Expansion Tank and Fill Valve Location

rcleimbach

Hi,

I am looking for some feedback on the location of the expansion tank and fill valve in my hydronic heating system. This is a fairly new system that was installed in Oct 2023. Since then I have had the pressure relief valve replaced 2-3 times (lost count) and the expansion tank replaced once. I keep being told that they were "bad parts." Now I am starting to believe that the location of the expansion tank and fill valve is not optimal and is causing the pressure relief valve to pop. I have attached a pic showing the system and and also the bin I put under the pressure relief valve to catch any discharge. New PRV was installed in Dec 2023 and it is still popping. I placed that bin there 3 weeks ago. This is a second home and just came back yesterday after being away for 3 weeks.

Is it likely that the location of the fill valve is causing water to be added to the system unnecessarily, thus increasing the pressure of the system? Also to note, my pipes do have an anti-freeze and this is base board.

From what I have learned is that the optimal location for the expansion tank is on the suction side of the circulator and the fill valve should be located at the expansion tank where there is no pressure differential.

Thanks in advance for any feedback.

Jamie Hall

What you have read is correct. What you have isn't. But there may be additional problems -- such as, was the expansion tank set to the correct pressure to begin with?

Big Ed_4

Your problem may be your expantion is too small ...It depends on the system size , but looking at the photo you have a larger system . Looks good..... I would replace the #30 tank with an #60

rbeck53

What size boiler (BTU's) and type of radiation?

rcleimbach

@Jamie Hall The tech wrote on the expansion tank that it is set to 12 psi.

rcleimbach

@Big Ed_4 Thanks. Are there any other changes you would recommend if this was your system?

EzzyT

The circulating is pumping into the expansion tank, it’s needs to pumping away from the expansion tank which is the point of no pressure change.
I would replace the air scoop with a micro bubble air separator, move the circulator to right after the air separator and install a magnetic separator on the return side before the boiler. 

leonz

According to Mr. Holohan's writing in Classic Hydronics on pages 67, 68 and 69 you can pump/circulate return water into the boiler and have the point of no pressure change pump away from the boiler which is apparently what you have with the back flow preventer, pressure regulator and water feed valve piped to the circulator as it is now.

Based on his writing on page 69 of Classic Hydronics you need a larger expansion tank as the expansion tank you have now is too small and that is why the pressure relief valve is popping off.

Changing to a 60 size tank of 7.6 gallons may be large enough to solve this issue and save you a great deal of money and leave the air scoop and automatic vent where they are. You just have to follow the directions regarding the required amount of air pressure based on your homes size and number of floors.

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In my home I have a 15 gallon steel compression tank and an Airtrol valve connected to the Internal Air Separator that diverts air bubbles upward to the Airtrol valve in the bottom of the steel compression tank just like the steel compression tank in Mr. Holohans home it is hanging in the ceiling quietly doing its job of removing air bubbles without a care in the world.

BDR529

In short it keeps popping the relief, Right? So it is doing it's job.

Pinhole in the indirect feeding the boiler. More than 90% of the time.

The boiler gauge is always considered incompentant till proven otherwise.

Big Ed_4

The boiler feed valve is pressure sensitive .The pipe between the expansion tank and the system is the only place in the system where pressure does not change when the circulator turns on . Your feed valve is piped on the high pressure side , better than the low pressure side . Piped on the high pressure side your feed valve will not feed until the circulator shuts off .. Piped in on the low pressure side will increase the pressure above the set point ... The reason it is best to pipe the feed to the tank connection .

I think for your issue that you have had with higher pressure ...I would add more expansion , Twin in another #30 or if you have the clearance replace with a #60

SuperTech

Is the indirect tank new as well? I would shut off the water to the boiler.  If the problem continues its either the expansion tank is too small or a pinhole in the coil of the indirect. If the boiler pressure increases with the boiler temperature then it's a expansion tank issue. If the pressure increases without anything running then it's the coil in the indirect. It's a fairly simple process of elimination to figure out what the culprit is. 

The fill valve should be connected to the location of the expansion tank either way.

HomerJSmith

@rcleimbach sez,

New PRV was installed in Dec 2023 and it is still popping.

What dz that mean? At what point in the boiler cycle does that "popping" happen? I assume that it isn't a constant drip. Replacing the PRV 3 times indicates that it isn't a PRV problem unless the static pressure is so high that you are pushing the 30 psi mark on the boiler gauge. So, what does the boiler gauge say the pressure in the system is, when cold, when hot, and when the "popping" happens?
As indicated, if the gauge rises above 30 psi at the boiler's highest temp, it would indicate you might need a larger Ex tank. I would expect at that point you would get a constant dripping out of the PRV.
Things that can cause a PRV to discharge.
1) An incorrect sized Extank for the sys water volume.
2) Flashing in the boiler heat exchanger.
3) An incorrectly set or failed Pressure Reducing Boiler Feed Valve.
4) A leak from the higher pressure indirect tank into the the lower pressure boiler sys thru the indirect heat exchanger.
5) Too powerful a pump, pumping into the boiler. Is the Alpha pump set correctly?
6) A valve that isn't fully open in the sys.
Looking at the boiler gauge will give you a clue as to what is going on.
Does the boiler gauge spike (jump) over 30 psi or go over 30 psi at the boiler's high fire?

rcleimbach

@SuperTech @BDR529 The indirect is new as well. When you mention the possibility of a pinhole in the coil, you are referring to the coil inside the tank-correct? If there was a pinhole in the coil, then wouldn't the whole indirect hot water heater need to be replaced?

So the theory with a pin hole in the coil is that the water pressure in the tank is higher than the pressure in the heating loop, thus the pin hole lets water into the heating loop. This in turn drives up the pressure in the boiler causing the PRV to release? Is that correct?

HomerJSmith

Pinhole in the HX, Ya! most likely. The pinhole would have to open when the water from the boiler to the indirect HX would heat up. (Unlikely) A pinhole in the HX would push the boiler pressure up to the street pressure (60 psi), the domestic side of the tank and you would get a constant dripping from the boiler PRV.
The indirect pump should have valving on it so that you can shut of the boiler water to the tank HX. If you can do this be sure and disable the tank aquastat or sensor. If the "popping" stops, suspect the indirect tank.

HomerJSmith

Here's another thought. If you have an indirect pump and a boiler pump which is not correctly piped, you may get the two pumps operating in series boosting the boiler pressure and "popping" the PRV. I would suspect that this would happen at startup.

Mustangman

I'm not sold yet that there the expansion tank issue. Need A little more information. The fill valve piped into the bottom of the boiler is sort of a no no. Thats were all the dirt and sediment will build up which can eventually prevent system re-fill. The fill belongs right under the air scoop, connected to the 1/2" nipple. A short nipple into a 1/2" tee. Fill valve into that. Please put valves on both sides of the fill valve for ease of adjustment.
Did you check the boiler pressure when its cold? 12 to 14 psi is about right for a cold boiler. When your temp goes up to near high limit, what does your pressure gauge read? if you are near 20 psi.. you are fine. If its 30psi then we have to look at the expansion tank. First you have to take all the pressure off the system until the gauge says 0. Check the pressure in the tank with zero pressure in the system. If you are between 12 and 14 PSI, your tank pressure is good. If you read zero, chances are your tank is swampped. You can try pumping it up and see if the pressure climbs. If you get to that 12 to 14 psi, re-fill the system and watch your pressure. If you can't get the relief to quit tripping off on high pressure as the boiler runs and you see your pressure is over 30 psi, its probably the expansion tank. If you shut the boiler off and your gauge reads between 15 or 16 PSI and climbs on its own... probably the fill valve is overfilling. In fact the position of the PRV, installed on the return makes them suseptable to fouling.
An old guy once told me, sometimes the solution to a problem is simple and right in front of you. Before you start tearing things down looking for a complex problem, check the easy stuff first.
Steve

BDR529

rcleimbach said:

@SuperTech @BDR529 The indirect is new as well. When you mention the possibility of a pinhole in the coil, you are referring to the coil inside the tank-correct? If there was a pinhole in the coil, then wouldn't the whole indirect hot water heater need to be replaced?

So the theory with a pin hole in the coil is that the water pressure in the tank is higher than the pressure in the heating loop, thus the pin hole lets water into the heating loop. This in turn drives up the pressure in the boiler causing the PRV to release? Is that correct?

yES

rcleimbach

@HomerJSmith When I say "popping" I mean that the PRV is discharging fluid. It seems to be very intermittent and is not a steady drip or discharge. I did notice maybe 1-2 oz of fluid in the bin I placed under the discharge pipe leading from the PRV. This was over a 3 day period.

It was warm yesterday so the heat wasn't coming on much. I did check the gauge throughout the day and it never changed. Stayed around 12-14 psi. At one point I did turn up my living room thermostat and watched the gauge and it didn't move. Again, staying around 12-14 psi. The Alpha pump is set to auto adapt.

This morning I turned up the thermostat for my finished basement zone. After a while the pressure in the gauge was reading about 20 psi.

However, here is something that is interesting, I turned off the ball valve feeding the fill valve last night. You can see my hand on the ball valve in the upper right, After checking on it this morning I see a wet spot on the floor near the fill valve. Is that a pressure reducing valve in front of the fill valve?

Tech is coming this morning .. stay tuned.

SuperTech

That's a backflow preventer.  The fill valve is a pressure reducing valve. You could have some crud stuck in the backflow preventer that may or may not get dislodged next time the fill valve is used. If it continues to drip I'd replace it.  Signs are pointing towards inadequate room for expansion.  Expansion tank is too small or not charged correctly. 

EdTheHeaterMan

SuperTech said:

That's a backflow preventer.  The fill valve is a pressure reducing valve. You could have some crud stuck in the backflow preventer that may or may not get dislodged next time the fill valve is used. If it continues to drip I'd replace it.  Signs are pointing towards inadequate room for expansion.  Expansion tank is too small or not charged correctly. 

You may also have a over pressure in the pipe between the manual valve and the automatic feed valve which may also act as a check valve. In the way that the backflo preventer works you may have had a build up of pressure ion the section of pipe that the vent of the backflo preventer is designed to discharge as it is supposed to. Perhaps that is normal, as long as you have that manual valve closed. but that should only happen once. (until you open the manual valve again)

perhaps you could ask the service tech if they could pipe the system this way. As mentioned by @Mustangman



This is more in line with "Industry Standards" and may go a long way to resolving your issues.

Edit: Does the indirect have a separate circulator pump? If yes, you may want to see how it is connected... if the DHW pump is adding its pump head to the System pump head, that may cause the pressure addition that @HomerJSmith mentioned. This arrangement may solve that issue


Note: The Green pipe is not the actual location, just a representation of the connection location in the system.

rcleimbach

@EdTheHeaterMan Service tech just left and he came equipped with a #60 expansion tank, which he installed. He said that his company has been seeing this issue with a lot of the Buderus boilers they have installed.

He also replaced the PRV again as he said because I have antifreeze in my pipes, the releasing of fluid has a tendency to gunk up the seal in it - so best to start with a new one. He explained that the backflow preventer dripped as expected because I shut off the water supply valve and that took the pressure off of it.

We talked about a mico bubble air separator and he said that he sees them getting gunked up when there is antifreeze in the pipes.

The indirect does not have its own separate circulator.

If this problem persists, I will recommend the re-piping you highlighted in the photos.

Thanks for everyone's help!

Big Ed_4

If the pressure increases on temperature rise the problem is expansion.If pressure rises when pump is running it could be pressure reducing valve location . If the pressure stays high constant the problem is over feeding ... Process of elimination to find over feeding