Ideas for reducing home boiler PSI

[Greg Bernhardt]

TL;DR Summary

Home water boiler reading higher than normal PSI. How to reduce?

I have a two-story house with a 30-year-old water boiler rated for a max of 40 PSI. When the system is cold it rests at about 18-20 PSI and when fully hot it sits around 30-32 PSI. I had a tech come and take a look because I read somewhere PSI should be around 15. The tech said my gauge might just be faulty. Said even if too high it will just trip the pressure valve. Said it should trip around 30 and I said I never saw any evidence of water and that was why he thought the gauge might be faulty because I did have the valve replaced a few years ago but never tested. Anyway, the tech didn't seem too bothered but it's making me paranoid. I bled a mixing bowl of water out of a radiator and the pressure didn't drop noticeably maybe I need to drain much more or maybe the tech is right and the gauge is all wrong. Anyway, maybe time for a second opinion?

 

[Lnewqban]

Copied from
https://www.boilercentral.com/troubleshooting/7-reasons-why-your-boiler-pressure-is-too-high-or-low/

“To diagnose this problem, you simply shut the boiler off and see what the pressure gauge says. If the boiler pressure gauge reads 1.5 or more, then you likely have too much water in the system.”

Also, if you close the shut-off valve supplying the house and open any faucet until no water comes out, that old gauge should indicate zero.
If not, the poor thing is not reading the water pressure properly.

 

[Greg Bernhardt]

“To diagnose this problem, you simply shut the boiler off and see what the pressure gauge says. If the boiler pressure gauge reads 1.5 or more, then you likely have too much water in the system.”

And the system has to be completely dead cold right? This will be different than when I've looked at the gauge when I've felt the pipes cold and not turned the boiler "off"?

Also 1.5 bar is 21psi right? huh, that sounds like what I've seen.

 

[Lnewqban]

And the system has to be completely dead cold right? This will be different than when I've looked at the gauge when I've felt the pipes cold and not turned the boiler "off"?

My gauge also isn't like on that webpage. So I don't know what 1.5 equates to in PSI.

It seems that the article implies that not enough trapped air cushion in the whole system may interfere with the natural expansion of the water when hottest, abnormally increasing the pressure.

I would first verify how off the gauge is, if the needle is moving at all.
Many old gauges get stuck in one extreme position.

 

[Greg Bernhardt]

I would first verify how off the gauge is, if the needle is moving at all.

It moves from about 20 when cold to 30+ when hot, not stuck.

 

[Tom.G]

They are cheap (relative to the consequences), replace the gauge.

You did not say whether it is a steam or a hot water heating system. If steam, it is best to get on the problem right away, you do NOT want a 30 or 40 psi steam explosion; much/all the water in the system would likely flash-boil due to the rapid pressure reduction.

A contributing factor to not enough air space could be scale & sediment build-up in the boiler (of course a leaking inlet valve may contribute). In severe cases you often hear the water boiling during the heating cycle because convection is reduced by the sediment. I've seen old domestic hot water heaters that were 2/3 full of scale & sediment. (makes it extra hard on the plumber getting the old heater out to their truck for disposal)

Any how, a complete inspection may be needed.

Cheers,
Tom

 

[Greg Bernhardt]

hot water heating system

hot water

I've seen old domestic hot water heaters that were 2/3 full of scale & sediment.

I did have the system drained about 6 years ago that helps?

 

[russ_watters]

I'm not as big into hydronic systems (especially residential), but I would expect the pressure is set by an expansion tank. @Greg Bernhardt do you know if you have an expansion tank? Is there a rating sticker on it? How old is it? Maybe it needs to be recharged/replaced? It should look like this:
https://www.homedepot.com/p/Amtrol-No-30-Expansion-Tank-for-Hydronic-Boiler-EX-30/202268962

FYI, because of the expansion tank, bleeding air or draining a bit of water will not have a significant impact on pressure (when you drain it you're emptying a lot out of the expansion tank before the pressure drops significantly). Related question though: does it have an automatic fill or manual fill? If automatic, the regulator would control the pressure. But in a closed system this should not be needed.

 

[Greg Bernhardt]

I'm not as big into hydronic systems (especially residential), but I would expect the pressure is set by an expansion tank. @Greg Bernhardt do you know if you have an expansion tank?

Oh yes, I got it replaced last year.

 

[bigfooted]

If this is a closed water circuit, and you fill your system with fresh water, then the dissolved air in the water tends to form air bubbles over time. When you then heat the water+trapped air, these heated air bubbles cause a much larger increase in pressure. In my home we have air release valves at every radiator, you just open them with a small tool and any local air bubbles can escape. After refilling the entire system with fresh water, it can take a couple of months to get rid of all the air. If you have a lot of air in your circuit, you can often hear it sloshing around, making gurgling sounds.
A problem that is less frequent is the return temperature of the water being too high and the water starts boiling when it gets reheated. Here, the heated water is around 70-80 degrees Celsius and the return temperature of the water is around 50-60 degrees.

 

[Tom.G]

I did have the system drained about 6 years ago that helps?

Yup, -- unless your water is exceptionally hard or dirty.

 

[chemisttree]

PSIA or PSIG?

 

[Spinnor]

With the system cold you might check the pre-charge on the expansion tank. I think it should be several psi below cold system pressure. There should be a place on one end to check the pressure with a tire pressure gauge. If the pressure is too low or high the expansion tank won't act as needed.

Edit, if the expansion tank is working properly the pre-charge can be higher then system pressure but can't be lower as water would enter the expansion tank until pressures equalized across the expansion tank bladder.

See,

how to test the expansion tank in your hydronic heating system​

See,

Expansion Tank Pre Charge Pressure​

https://forum.heatinghelp.com/discussion/112388/expansion-tank-pre-charge-pressure

From Google search, "how to set the furnace expansion tank pressure precharge"

https://www.google.com/search?q=how+to+set+the+furnace+expansion+tank+pressure+precharge&sca_esv=588752686&sxsrf=AM9HkKmm7NNJL6c6lrcBwN1uJfXdkY-LbQ:1701959682090&ei=AthxZZiYBeGIptQPqIab8As&ved=0ahUKEwiYoZfyxf2CAxVhhIkEHSjDBr4Q4dUDCBA&uact=5&oq=how+to+set+the+furnace+expansion+tank+pressure+precharge&gs_lp=Egxnd3Mtd2l6LXNlcnAiOGhvdyB0byBzZXQgdGhlIGZ1cm5hY2UgZXhwYW5zaW9uIHRhbmsgcHJlc3N1cmUgcHJlY2hhcmdlSABQAFgAcAB4AZABAJgBAKABAKoBALgBA8gBAPgBAeIDBBgAIEE&sclient=gws-wiz-serp

See also (maybe the best explanation),

Heating Boiler Expansion Tank Pressure Adjustment​

https://inspectapedia.com/heat/Expansion_Tank_Pressure_Settings.php

 

[Greg Bernhardt]

Nice video @Spinnor! I tapped the expansion tank and it appears to sound like it should if working. My release valve is set to 30 psi but not water seen.

I took a photo of my pressure gauge this morning.

 

[Spinnor]

With the system cold you might check the pre-charge on the expansion tank. I think it should be several psi below cold system pressure. There should be a place on one end to check the pressure with a tire pressure gauge. If the pressure is too low or high the expansion tank won't act as needed.

Edit, if the expansion tank is working properly the pre-charge can be higher then system pressure but can't be lower as water would enter the expansion tank until pressures equalized across the expansion tank bladder.

See,

how to test the expansion tank in your hydronic heating system​

See,

Expansion Tank Pre Charge Pressure​

https://forum.heatinghelp.com/discussion/112388/expansion-tank-pre-charge-pressure

From Google search, "how to set the furnace expansion tank pressure precharge"

https://www.google.com/search?q=how+to+set+the+furnace+expansion+tank+pressure+precharge&sca_esv=588752686&sxsrf=AM9HkKmm7NNJL6c6lrcBwN1uJfXdkY-LbQ:1701959682090&ei=AthxZZiYBeGIptQPqIab8As&ved=0ahUKEwiYoZfyxf2CAxVhhIkEHSjDBr4Q4dUDCBA&uact=5&oq=how+to+set+the+furnace+expansion+tank+pressure+precharge&gs_lp=Egxnd3Mtd2l6LXNlcnAiOGhvdyB0byBzZXQgdGhlIGZ1cm5hY2UgZXhwYW5zaW9uIHRhbmsgcHJlc3N1cmUgcHJlY2hhcmdlSABQAFgAcAB4AZABAJgBAKABAKoBALgBA8gBAPgBAeIDBBgAIEE&sclient=gws-wiz-serp

See also (maybe the best explanation),

Heating Boiler Expansion Tank Pressure Adjustment​

https://inspectapedia.com/heat/Expansion_Tank_Pressure_Settings.php

So I did the steps in

https://inspectapedia.com/heat/Expansion_Tank_Pressure_Settings.php

With boiler cold, furnace pressure and expansion tank 15 psi. Close off furnace water supply and then drain about 1/2 gallon of water until furnace pressure drops to 11 psi. Expansion tank now reads 12 psi.

 

[Spinnor]

A typical circulator pump performance is curve 5 below,

My circulator pump is on the inlet side of the furnace, normally it is on the supply side. With the pump on the inlet side and flow rate set low by the furnace flow valve you could add 4 psi to your system pressure when the circulator turns on. That is only a small amount of your over-pressure, likely not the issue.

Is your expansion tank mounted so the pressure check valve is on the bottom? If so if there was water in the expansion tank past the bladder you would know when you checked the pressure and you noticed none.

There are several types of hot water radiators, is yours low volume or high volume type (the really old fashion types are high volume and 3/4 inch copper tube base board types are low volume)?

Does your furnace have a low-water cut-off switch? If not I would be paranoid leaving my house with the furnace on with the numbers your furnace is showing. If the first furnace tech is not concerned maybe time to bring in another.

A picture or two of your furnace wouldn't hurt and the solution to your problem when you get it fixed.

 

[Greg Bernhardt]

 

[Greg Bernhardt]

I turned the water valve off above the pressure regulator and drained 1/2 gallon from a radiator. Appears to have dropped the PSI a few. I suppose that is the key if bleeding is to kill the water intake otherwise is just refills? I guess that could be the issue is the pressure valve is set wrong? hmm it was just replaced though.

 

[Lnewqban]

I guess that could be the issue is the pressure valve is set wrong? hmm it was just replaced though.

Can the relief valve be opened by hand?

 

[Greg Bernhardt]

Can the relief valve be opened by hand?

I'm sorry, I mean the water intake pressure regulator.

 

[Spinnor]

I turned the water valve off above the pressure regulator and drained 1/2 gallon from a radiator. Appears to have dropped the PSI a few. I suppose that is the key if bleeding is to kill the water intake otherwise is just refills? I guess that could be the issue is the pressure valve is set wrong? hmm it was just replaced though.

When the system is cold the pressure is where it should be. (how many stories above the furnace?) It is only when the system reaches its max temp that the pressure reads high and above the red mark at 30 psi. Your tech shrugged it off as a possible faulty pressure valve if I recall. He should have said "If it were my furnace I would take the time and get to the bottom of things. Lets try replacing the pressure valve and see if that fixes things".

A Pro would quickly formulate a list of things to check, easy and most likely problem checked first. So replacing the valve might not be the logical first step.

Maybe he had somewhere else to be?

There is a fairly active home improvement sub forum, HAVC here,

https://www.diychatroom.com/forums/hvac.17/

If you are not ready to give it over to a "Pro".

 

[Greg Bernhardt]

I scheduled a visit from a different company to take a look later this week.

 

[Lnewqban]

What fi

I'm sorry, I mean the water intake pressure regulator.

What figure best describes your system?

https://uticaboilers.com/wp-content/uploads/2022/02/1798.pdf

Where is the circulation pump located at?

 

[Greg Bernhardt]

What fi

What figure best describes your system?

https://uticaboilers.com/wp-content/uploads/2022/02/1798.pdf

Where is the circulation pump located at?

yep that's what it looks like! I think one is near the boiler and another in a side room in the basement

 

[Tom.G]

Just stumbled across this video on Hot Water heating systems. Not directly applicable but much varied info, a bit 'chatty'.



edit:
Another one, How to Set Pressure: (haven't watched it)

 

[russ_watters]

I'm not sure there is an actual problem here. I get that the pressure is above the recommended value, but is it actually causing a problem? Sure, you can probably reduce the pressure by taking a little bit of water out of the system or air out of the expansion tank, but what problem would that solve other than getting the needle back on the design pressure line?

 

[Greg Bernhardt]

I'm not sure there is an actual problem here. I get that the pressure is above the recommended value, but is it actually causing a problem? Sure, you can probably reduce the pressure by taking a little bit of water out of the system or air out of the expansion tank, but what problem would that solve other than getting the needle back on the design pressure line?

If the gauge is reading correctly, I am assuming the extra pressure is wearing the system down faster, and at some point, the issue will be one I would have rather mitigated from the beginning. 5PSI from the max the system was designed for doesn't seem like something I want to be flirting with considering the pipes are 100 years old too.

 

[russ_watters]

If the gauge is reading correctly, I am assuming the extra pressure is wearing the system down faster, and at some point, the issue will be one I would have rather mitigated from the beginning. 5PSI from the max the system was designed for doesn't seem like something I want to be flirting with considering the pipes are 100 years old too.

Ehh, kinda. The system is designed for what is needed to do its job, which is 30psi. The safety relief valve set pressure is 40psi because 'why bother setting it higher'. The system will not fail if the pressure goes up to 45 psi and the SRV doesn't open. The difference in "safety" is negligible unless your system operates near its maximum allowable pressure, which is not the design pressure.

Your boiler nameplate says its maximum allowable working pressure is 100 psi and the lowest rating I'm familiar with for piping and fittings is 125 psi. So while it is technically true that higher than necessary pressure can cause early failure, 35psi is way, way below what the system is likely capable.

The first things that would be expected to go are parts that move or are exposed to fire. I guess a slightly higher than necessary pressure would cause something that's rusting-out to fail sooner (not deteriorate faster), but I doubt the difference is going to be significant.

But if it gives you peace of mind for a nominal fee, it's fine to have it adjusted.