Pressure check of expansion tank

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  #1  
Old 03-21-20, 02:34 PM
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Pressure check of expansion tank

Recently replaced my expansion tank it is an amtrol and it was precharged at 12psi. My feed valve pressure I'm not 100% sure what the pressure is. I think the feed valve may be faulty. My question is can I get an idea of feed valve pressure by feeling the expansion tank for heat? My thinking was that if the feed valve and expansion tank are both at 12psi then I should feel heat half way down the expansion tank? Right now I'm only feeling heat at the very top of the expansion tank which I was thinking meant the expansion tank is at a higher pressure than the feed valve.
 
  #2  
Old 03-21-20, 03:03 PM
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You cannot check your pressure the way you described. Yiur expansion tank has an air bladder in the bootom half of the tank which is precharged to 12 psi and does not allow the water to enter that part. Only the top half has water when it's heated and when the water cools goes back into the sysytem. If your tank gets full of water that means your bladder has ruptured and must be rplaced.

Let your boiler cool down and see the pressure gauge reads. If you still think it's off then get another gauge and screw it on to your boiler drain and see if it matches.

Hope this helps a little.

 
  #3  
Old 03-21-20, 03:27 PM
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ok, was thinking that wasn't a good way to check... sure would be nice to be able to check that way though instead of having to drain the boiler.

what made me wonder something was up was only the very tip top of the expansion tank is hot, the sides all the way to the top are cool to the touch making me think the pressure in expansion tank was too high.
 
  #4  
Old 03-21-20, 05:08 PM
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You do not have to drain the boiler. Just let it cool down to check the boiler gauge. That's if your feed valve hasn't been adjusted to a higher pressure when installed.

To add a second gauge just get one with a hose fitting and screw it on to a drain valve on the boiler and then open the valve to read and then close when done.

No draining is necessary.

In a perfect world they want your feed valve pressure and extrol pressure to be set the same but nobdy ever does and it doesn't seem to have any effect on the operation of the system. I run my boiler at 20 psi and my tank is at 12 psi for over 30 yrs. with no problems.
 
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  #5  
Old 03-21-20, 07:19 PM
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First thing to do is verify actual boil pressure. The majority of boiler pressure gauges are defective or inaccurate.
The original boiler gauges are often junk.

I installed a second 4" gauge as back up.

DIY post by NJT on 02-09-12 is a must read on hydronic system gauges:

How to verify a boiler pressure gauge

https://www.doityourself.com/forum/b...ure-gauge.html
 
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  #6  
Old 03-22-20, 12:03 PM
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Thank you for the responses spott and doughess! When I verify the boiler gauge at boiler drain, I find that the original boiler temp/pressure gauge definitely does not appear to be correct (seem to indicating too high at 22 psi and 225F when the boiler drain gauge is indicating 15 psi

What I notice is that it is 15 psi at boiler drain. There are other drains located above each zone control valve which is about 3 1/2 feet higher than the boiler drain and the pressure I get there is 13 psi. Does this sound correct?

The pressure when boiler is operating seems to be okay, only rising a few psi when boiler is hot so my new expansion tank seems to be doing its job.

I have noticed some water leaking from pressure relief valve, not a lot and only occasionally, so now I'm thinking it is bad and is what is causing my noisy boiler.

doughess, when you say you installed a 4" gauge as a backup is that backup installed at the boiler drain?

Thanks for your help!


 
  #7  
Old 03-22-20, 04:05 PM
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K,
If your relief valve is dripping or leaking that means your boiler is approaching 30 psi which means something is not doing its job.

You either have a tank with a ruptured bladder or needs a charge. You can only check your tank when it's isolated from the system, either by a valve installed between the tank and the system or removing the tank. Otherwise you will be reading system pressure.

The other thing you might look at is your feed valve. It may be leaking by. If you suspect this shut off the manual valve for the boiler and see what happens. You can also feel the temp of the boiler feed line. It should be room temp or there abouts. If it's cold that means fresh water is leaking by.
 
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  #8  
Old 03-22-20, 07:17 PM
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Re kettlin-1 Would not worry about small differences in pressure at points in system.

With properly sized expansion tanks pressure should not vary more than a couple of pounds over wide range of water temperatures. The calculators for sizing tanks are often incorrect. Size of tank depends on volume of water in system, BTU rating of boiler is only rough gauge of that. My old system holds 30 gallons of water. Fired at 90,000 BTU needs 60 gallon expansion tank for stable pressure.

A common cause of leaking pressure relief valves is rust particles and other debris in fresh water feed. To reduce problem installed whole house water filter with clear plastic housing in feed to hot water tank and hydronic system. Yes, 30 PSI will result in water release but that is what valve is designed for, but at 12 PSI indicates a problem and not one of high pressure.

I have pressure regulator/relief assembly installed with unions on either side of it and shut off valve. It can be easily removed for service while rest of system is kept pressurized to keep heating system operational. The second 4” gauge (now primary reference) is between that shut off valve and boiler. Am big on having heat on cold winter nights.
 
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Last edited by doughess; 03-22-20 at 07:50 PM.
  #9  
Old 03-23-20, 08:28 AM
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In order to reset the expansion tank without draining the boiler at all you need three valves at the pressure tank:
1. Between the expansion tank neck and the fresh water feed,
2. Between the expansion tank neck and the rest of the system,
3. In the expansion tank neck to the outside (spigot).

If the fresh water feed is some distance away then you only need valves #2 and #3 at the tank.

After closing #1 and #3, open #2 and then reset the expansion tank to the desired pressure (typically around 12 PSI for a heating boiler).
 
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  #10  
Old 03-23-20, 07:04 PM
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A major issue when connecting gauges to drains is debris when valve is opened.

Recommend flushing water from valve before attaching gauge.

For temporary gauges prefer to use short length of hose with gauge positioned at top of "U" with stem at bottom.

For permanently mounted gauge chose location that avoids debris.
 
  #11  
Old 03-25-20, 08:35 AM
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My feed valve is on track to be delivered today. Ordered some valves and pressure relief valve and should be delivered tomorrow. Hopefully this weekend I will have all this back together with valves in the locations you suggested so I can replace or test components without having to drain the boiler! Thanks for all the help and suggestions!

The only other thing that I can think of that may be causing a problem is the aquastat. It was set to 190 so I turned it down to 180. Could the temp sensor on it be shot and not turning the burner off when it should. My Boiler temp/pressure gauge can't be trusted so that will be something I replace this weekend too.
 
  #12  
Old 03-25-20, 09:49 AM
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If one of Kettlin-1's problems is temperature control, Out-DOOR-RESET contacts can be used to replace just that function leaving other control functions in place. That can be simpler than redoing everything.

Old technology aquatats are frequent boiler problem that can be remedied by using a modern ODR as aquastat. The Tekmar 256 for $157 is a best buy and ODRs provide many other features and benefits.
https://www.supplyhouse.com/Tekmar-2...xoCNrMQAvD_BwE

A basic aqustat is a simple temperature activated switch, but many things called “aqustat” are actually multi functional and are also burner primary control, circulatory control and 24 VAC power source.

A simple aquastat:
https://www.supplyhouse.com/sh/contr...well+aquastats

A multi function aquastat:

https://www.supplyhouse.com/Honeywel...hoC058QAvD_BwE
 

Last edited by doughess; 03-25-20 at 11:15 AM.
  #13  
Old 03-25-20, 02:40 PM
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K,
Your aquastat being off a few degrees one way or another will not cause your pressure problems. Your boiler is made to operate at those temps. As long as your expansion tank is sized properly your aquastat settings are fine. It is true that the higher the temp, the higher the pressure but that is what your extrol tank is there for.
 
 

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