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# Slantfin Pressure question

#1
10-26-18, 12:45 PM
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Join Date: Mar 2018
Location: United States
Posts: 35
Slantfin Pressure question

My brother and I replaced a reducing T in the return manifold due to corrosion and leak. I bled the system and standalone pressure gauge read 18.5 psi & boiler gauge 22 psi.
Im new at this so I’m learning as I go. This morning with a cold boiler the pressure was 6psi and my expansion tank is new and adjusted to 15 psi. Previously with cold boiler it was 15 psi.
This morning I bled the system again. I adjusted pressure to 16 psi cold on my standalone pressure gauge, after warmed up 20 psi standalone pressure gauge and boiler gauge 25psi.
I started with 1-1/2 gallons of antifreeze for bleeding and when I finished I had 1-1/2 gallons.
Is the volume of the system that sensitive that a couple ounces will affect cold pressure?
Should I have just added antifreeze on the cold boiler to attain 15 psi on standalone pressure gauge?

#2
10-26-18, 02:29 PM
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Join Date: Oct 2008
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You need to determine which gauge is correct - maybe neither is? With 5 psi difference, you are flying blind.

#3
10-26-18, 04:33 PM
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Join Date: Mar 2018
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I added the 2nd gauge because many claim the combo gauge are incorrect.
But you didn’t answer my basic question. What should the lowest pressure be?
Shouldn't it be the expansion tank pressure?
regards

#4
10-26-18, 05:42 PM
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Join Date: Oct 2008
Location: USA
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What should the lowest pressure be?
Shouldn't it be the expansion tank pressure?
When you say the "lowest," are you talking about the lower of the two gauges? But, to answer your question, the pressure of the air side of the expansion tank should, under most circumstances, be equal to the water side. One or both of your gauges is wrong, and you need to determine that.

Why are you using antifreeze?

#5
10-26-18, 06:22 PM
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Join Date: Mar 2018
Location: United States
Posts: 35
Im at a loss. Before repair cold pressure equaled expansion tank pressure of 15 psi. Now it’s low cold, but normal hot. If I add more water it will raise hot pressure.

Syatem had antifreeze, cold climate in case of power or propane outage.
regards.

#6
10-26-18, 06:29 PM
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Join Date: Oct 2008
Location: USA
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I think the first thing you need to do is to figure out which gauge, if either, is correct. They need to be tested or a third gauge compared. When you have two gauges that significantly differ, there is no logical way to tell which one, if either, is correct.

#7
10-27-18, 04:20 AM
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Join Date: Mar 2018
Location: United States
Posts: 35
Checked both gauges this morning with a cold boiler and they both read zero pressure. I can only think of two possible causes. The Spirovent bled some air out causing the pressure to drop or my expansion tank isn’t working correctly?
i understand the gauges have a 5 psi difference but the newer one never dropped below 15psi prior to fitting repair.
I live in the boonies and will eventually get another gauge to check pressure.

#8
10-27-18, 09:14 AM
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Location: USA
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This is strange. Do you have an automatic fill valve (a.k.a. pressure reducing valve) that is connected to your domestic water supply? Whenever the system pressure drops below the setpoint, it should automatically add water to your boiler. I'm mystified how the pressure dropped to zero - unless there is a major leak from your system.

#9
10-27-18, 09:41 AM
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Join Date: Mar 2018
Location: United States
Posts: 35
Got it figured out. Read some articles and my Extol tank pressure which I set to 15 psi should be 12 psi according to the chart and height of my 2nd floor. I lowered to 12 psi.

Then I read articles about the automatic fill valve which was turned off. I had put a kit in my Watts series 009 but it still weeps water out top bleed. I also learn fill valve is set to 12 psi, so I opened water supply to Watts and allowed regulator to fill cold to 12 psi and my second gauge verified 12 psi.

My my only mistake is I should of manually opened all zone valves when cold and allowed 12 psi fill thru the whole system.

My boiler vent was seeping antifreeze and I tapped on it and it stopped. Time for new or cleaning?

https://inspectapedia.com/heat/Expan...e_Settings.php

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

regards

#10
10-27-18, 02:01 PM
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Join Date: Oct 2008
Location: USA
Posts: 2,925
OK, I think you are about out of the woods.

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