bad boiler gauge? or?

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  #1  
Old 11-03-13, 01:21 AM
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bad boiler gauge? or?

Hello.

I've been fighting with a boiler issue, when it reaches its set temperature of 180 degrees, just after the burners go off the gauge is showing 20-25 psi then slowly rises to over 30 psi, sometimes even 40 psi but the PRV never opens or leaks.

I have open/closed the PRV manually a few times and even managed to accidentally force it open by leaving the fastfill on the fill valve open. So I know it works.

I drained the system and replaced the fill valve and expansion tank. (old fill valve was faulty, not filling system with normal setting)

But the problem persists, gauge still rises to 30-40psi after burners turns off.

The heat is working fine at every radiator and operates normally.

Should I be concerned about this gauge reading? The boiler says 30psi max on it. The only thing i haven't replaced is the flow control valve.


Some pictures....





PRV label


Fill valve label


expansion tank label



Gauge@ cold


gauge@ burners off


gauge@ few minutes after burners off
 
  #2  
Old 11-03-13, 07:49 AM
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Is the line from the expansion tank connected to the red flo-control valve? That is unusual.

There is a "sticky" on this forum that explains how to check the gauge. Otherwise, I would just replace it. The scale on the pressure gauge is not very good for reading the pressure.

Did you check the air charge in the new expansion tank before pressurizing the water side?
 

Last edited by gilmorrie; 11-03-13 at 08:19 AM.
  #3  
Old 11-03-13, 10:19 AM
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Here is the post Gilmorrie is referring to:

http://www.doityourself.com/forum/bo...ure-gauge.html

It's highly possible that your gauge is reading wrong.

accidentally force it open by leaving the fastfill on the fill valve open.
Did you happen to notice what the gauge was reading when this occurred?

As an FYI, you should also read this one:

http://www.doityourself.com/forum/bo...sion-tank.html

There are step by step for properly charging the air in a tank when needed... which should be BI-ANNUALLY at the minimum. The most important thing to understand about the process of charging and checking the air in the tank is that there can be NO PRESSURE on the water side while doing so.

At some point you may wish to add the additional valve that are shown in the sticky post to make servicing the tank a 10 minute job...

The connection of the tank at that location is not a problem.

There is no reason to have to change the flow control valve. It's just a weighted disc inside that lifts when the pump turns on. If you are getting heat properly, and not getting heat from 'ghost flow' when the system is off, then the valve is functioning properly.
 
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Old 11-03-13, 10:21 AM
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What is strange about the pics is that when the temperature is HIGHER, the pressure is LOWER. This is completely reverse of what you should be seeing!

Yes, check the gauge first.
 
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Old 11-03-13, 12:29 PM
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No i didn't check the expansion tank.. i just picked it up at home depot and hooked it up, I did check the old one before removing it and it was fine. I now realize i should've installed a valve and drain

I've heard they are filled with nitrogen at the factory and just checking the pressure can lower it.

I did check the pressure when the PRV opened that one time and it was between 0-10 (iirc)... also the gauge seems very slow to respond.

I think the mains pressure is somewhere around 55psi

I managed to get this picture last night. This was after 2 consecutive burns. And again the PRV valve never opens or leaks. I checked a couple radiators for air again.. just straight water. No strange noises or anything to cause alarm... aquastat was/is set to 180




Also a bit more info about the system.. boiler is from 1995 and its a two story home.


I will try to build one of those test gauges, thanks guys!
 

Last edited by tocaedit; 11-03-13 at 02:34 PM.
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Old 11-03-13, 12:40 PM
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No i didn't check the expansion tank..
The gas naturally diffuses through the bladder. This would occur even if it were inflated at the factory and spent time before you purchased it. I don't know if it would have been inflated with pure nitrogen (air itself is about 80% nitrogen). Yes, checking it with a tire gauge will cause a tiny bit of the gas to leak, but not enough to worry about. But, you can measure it twice and see if there is any significant difference. But, how else can you check it?

I recommend you depressurize the water side of the expansion tank and check the pressure.
 
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Old 11-03-13, 01:51 PM
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The scale on the pressure gauge is not very good for reading the pressure.
Those boiler "tridicator" gauges seldom have sufficient range and resolution for measuring pressure accurately. This is a 3.5", 0-30 psi gauge with 1 psi increments that can be installed near the boiler, but not necessarily on the boiler. I can easily read pressure within 0.5 psi.

 
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Old 11-03-13, 04:06 PM
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I doubt the Nitrogen story myself... I seriously doubt that a manufacturer would add any extra cost to manufacturing the tanks... knowing full well that service guys aren't going to carry an N2 tank on their truck to recharge the tanks in the field.

I now realize i should've installed a valve and drain
As long as you've got room under the tank, you can always do that later...

I did check the pressure when the PRV opened that one time and it was between 0-10 (iirc)... also the gauge seems very slow to respond.
Yeah... something wrong with that gauge. No way the relief valve could have opened THAT low!

OK, you've got your marching orders, let us know what you find!
 
 

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