Boiler psi

fuse_5

Hello, 
I have a hot water boiler in my house. It is a Lennox 80% installed in 2003 natural gas fired. I was looking at the temp and psi gauge today and noticed the psi was low. It was 0 when the boiler is not on, then it went up to approx 5 psi when it kicked on. Temp usually runs at 180-200. My regulator says its preset to 15 psi with a low limit of 10 psi. Everything seems to work fine but I recall seeing the psi gauge at around 15 psi in thr past. Should I be worried? Thanks 

JUGHNE

With the boiler at 190 degrees (hot-damn hot), slowly add water to get up to 12-15 PSI.

fuse_5

Yeah Ive seen the temp go past 200. The regulator full valve was just replaced last winter - shouldn't it auto regulate the pressure? 

JUGHNE

Is the water supply valve before it open?

It is adjustable usually.

And you can possibly turn the temp of the boiler down.

HomerJSmith

Pics of your expansion tank and fill valve would be helpful. These gauges aren't alway accurate. Verify the pressure with another bibb gauge plugged into the boiler drain. Bibb gauges are usually high psi gauges and I replace the gauge with a 30 to 50 psi gauge for better accuracy.

EBEBRATT-Ed

Could be the expansion tank, could be a bad gauge, could be a bad PRV.

Troubleshoot one at a time. Install a temp gauge in the boiler drain as @HomerJSmith mentioned that will tell you about the gauge.

If the boiler gauge is ok. Add water to the system so you have 12-15 psi when the boiler is cold or warm (not ripping hot). The pressure should rise some what when the boiler is hot (maybe 20-24psi) if it goes over that the expansion tank may be bad.

You can adjust the PRV. If it is old they can get gunked up with sludge and may fail to work right. They can be rebuilt but most would replace considering the cost.

fuse_5

Ok I just checked the pressure fill valve and moved the tab on top of it.  As I was flipping it upwards (for just a second), it started to sound like water running through the pipe. I then returned it to its original down position immediately (as pictured) and the water rushing sounded for an additional 20 seconds or so then it gradually stopped. The pressure on the boiler gauge went up to approx 10 psi now (boiler isnt running). When I tap the expansion tank, it sounds half full. What do you think? Was the fill valve stuck? It was just replaced last year. It's apollo model ff. When boiler kicked on, pressure went up to 18.

Note: in the picture you'll see the upstream ball valve closed. Ignore that. I did that just before taking the picture. It was open originally and I returned it to open position after taking the pic.
 

hot_rod

The air pressure in the tank, needs to be adjusted before you fill the system. Charge it to whatever pressure you intend to fill the boiler to, say 12 psi.

If the tank air side pressure is too low, some water will enter the tank. It should be empty when you fill cold.

If too much water goes into the tank cold, you reduce your expansion volume.

EdTheHeaterMan

hot_rod said:

The air pressure in the tank, needs to be adjusted before you fill the system. Charge it to whatever pressure you intend to fill the boiler to, say 12 psi.

If the tank air side pressure is too low, some water will enter the tank. It should be empty when you fill cold.

If too much water goes into the tank cold, you reduce your expansion volume.

Someone needs to make a video of how that procedure should be done. That is not the easiest concept for the average Joe to understand. I wish I could do animated illustrations. (Steve Lav... does a good job but he is a little long winded and does not show the all the possibilities. Maybe I can offer to edit them for him)

Personally, I would connect a hose to a boiler drain valve Close the water feed valve and open the boiler drain. Once the gauge dropped below 12 PSI I would close the boiler drain and take a tire pressure gauge and see what the air pressure in the tank is. If below 10 PSI, I would pump it up to 12 PSI (or 15 or 18 or whatever the system cold fill pressure was). Once that was done, I would open the fill valve and watch the PRV do its thing. If it stopped at the desired pressure… Job done! But that took years of experience to get there.

Draining the old Compression type expansion tank was also hard to understand for the average Joe. One guy that worked for me would just put a hose on the tank drain valve and let all the water out. No air would get in, but the water stopped so it must be drained... right? My shortcut was to place a hose on the boiler drain and drop the pressure in the system. Close the fill valve and open the boiler drain. When the water stopped flowing from the hose I knew the system was under a vacuum. Like when you invert a class in a sink full of water, how the water stays in the glass as you lift it, until you break the surface and all the water runs out. The next step is to open the drain valve on the expansion tank and listen to the air bubble into the tank. In about 3 to 7 minutes the tank would be full of air and you could hear the air bubbles gurgle into the system. That is when I would quickly close the tank drain to stop the air from getting into the loops or radiators. Next is to close the boiler drain valve and open the feed valve. Wait for the water pressure to fill the tank to compress the air to 12 PSI (or what ever the setting was)

hot_rod

Maybe one of the tank manufacturers has a training video at their site, Amtrol, Wessel or Zilmet?
Probably find a You Tube on the procedure.

EBEBRATT-Ed

@fuse_5

Sounds like your feeder was just stuck. This can happen if they seldom have to feed (which is a good thing it shows you have no leaks)

HomerJSmith

As I recall, that lever is a bypass and you should hear water moving thru the valve. It is the nut under that lever that sets the pressure. That lever unscrews and under the tag is the nut.

Dave Carpentier

Is there an approx rule of thumb for adjusting a PRV set pressure ?
If you wanted to drop the applied pressure by say 1 psi, would you turn the nut (or screw depending on the unit) counterclockwise by about 1 turn or could it be 3 turns or ?

Alan (California Radiant) Forbes

Once the gauge dropped below 12 PSI I would close the boiler drain ……  I would pump it up to 12 PSI.

@EdTheHeaterMan  Well done on the description, except I usually leave the boiler drain open while charging the x-tank as I don’t want any pressure building up on the bladder side. 

Water usually gushes out while filling until the bladder reaches the nipple and the pressure starts to build. 

The Milwaukee cordless mini compressor has become one of my favorite tools. I don’t miss my bicycle pump at all. 

EdTheHeaterMan

Dave Carpentier said:

Is there an approx rule of thumb for adjusting a PRV set pressure ?
If you wanted to drop the applied pressure by say 1 psi, would you turn the nut (or screw depending on the unit) counterclockwise by about 1 turn or could it be 3 turns or ?

Nope. You probably get about 5 to 7 pounds per turn, but that changes the more (or less) pressure you apply to the spring inside the valve. You need to feel it. When you get to the pressure you want, (by turning clockwise) past what you need, the boiler pressure gauge will rise slowly. Once the gauge is on the desired PSI, slowly back the screw out (turn counterclockwise) until you hear the water flow stop. You may need a mechanic's stethoscope to hear it, if the boiler room has background noise.

Now you can test by purging 1/2 gallon of water and see if the PRV puts the pressure back where you want it. If not then turn the screw 1/8 of a turn clockwise and see if it stops at the desired pressure. After you do it a few times you get a feel for it.

hot_rod

And some day replace it with a Caleffi 553 Autofill
It is always a fast fill valve. You just set the final pressure you want and the 1/2” valve will fill at 5 gpm. 

No lever, no screws to turn.
As long as you have 30 psi or more on the line pressure. Also available with a good quality gauge so you confirm the actual pressure.

Alan (California Radiant) Forbes

hot_rod said:

And some day replace it with a Caleffi 553 Autofill
It is always a fast fill valve. You just set the final pressure you want and the 1/2” valve will fill at 5 gpm. 

No lever, no screws to turn.
As long as you have 30 psi or more on the line pressure. Also available with a good quality gauge so you confirm the actual pressure.

Never knew that, but I'll still build a bypass around them.

hot_rod

Alan (California Radiant) Forbes said:

hot_rod said:

And some day replace it with a Caleffi 553 Autofill
It is always a fast fill valve. You just set the final pressure you want and the 1/2” valve will fill at 5 gpm. 

No lever, no screws to turn.
As long as you have 30 psi or more on the line pressure. Also available with a good quality gauge so you confirm the actual pressure.

Never knew that, but I'll still build a bypass around them.

It just comes down to how much fill "flow" you want. A 1/2" bypass with 60 psi will flow 10- 12 gpm. So if you are trying to flush multiple loops or large pipe systems, the extra gpm that a bypass provides can help.
As you know, dont turn your back on it

HomerJSmith

The Caleffi auto fill valve is my favorite boiler fill valve. Taco fill valve would come in second. I find that the kind of fill valve that you have hardly regulates below 15 psi.

The acceptance of the Extrol tank is important in how the pressure in the sys varies as registered by the boiler gauge. The air charge on the Extrol tank should match the fill setting of the pressure regulating valve. These tanks do loose pressure over time which reduces the acceptance value and causes the gauge to rapidly increase as the boiler heats up.

Alan (California Radiant) Forbes

Is there any benefit to over-pressurizing an x-tank?  Let’s say to fill it to 22psi on a 15psi system?  Or would the system then just operate at 22psi?

I guess I’m asking if it adds capacity.

Jamie Hall

No benefit at all. in fact, it would ensure that the tank had no capacity to absorb expansion until the pressure of the water rose to the pressure of the precharge.

The system would operate at 22 psi cold -- if you raised the pressure setting of the fill valve to 22 psi. There would be no change in acceptance capacity in gallons, but the pressure change from cold to hot would be greater.

EdTheHeaterMan

The compression tank (the air portion) already has 22 PSI inside it so you need to put more that 22 PSI water pressure in the boiler before you start to fill the tank with any water. If you are thinking of using the combined water pressure of the house water pressure plus the water in the tank to offer you a longer initial push to force water to entrain the air from the third floor, then you are probably shooting yourself in the foot. At say 26 PSI there will be less volume of water in the tank to add to the fast fill flush. I believe leaving it at the desired static fill pressure for purging will get you the best result.

As you add pressure to the system to say 26 PSI to start the purge... there will be more water in the tank and the extra water will help to maintain the initial pressure for a few gallons longer. The entrained air will get back to the basement on the first push.

fuse_5

Hello guys ... thank you so much for all the details and the lively discussion! Some of the things you mentioned are good but a bit over my expertise level. Do I really need to drain and refill the tank? All I did was move the lever on the prv and it jacked up the boiler pressure to approx 14 psi now (about 18 when boiler is running) I did not drain anything. My guess is the prv was stuck but I am thinking the boiler is good to go now that the pressure is where it needs to be. Am I correct? Or should I call a plumber?

By the way, for verifying the pressure gauge is accurate, I was not able to find a bib gauge at menards that fits my drain valve. My drain valve is 1 inch with threads on the outside. The bib gauges at Menards mostly had threads on the outside and were smaller diameter for the most part. 

hot_rod

Alan (California Radiant) Forbes said:

Is there any benefit to over-pressurizing an x-tank?  Let’s say to fill it to 22psi on a 15psi system?  Or would the system then just operate at 22psi?

I guess I’m asking if it adds capacity.

In some cases we do the opposite, have the air pressure a bit lower then fill pressure. Solar thermal and chilled water systems. As the fluid drops in temperature, in solar piping in winter month, or chilled water systems filled with room temperature water.
As fluid cools the contraction causes a drop in system pressure, possibly to zero. So a bit of over pressurization assures you always have NPSHa, and pressure on the gauge

Tank may need to be upsized if you add this "safety seal"

Alan (California Radiant) Forbes

@fuse_5 I believe this is what @HomerJSmith is talking about:

https://www.supplyhouse.com/Zurn-HGI-25-Hose-Bibb-Pressure-Gauge-with-Maximum-Pressure-Indicator

It screws onto a boiler drain or hose bibb. I don't see any in your photo - it might be hidden.

EdTheHeaterMan

fuse_5 said:

Hello guys ... thank you so much for all the details and the lively discussion! Some of the things you mentioned are good but a bit over my expertise level. Do I really need to drain and refill the tank? All I did was move the lever on the prv and it jacked up the boiler pressure to approx 14 psi now (about 18 when boiler is running) I did not drain anything. My guess is the prv was stuck but I am thinking the boiler is good to go now that the pressure is where it needs to be. Am I correct? Or should I call a plumber?

By the way, for verifying the pressure gauge is accurate, I was not able to find a bib gauge at menards that fits my drain valve. My drain valve is 1 inch with threads on the outside. The bib gauges at Menards mostly had threads on the outside and were smaller diameter for the most part. 

You do not need to check the air pressure in the expansion tank. Starting at 14 PSI cold and topping off at 18 PSI hot is well within the operating range of the system. Your expansion tank is just fine.

The Bibb gauge is for attaching to a garden hose connection. The boiler drain valve at the bottom of the boiler is a good place to try it. But I would do it when the boiler is cold and open it to make sure that water comes out (not plugged with boiler bottom deposits) with no sludge. If the water flows dirty for a second or two then clear, you are good to go. After you test the water flow... close the valve... screw on the gauge... open the valve.

hot_rod

Those hose connection gauges are very handy for all sorts of pressure testing.
For hydronic work, it’s nice to swap to a 30 psi gauge. 200 psi is a bit coarse of a scale to read accurately below 20. It’s a standard 1/4 not thread to swap other gauges.

fuse_5

Thank you once again for the details and links! I was envisioning the gauge to be just like what's on the link but menards didn't have anything like it. I may need to get it from a plumbing supply store instead of a hardware store. I do know that my drain valve has a 1 inch diameter instead of the standard 3/4. I measured it with a caliper. And also thank you for the directions on how to measure the pressure. You guys rock!! I'm glad I found this forum!

EdTheHeaterMan

fuse_5 said:

Thank you once again for the details and links! I was envisioning the gauge to be just like what's on the link but menards didn't have anything like it. I may need to get it from a plumbing supply store instead of a hardware store. I do know that my drain valve has a 1 inch diameter instead of the standard 3/4. I measured it with a caliper. And also thank you for the directions on how to measure the pressure. You guys rock!! I'm glad I found this forum!

ID or OD?

JUGHNE

fuse 5, just try a hose fitting on it to see what you got.

vhauk

those those low pressure prvs can be troublesome. Both the pressure reducing valve and the pressure relief valve. 

fuse_5

Outside diameter 1 inch (including the threads) I'll try a hose fitting and see. Thanks