natural gas boiler high psi damage?


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Old 01-27-07, 08:04 AM
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natural gas boiler high psi damage?

Hello. I am new here and would just like to say that I have spent a good couple of hours scouring this forum as well as others before posting my question.

That being said, I have a CG4 series Weil Mclain boiler. Recently i have started seeing the pressure rise from resting cold psi (12) to close to 30 PSI operating at around 140 degrees F. the T&P relief valve is weeping, more decidedly so the closer it gets to 30.

From reading the forums, I am going to be targeting the expansion tank (WATTS ET-15) and the PRV (pressure reducing valve) for malfunctions, and I would like to thank this forum for pointing me in those directions...

I have also read that the tankless coil? could also be at fault here if the others are ok.

Could someone explain the function of the tankless coil?

also, I am not interested in ruining my system by running it at 30 PSI until I get a chance to either fix it or have it fixed. Can someone expand a little on the damage that could be cause by continuing to run the system?

Potentially, if I could not get it looked at before monday or tuesday (today being saturday) do I run the risk of ruining the whole system (i know there is always a risk, but let's say a "probability")

Many thanks for your help
 
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Old 01-27-07, 08:28 AM
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A "tankless coil" is a means of heating the domestic hot water by passing the domestic water through a coil of tubing that is immersed within the boiler proper. Is your domestic hot water heated by the boiler or is it supplied by a completely separate water heater, either electric or gas fired?

Since the boiler pressure is 12 psi when cold it is unlikely that the PRV is the problem. Most likely you have an expansion tank that has lost its air charge. This may be the result of the inner diaphragm leaking or (unlikely but possible) the air has leaked ouot of the tire pump filler valve.

You do not have a "T&P" valve on the boiler as it is actuated by pressure only. T&P is a "Temperature & Pressure" activated valve and is found on domestic water heaters.
 
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Old 01-27-07, 08:33 AM
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I recently read that the diaphragm type tanks can lose about 1 PSI per year due to the fact that the air can pass through the bladder. That would mean if your tank is like 12 years old, there might be no air in it just for that reason. But, a 12 year old tank is probably ripe for replacement anyway. I don't think your system is that old though, is it ?

Is there a valve between the scoop and the exp tank ?

You won't ruin it, but you do run the risk of personal and property damage from hot water escaping the relief valve. You could release a bit of the pressure until you have a chance to have it looked at...
 
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Old 01-27-07, 08:48 AM
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Furd and NJ... thanks for clarifying a few things. Sorry about calling the Pressure relief valve a T&P. thanks for correcting me. Additionally, NJTrooper, If i read everything correctly, my system was installed in 1994 (prior to me living here), so your 12 year hypothesis might be right. There is a valve between the air scoop (still researching what that is) and the expansion tank, which i think will make replacing easier.

for a novice how hard is it replacing the expansion tank? I am mechanically inclined but have not done a whole lot of plumbing (i have put in new sinks and such)... it sounds like this is doable for someone like me....
 
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Old 01-27-07, 02:20 PM
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Just want to make sure I am thinking about this correctly.

1. Depressurize system (allow to sit until showing 12 PSI),
2. Turn off Feed valve
3. Drain System to reduce pressure to O
4. Tighten valve on pipe leading to expansion tank to isolate it from rest of system...
5. Unscrew expansion tank
6. Either repressurize or replace tank
7. Put fresh teflon tape on threads
6. Screw expansion tank back on
7. open fill valve
8.pressurize system


is this about right? please let me know if I have left anything out. I am concerned I will try to do this, and not be able to get it all back together again before the evening. (wife would not be happy)

Thanks
 
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Old 01-27-07, 02:41 PM
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Lightbulb

There are a few reasons for the PRV leaking

The first is the PRV itself, but if it stops leaking when the pressure is at 12 psi and leaks at 30 psi, it's just doing its job.

The expansion tank will water log if the bladder develops a hole in it or if the air escapes through a bad valve core. When you drop the pressure in the boiler, if the tank is mounted with the threaded connection up, the tank will remain full of water and be very heavy (and come crashing down when you unscrew it) also if it's waterlogged you will get water from the air valve on the other end.
If the bladder has not leaked but the air is gone, when the boiler pressure is dropped to 0, the pressure at the tank's air valve will be at or close to 0.

Another reason would be that you fill valve is leaking past. The fill valve is designed to refill the boiler and to keep it at least 12 psi. If the valve is failing, it will let water into the system and overfill the boiler. To test this, shut the valve to the fill valve and see if the problem goes away.

As you stated, your domestic hot water coil can develop a leak, allowing domestic water to leak into the boiler, also causing it to be over filled. Test this by shutting the cold water supply valve to the domestic coil to see if the problem goes away.

Also, your expansion tank may be undersized. The ET15 is only good to 50,000 btu with baseboard heating, you might need a #30 (ET30)
check out this link:
http://www.watts.com/pdf/es-et.pdf
 
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Old 01-27-07, 03:21 PM
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There's a problem referring to the relief valve with the PRV acronym.

It can also refer to the Pressure Reducing Valve (aka fill valve).

I think it's best to just spell it out and forget the acronyms.

Like HVACGuy said, that tank will be MUCH heavier than you expect it to be if it is waterlogged! 15 gallons of water at 8 pounds per gallon, you do the math... best to have a helper at the ready, and ASSUME it is full of water when removing it.

Your steps are pretty much correct. But, before you take it off, test it. Momentarily push the schrader (tire) valve on the end of the tank and see if you get air or water.

If you get water, follow your steps and replace the tank.

If you get air, or nothing, re-pressurize the tank. You shouldn't need to remove it to do so, just put 12 PSI in with a tire pump or small air compressor.

If you do simply re-pressurize, monitor the system for the next week or so. Sometimes it will take a while to leak down and the problem will return.

HVACGuy, I don't think the fill valve is bad, cuz he sed it's at 12 when cold...
 
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Old 01-27-07, 06:43 PM
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Good point. I assumed it was drained back to 12 psi. Shoulda reread.
 
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Old 01-28-07, 06:32 AM
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Thumbs up expansion tank

Upgrading to a #30 tank would be good regaurdless. It is very easy to change, assuming the old one comes off easy enough. Be sure not to over tighten it when installing so you don't crack the air scoop, and be very liberal with the teflon tape ~ apply about 6-8 wraps in a clockwise direction from the threaded end. NJ trooper, the #15 has a capacity of about 2-3 gallons +/-, and the #30 has a capacity of 4-5 gallons +/-, and on a personal note, I'll do the pipng schematic this week for you, as I'm taking this week off and will be only doing emergency work, so I'll have more time. It's been a long couple of weeks!
 
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Old 01-28-07, 10:02 AM
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Originally Posted by HVAC-EMT
the #15 has a capacity of about 2-3 gallons +/-, and the #30 has a capacity of 4-5 gallons +/-, !
Isn't that just the normal "acceptance" capacity of the tank with an intact bladder and proper pressure on the air side ? Maybe not 15 gall, but if that bladder is shot I'm pretty sure there could be considerably more water in the tank. But yeah, yer right, I did overstate. In any case, plan accordingly!

Take yer time on the diagram, I'm still a few months away from the work.
Let that back heal!
 
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Old 01-28-07, 10:22 AM
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My first attempt is going to be to repressurize the current system, although after looking at the PDF of the ET-15 it does seem as though the ET-30 is the right size for my radiant heat system. My boiler has a rating of 105,000 BTU per hour. Just to clarify a couple of things: My domestic hot water heater is separate from the boiler, and the Expansion tank is mounted vertically with the schraeder valve at the top...

NJTrooper (or anyone else who may know), You mentioned that I wouldn't need to remove completely to repressurize the tank. I was under the impression (possibly wrong) that the pressure in the tank will reflect exactly what is reading on the pressure gauge for the system (as long as it is working correctly). So I guess my thought was if I bled the system down to zero, the expansion tank would also read 0. is that right? OR when the system is bled down with the expansion tank still connected, will it read 12PSI (under normal conditions), and that is why I wouldn't need to disconnect it. I had thought I had read that the only way to truly gauge the pressure was if it were disconnected. It would seem to me that if the system were at 12 or less than 12 in a fully functioning system, the expansion tank would always read 12, whereas as the pressure increased in the system the pressure reading on the tank would mirror that.

thoughts?
 

Last edited by chakangt; 01-28-07 at 10:37 AM.
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Old 01-28-07, 11:35 AM
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With the air valve on top of the tank, the "push it and see if water comes out" may or may not be a valid test. You MIGHT get water but you might not.

As you probably know there is a rubber diaphraghm inside that tank (think baloon in a can) that separates the air and the water. With ZERO pressure on the WATER side you should still have pressure on the AIR side. This is what's referred to as the "pre-charge".

When you start to pressurize the WATER side, you will still read the pre-charge pressure at the schrader UNTIL the system water pressure exceeds this. At that point, the tank begins to accept water from the system, and the "baloon" is compressed, and you will see the system pressure on the schrader.

As long as you have ZERO PSI on the water side of the baloon (bladder), you don't need to remove the tank in order to pressurize the air side. If the valve between the tank and the air scoop is open, (it should be) you should see the same pressure on your system pressure gauge as you put in the air, because you will also be pressurizing the system. To be most accurate, open a drain for a second to release the system pressure. Check the air side again with a tire gauge .

You actually want about 1 PSI LESS air in the tank than your system pressure WHEN THE SYSTEM IS COLD. This is because you still want that bladder to be just slightly pressed on (just a small bit of water in the tank) when the system is cold. If you have too much pressure on the air side, you will see drastic drop in system pressure when the system goes cold. In fact, you may even end up with a vacuum on the water side ! Not enough air in the tank, and the pressure will spike up when it gets hot. It's a balancing game.

I agree to just go ahead and replace it with the 30 if you find it's bad.
Just be sure and check the pressure on the air side before you install it. They are supposed to come pre-charged, but...
 
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Old 01-28-07, 06:12 PM
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So I have some good news and some bad news...

The good news is I depressurized the system and there was no pressure in the expansion tank. So I repressurized it to 12 PSI (actually closer to 11PSI). Then I filled the system and fired it up. Now for the bad news....

When the system got up to operating temperature (140 F) once again the needle was approaching 30 PSI and the Presssure Relief Valve was weeping.

So now I am waiting for the pressure to go down so I can check the pressure at the expansion tank again. If it is at 0 then I think we know what needs to be done. If it is still at 12PSI, what is the next thing I should look at. I would like to remind everyone that the Pressure Reducing Valve is rock solid at 12PSI. When I filled the system after depressurizing it, it filled back to 12 PSI on the button.

Thank you to everyone for their help in this... I look forward to hearing your suggestions about next course of action. I am starting to think it may be time to call in a professional, but would like to versed on what other causes there could be for the high pressure...
 
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Old 01-28-07, 09:17 PM
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chakangt - measure it tank off

Isolate and remove the tank. You'll be 100% accurate AND you won't lose but a splash of water. The alternative is draining down to zero PSI, and all that water has to be replaced.

That's my view and other people have different views. This is a very religious area of hydronics.
 
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Old 01-28-07, 09:19 PM
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Is the isolation valve between the x-tank and the system open? Silly things like this happen at times...
 
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Old 01-28-07, 10:45 PM
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Originally Posted by Who
Is the isolation valve between the x-tank and the system open? Silly things like this happen at times...
I'm sittin' here scratchin' me haid, wonderin' WTH is goin' on ?...

Then Who said that, and I said to myself... yeah, that's gotta be it.

chakangt, you did re-open that valve, right ?
 
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Old 01-29-07, 05:31 AM
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The valve to the x-tank is open (I know small details like that can slip by). When I depressurized the system I decided to leave it open so that the pressure on the water side would remain zero. was this potentially a mis-step? I am waiting this morning for the house to warm up before I drop the pressure in the system and check the pressure in the x-tank. What I am hoping to find is that it has dropped to zero again.

I don't know if this is a predictor... but when I went down to monitor the system the vertical line connecting the expansion tank to the system was hot (this is how I am sure the valve to the x-tank is open, along with checking the valve), but the tank sounds hollow when I tap on it. It seems as if there is only air in the tank and no water... not even at the bottom. is this completely unheard of? or maybe there actually is water in it, and when I tap on the top and bottom I am not hearing the difference...

Thanks again for everyone's suggestions...
 
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Old 01-29-07, 08:00 AM
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I'd remove the tank and pressurize it. Maybe leave it off for a few hours with a gauge attached and see how well it holds pressure.

If your pressure is increasing with water temp, it has to be a tank issue. Unless this is a new system, sizing shouldn't be an issue (although ET-15s are small for many systems).
 
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Old 01-29-07, 02:02 PM
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So, I have an update... The heating cycle this morning was just like the others... 18PSI at 100 degrees, and by 140 degrees it was showing just about 27 PSI. So I decided it was time to act.
I had pressurized the system last night to 12PSI with the tank still attached and pressure at 0.
I went downstairs after the system had cooled and depressurized the system. I took a reading on the xpansion tank and it was in the 10-12 range (crappy gauge). I then unscrewed the tank from the system. It was dry as a bone and still pressurized. when peering into the hole in the tank i could see the bladder pressed up against the hole.

So, while the tank was off, I did a little fishing with a coat hanger to see if there was an obstruction. I was able to feed the coathanger down cleanly all the way to the shut off valve but no further (my tank sits at the top of approximately 36" of 1/2 pipe which I imagine sits atop the air scoop? although I don't think i have an air scoop.) I am not sure if there is something at the base below the shut off valve or not.

So everything seemed clean an unobstructed... Now I have reinstalled the tank and am seeing what is going to happen (either get a leak because it isn't screwed in tight enough or get high PSI again...)

so I guess my thought would be is it possible there is an obstruction in the rest of the system? everything seems to move fairly well... all radiators get hot, and temperature rises at a steady pace...

so off to check for leaks...
 
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Old 01-30-07, 08:23 PM
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So,
I had the pros come in and take a look at things. we replaced the et-15 with an ET-30 as the documentation from Watt's (and people on this forum) suggested that the #15 tank was undersized.

So now, it has helped a little. the pressure isn't getting as high as quickly, but it is still rising past 20PSI when it hits 130 Degrees. Then as the temperature increases the pressure increases as well (up to 27-28psi at 150-160). The pro that I had in was confident the problem is solved because he said it was a cold day, and normally I wouldn't be running the system so much (in order to test we had the system run for 40 minutes). I, however, am not. I don't think I should be seeing pressures above 22psi. am I being over-concerned?

The #30 tank helped, but I don't think it totally got rid of the problem. I verified the circulator is working and that all valves are open and that the Pressure reducing valve is not faulty.

Thank you for all your advice... please let me know if you can think of anything else i can look at, and also what I should say to the plumber.
 
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Old 01-30-07, 08:36 PM
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Do you still have the original expansion tank? If so then plumb it in along with the new (larger tank. Your symptoms are classic of an undersized expansion tank. The tank MUST be sized according to the total amount of water contained in your system and the maximum range of temperature, not according to the BTU size of the boiler. The maximum range of temperature is figured from the coldest ambient temperature of the system to the highest possible temperature of the system.
 
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Old 01-30-07, 09:54 PM
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I wouldn't worry about 20-22#s... Glad to hear this is resolved.
 
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Old 02-01-07, 05:07 PM
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20-22, no I wouldn't worry either, but the pressure is up to almost 28 ! That's too high...

Did your "pro" check the pre-charge on the new tank, and set it 1 PSI lower than the normal cold system pressure ? Maybe there is too much air in the tank. Have you EVER bought new tires and NOT had to let 10 PSI out when you got home ?

Let the pressure out of the system and check the pre-charge.
 
 

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