to the boiler vertically. You can toss a rope out a third floor window if this helps and tie a knot in it where it hits the ground pull it up and measure with a ruler. Then measure the rest of the footage to the boiler.

Once you get the total height in feet divide it by 2.31 to get the psi and add 4 psi to whatever you get.

2. get a low pressure 0-5 psi gauge and install it on the 3rd floor fill the system and bleed it. Get the gauge on the third floor to about 4 psi.

I did what you said about turning the circulator off. Isolating the expansion tank and drained it. Kept it isolated, filled and bled the radiators. Then I opened the valve to the expansion tank and water went in. Added water to the system to 15psi, mine is supposed to be between 12-15. I don't get any water up top until 15 psi.

Upon bleeding the radiator I got a huge rush of air which I suspected allowed water back into the expansion tank so I isolated and bled out about 5 gallons of water. I repeated the process thinking maybe I had a lot of air in the system but I feel like I'm going in a circle now. Was all that air I just bled from the expansion tank or did I just get out a bunch more air from the system? I know the expansion tank should have some water in it but I'm not confused here. Thanks for your help, picture of my expansion tank for reference

quag

JUGHNE said:

Are you certain that the "A" screw for the air tube is sealing completely?

If not it could bleed air out but not necessarily water, being thicker so to speak.

Or the air tube may be plugged and you did not drain the tank completely.
The steel wire used on utility marking flags will just fit up there to clear any blockage.

It drained completely, it was sucking in a ton of air and blowing out water from the hose

quag

I should also mention that the pressure relief valve blows if I add too much water even though the gauge is only showing 15psi. However I have seen the gauge go past 15 psi and it will hold like when I ran it for 20 minutes and the pressure shot to to nearly 30psi.

I don't know if that means I have air still in the system or if I'm just bleeding the expansion tank charge. Also, when I'm adding water after opening the valve to the expansion tank to refill the system for the second time. Where is that water going? Into the expansion tank or up to the radiators?

EBEBRATT-Ed

The expansion tank should be "somewhere around 1/2 full of water and 1/2 full of air with the boiler cold ...give or take. You should NOT have any automatic air vents in the system.

Yes. Once the system is filled and bled with the expansion tank isolated you then open the valve to the empty expansion tank. Water will rush in until it is about 1/2 full of water.

By chance does that expansion tank have a gauge glass on the far end that I can't see?
?

quag

EBEBRATT-Ed said:

The expansion tank should be "somewhere around 1/2 full of water and 1/2 full of air with the boiler cold ...give or take. You should NOT have any automatic air vents in the system.

Yes. Once the system is filled and bled with the expansion tank isolated you then open the valve to the empty expansion tank. Water will rush in until it is about 1/2 full of water.

By chance does that expansion tank have a gauge glass on the far end that I can't see?
?

No sight glass on the expansion tank. It sounds like I still have air in the system or not enough water when I open the valve to the empty expansion tank. I don't think it gets half full and then I have to add water and bleed more air from the radiators. I would add a bunch of water but the PRV sometimes blows water if I add too much at a time without bleeding some air from the radiators so I have been doing it slowly and bleeding/filling a little at a time. I think the gauge is messed up, something like this work if installed on the side of the boiler?

https://www.homedepot.com/p/Watts-3-4-in-Plastic-Water-Pressure-Test-Gauge-DP-IWTG/100175467

Or maybe the pressure relief valve is bad? I've seen it blow at 15 psi while cold and then I've seen it almost at 30psi while hot without blowing and then I shut it down myself. I'm leaning toward the gauge

mattmia2

Where is the gauge in relation to the relief valve? It sounds like maybe the circulator is creating a large pressure differential.

Jamie Hall

"Upon bleeding the radiator I got a huge rush of air which I suspected allowed water back into the expansion tank so I isolated and bled out about 5 gallons of water. I repeated the process thinking maybe I had a lot of air in the system but I feel like I'm going in a circle now. Was all that air I just bled from the expansion tank or did I just get out a bunch more air from the system? I know the expansion tank should have some water in it but I'm not confused here. Thanks for your help, picture of my expansion tank for reference"

If you got air from the radiators on the third floor, it didn't come from the expansion tank. It came from those radiators. The only way you can "bleed air from the expansion tank" is either to drain the system completely or open the air valve on the expansion tank.

Assuming you did drain and fill the expansion tank correctly in step 1 up there, it will have air at atmospheric pressure in it when it's empty, and at whatever the system pressure is when you are running the system.

So -- get your system pressure (with the tank connected) up to 15 psi. Go and bleed a radiator. Go back and get the system pressure up to 15 psi. Rinse and repeat until you get no air out of any of the radiators.

Now this still may not be enough. You may have to actively purge the system, which is a different procedure.

leonz

Can you upload a picture of the plumbing from the boiler to the compression tank when you have time?

I have a steel compression tank and I am very familiar with how they work and they are the best way to manage air and pressure-yes I am biased.

Jamie is right, you need to bleed air from the radiators one at a time or actively purge the air from the system. Remember if you get nothing but water it's not an air problem. Push the thermostat way up and wait and then start bleeding the radiators again.

I am beginning to wonder if the valve you have in the steel compression tank is actually a boiler drain and not a drain-o-tank valve as the tank should only empty water to the point where the dip tube ends
just like a B+G Airtrol Valve.

You have come this far, and I think you need a new boiler triple gauge-preferably an American made one from Dwyer Instruments, a drain-o-tank valve and a new 30 P.S.I.G. relief valve for the boiler.

I would strongly suggest you avoid buying pressure gauges from China as I can tell you from my past experience that they are not accurate.

leonz

If you are sure you have a drain-o-tank valve in the steel compression tank you will not be able to empty it UNLESS you remove the valve completely or drain the system at the boiler drain after you close off the pressure and return pipes on the boiler to the radiators.

What is the plug you refer to and where is it??

The drain-o-tank valve It will only allow you to empty the water to the halfway point and begin
spitting air. Fill the tank to the point water comes out of the valve slowly, once that happens close the valve!!!

Now open the water fill valve for the boiler and leave it open and start bleeding the radiators again.

If all you get is water close the bleeder on the individual radiator and go to the next one and repeat the process until you reach the last radiator on the third floor.

Once all the air is gone from all of the radiators on all three floors you can open the red valve closest to the steel compression tank and let the system work to heat the home.

My only wish is for you to succeed.