Weil Mclain relief valve "exploded" open

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  #1  
Old 10-16-09, 04:41 PM
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Weil Mclain relief valve "exploded" open

I added water to my Weil McLain CGM boiler to bring the pressure from 10 to 15. about 1 hour after the heat went on I heard a "boom!" The pressure relief valve had burst open spraying water and sediment all over the walls, floor and ceiling.

I shut off the boiler and I put a bucket under the relief valve pipe and it slowly filled with about 1.25 gallons of clean water, then stopped.

Do you think it is OK to continue to operate the boiler? It seems the relief valve must have gotten blocked with sediment and the pressure caused a water explosion. Is there a way to check if it is still OK to use?

Was the problem that I added about 1 gallon cold water to an already warm/hot boiler?

It was a terrifying experience.
 
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Old 10-16-09, 05:03 PM
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I imagine you had to change your undergarments after that!

Here's what I think happened...

Your EXPANSION TANK is probably in need of service, meaning that if it's the older type, steel, strapped into the joists above the boiler, it is nearly 'waterlogged'. If it's the more modern type that looks like a propane tank from a gas grill, the air charge may be low.

This will cause the pressure in your boiler to rise above the relief valve setting.

Your relief valve probably has never seen an opening, and the valve seat had 'glued' itself shut... stuck.

The pressure increased until it literally BLEW open...

What I would do.

Check/verify/service the expansion tank.

Replace the pressure relief valve.

Check/verify/service the automatic water fill valve if so equipped.

If you call a service person, these are the things they should do.

You may be able to perform some of this yourself, if you are so inclined... let us know.

You may be able to operate safely by reducing the pressure a bit, and closing the water feed valve, but you would want to keep an eye on the pressure gauge if you did this, and only do as long as possible until you can get it fixed... soon.
 
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Old 10-16-09, 05:05 PM
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Trooper beat me to the punch line.

I also agree with everything that he wrote.

If you want to DIY this then a good place to start would be some pictures of your installation. To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected.
 
  #4  
Old 10-16-09, 06:20 PM
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relief valve exploded open

Thanks for the info! The "boom" happened two floors below me. I just saw the aftermath.

We did empty the expansion tank a couple hours before the relief valve blew. (drum type - strapped to joists). There was only a few drops of water in it. Also just checked expansion tank again now - just a few drops of water. Maybe the line to the expansion tank is blocked too? Or by "draining" the old type of expansion tank did too much air get in? - the valve handle to it, is always open except when we add water.

The relief valve pipe used to occasionally dribble water a few years ago, (unfortunately I didn't know this was a problem). It stopped a couple years ago and it must have become coated with sediment.

The pressure is way down at 2 or 3 psi now. Maybe the pressure gauge is off or broken? The boiler is cold now. Does the relief valve have to be replaced? Is there a way to check to see if it is still OK? Or are you thinking it has been damaged. (can it be tested when the boiler is cold with only 2 psi)

I only have a manual water feed line. We always keep it off, unless we are adding some water (about once every couple years). The on/off handle is between the boiler and the backflow pipe.

If you want more info I will take and upload photos. Thanks so much!
 
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Old 10-16-09, 06:43 PM
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Yes, you need to replace the safety valve. It should be replaced every five years under the best conditions.

It is certainly possible the piping to the expansion tank is plugged. It is also possible that the expansion tank is full of water and the drain is plugged with solids. Or, that you have not been allowing air to enter the expansion tank when you think it has been drained.

If it were my system I would get rid of the old expansion tank and install a bladder-type expansion tank and also a pressure reducing (automatic make-up) water valve.
 
  #6  
Old 10-17-09, 05:33 PM
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Expansion Tank

I'll bet dollars to donuts the tank is full not empty. To drain a conventional tank, air has to go in so the water can come out.
 
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Old 10-20-09, 09:01 AM
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To drain ex tank

Tank holds about 20 Gal of water when full
*hint* for systom to work right, tank must be empty. Taking only 5 gal of water out, the tank is still under vacuum, meaning that when you open valve at other side of tank water will be sucked in to tank making it full agan*

* things you need: 4 ft of hose, 6 gal buckett *
* Hint: at 8.3 lbs to gal of water it's Heavy. Also you don't want to spill it as you carry it to empty it. ( you don't want to spill it over the white carpet ) been there done that.

1 close valve going to tank
2 attach 4 ft of hose to drain valve at other side of tank
3 open drain valve. You will get about 5 drops of water out of it
4 take end of hose and BLOW in to it. It will be hard doing it but it will be easy after you get more water out.
*HINT YOU HAVE TO BE FAST OTHER WISE YOU WILL GET A MOUTH FULL OF WATER *
5 you will know the tank is empty when you blow in to it and you get just air out of it.
6 close drain valve, tuck hose under brackets that hold tank.
7 open valve on other side of tank. You will hear water running into tank. It will also be warm. thats ok
8 check pressure gauge on boiler. It should be about 12 lbs, you're done.
William
 

Last edited by NJT; 10-20-09 at 02:57 PM.
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Old 10-20-09, 03:02 PM
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Expanding on what William said a bit... if you do resort to blowing into the end of the hose, BE CAREFUL! As he said, you can get a face full of nasty stanky boiler water! If you have a small air compressor, you may be able to use that instead of your mouth.

If you use a short hose as recommended, the job will be easier, because the hose won't fill with water and will often allow some air into the tank.

Sometimes leaving the hose end at the drain valve a little loose will let it suck the air in also...

Think of the drinking straw... when you put your finger over the end of it and lift it out of the drink, the liquid stays in the straw. The same thing happens to your tank. You get a bit of water out and the flow stops, you think the tank is empty, but it's not... So you have to sometimes force air into the tank to break the 'suction' or 'vacuum' in the tank.
 
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Old 10-20-09, 03:39 PM
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Could you post photos of the exp tank and the connections to it? The reason I ask is: if it has a B&G airtrol tank fitting, all this huffing and puffing might be avoided. An airtrol tank fitting has a tube that leads up into the tank, above where the water level needs to be.

If there is sort of an ell-shaped, cast-iron, red fitting on the bottom connection of the tank, then that's a B&G airtrol tank fitting.
 
  #10  
Old 10-20-09, 05:37 PM
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Thank you: "Empty Expansion Tank, Pressure Relief Leaking"

Thank you everyone who posted ideas, but it was the "Empty Expansion Tank, Pressure Relief Leaking" detailed info that really helped me understand my problem.

I had the exact same problem as that person! (except I don't have the additional leaky water feed valve problem fortunately). It was all the detailed descriptions of the water being "reluctant" to exit the expansion tank and then acting like an "office water cooler" and "straw" that really helped.

We replaced the safely relief valve last night (Good thing we replaced the safety valve - not too difficult, it was pretty corroded inside.) Didn't fire-up the boiler until this morning. The cold pressure was at 10psi. I turned on the boiler and after 1/2 hour checked - it was at 20psi, checked again at 1 hour and it was at 32 psi with the new relief valve expelling a small stream of water. I shut off the boiler and got scared (knowing over 30psi is very bad). I bleed 2 cups of water out of the upstairs radiators, the pressure went back to lower 20's.

Then I spent 2 or 3 hours reading forums and came across "Empty Expansion Tank, Pressure Relief Leaking". This was exactly my problem!

After the boiler cooled down, my husband and I decided to try opening the expansion tank again. Knowing to expect a few drips before the draining got underway, we waiting through the drips and after a couple seconds, YES, more water came out! (I forgot to close "valve C" from tank to boiler for the first minute. Noticed it was opened and quick shut it, this might have helped create a suction to help draw out the water from the tank)

It took 45 minutes of water-cooler type draining/burping, AND 15 - 20 gallons later, I now have an empty expansion tank! The water also got dirtier as more came out.

After that the cold pressure was back to 6. I added water and brought it to 8 - I was too afraid to bring it to 10 right away (I don't think there is a water-pressure reducing thing on the feed valve).

I turned on the boiler and let it heat the house from 66 to 72. I sat and watched the pressure gauge for 1 hour and then checked it again a half hour later when it just turned off.

Results:
Beginning temp: 50, pressure 8 psi, expansion pipe cool.
After 1/2 hour: temp 105, pressure 9 psi, expansion pipe is warm, tank is cool.
After 1 hour: temp 140, pressure 10 psi, expansion pipe is hot, tank is warm.
After 1 1/2 hour: temp 130, pressure 9 psi (boiler had been off 1/2 hour) expansion pipe cool again.

Previously I had checked the expansion pipe and it had always been cool. This is my first time trouble shooting boiler problems, and I didn't think to ask before if the tank pipe should be warm/hot when the boiler is running.

I think my problem has been solved. I'm so happy to see the boiler pressure isn't dramatically rising with the boiler temp anymore!

Since I had to add quite a bit of water to bring the pressure just to 8 psi, do I have to worry about excess oxygen?

Do I appear to be in the clear now?

Thanks TONS for everyone's input. This thread and the "Empty Expansion Tank, Pressure Relief Leaking" have been invaluable and have saved me at least $200+

Thank you!!!!
 
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Old 10-20-09, 06:25 PM
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You really do want to bring up the cold pressure a bit higher though... the slightly higher pressure will make those pesky air bubbles out in the system a bit smaller, and easier to move back to the boiler, where hopefully they end up in the expansion tank where they belong.

I would go for 12 PSI cold...

That seems like an awful long time for the boiler to run to bring up the temp that small amount though...

What kind of radiators do you have again? (I know you probly told us, but I'm too lazy to read back, sorry!)

The reason the pipe to the tank got hot is because now there is room in the tank for the expanding water!
 
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Old 10-20-09, 06:47 PM
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I have regular, freestanding, rectangle radiators from the 1920s. House was built in 1924.

Yes, I will bring the water pressure up to 12 psi. I just wanted to make sure the "pressure problem" was under control first before adding too much water.

Thanks for the info, that adding more water will help take out the air bubbles.

Maybe the low water pressure meant it took longer for the water to circulate and get hot?

I think two of my radiators had been acting as expansion tanks in the past. My brother helped us install the safety valve yesterday and then he had us bleed all the radiators with the boiler cold. I had always done it with it hot in the past. Since yesterday, those two radiators have only "clanked" once.

So much stuff the average person doesn't know....

Thanks again for all your help!!!
 
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Old 10-20-09, 07:52 PM
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I have regular, freestanding, rectangle radiators from the 1920s. House was built in 1924.
This means that you have a large volume of water to heat up, and the amount of time is to be expected... there's a caution that should be mentioned to this... and we mention this a lot around here... the caution is FLUE GAS CONDENSATION.

Large volume water systems are particularly prone to this and there is a piping method of adding a 'bypass' valve to the system that allows the boiler to run up to temperature and prevent any problems from FGC... you see, that condensate is acidic and will eat away at the metals in the boiler and flue pipe. You may already have a bypass...

There's good reading here:

Bypass_Piping_Explaination

on the subject.

Bleeding hot or cold in your case will achieve pretty much the same result. Very good observation about the air filled rads acting as expansion tanks, because that can easily happen! Different setups call for different methods of bleeding, so do whatever you find works best for you!
 
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Old 10-21-09, 11:35 AM
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Thanks NJ Trooper,

I just posted photos of the whole system on photobucket. Pictures by silaurie - Photobucket

I have a couple questions. With a cold boiler, I brought my pressure up to 11 psi. It took about 10 minutes with the water feed open, to bring it from 9 to 11 psi. Is that normal?

Also I did an experiment. After bringing it to 11. I shut the valve to the expansion tank and emptied the expansion tank again. About 4 gallons of water came out (no burping water, water just poured out like a faucet, only burped at the end). Then I opened the expansion tank valve and I could hear some cold water going up to the tank and the pressure dropped from 11 to 6 psi. Is this normal for the expansion tank to have a few gallons of cold water pushed into it from the boiler?

If this is normal, is my next step, (of course with the expansion tank valve open-and kept open) to add more water until 12 psi? Turn on the boiler and heat the house? While heating, I want to monitor the gauge again to make sure the psi doesn't fluctuate too much. If that's all OK that problem should be solved, right?

Then should I just leave the expansion tank and let it do its thing for the season? How often should it be drained, or should it be partially drained? Once a year or every two years?

Now about the flue gas condensation: Can you see on my photos if there is bypass valve?

The last time we had the boiler inspected (7 years ago) the service man mentioned we should set the heat and leave it at a constant setting, like 68 and never change it to prevent the boiler water from condensing. We tired that and the problem with that was, 1. we had a big heating bill and felt guilty heating the house during the weekday and 2. Our upstairs is much warmer than the downstairs and it was hard to sleep at night, it was pretty warm. Do some people do this do prevent the FGC? We actually only want to be in this house another year or two, so I don't want to make any expensive changes. Also most of the pipes to the radiators are wrapped in asbestos, The home inspector said this was fine as long as they are sealed with tape and paint (which they are).

thanks again for all your help!
 
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Old 10-21-09, 04:58 PM
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It took about 10 minutes with the water feed open, to bring it from 9 to 11 psi. Is that normal?
No, not at all... IF you had a 'pressure reducing valve' though, it could be perfectly normal. Follow the water line all the way back to where it branches off the main house water... see if you see something that looks like this:


photo courtesy pexsupply.com

It could be red, green, etc, depending on manf, but basically the same shape.

I ask this because in the last photo, above the water heater, there is what looks to be another valve on the water line.

Is this normal for the expansion tank to have a few gallons of cold water pushed into it from the boiler?
Yes, perfectly normal. Since air is compressible, when you start with a tank full of air at atmospheric pressure, and then pressurize it to 12 PSI, the VOLUME (or SIZE) of the air is decreased. This is exactly what it is supposed to do, and what controls the pressure increase when you heat the water. The water when heated EXPANDS, and the the trapped air in the tank COMPRESSES, and the pressure in the system is controlled.

Then should I just leave the expansion tank and let it do its thing for the season?
Yes.

How often should it be drained, or should it be partially drained? Once a year or every two years?
As often as needed. On some systems that are really designed well, this could be as often as NEVER. What you want to do is due diligence, by keeping your eye on the pressure. Know what the pressure is when cold, and again when hot. If you see the hot pressure begin to climb out of control, you know it's time to drain the tank.

Can you see on my photos if there is bypass valve?
I do not see one.

The last time we had the boiler inspected (7 years ago) the service man mentioned we should set the heat and leave it at a constant setting, like 68 and never change it to prevent the boiler water from condensing.
The reason that was recommended was so that the boiler did not have to spend large periods of time bringing the boiler water back UP to temperature. The LESS TIME that the boiler spends with low return water temperature, the better. By maintaining the water temperature, the presumption is that you will spend less time in the condensing range, i.e. with boiler water less than say 135 returning to the boiler.

But, as you say, if it means sky high bills... well... choices to be made.

Seven years is a while to go between servicing... the main thing with gas boilers, is that the rust from the cast iron boiler block can flake off and block the flue passes, and fall on top of the burners. These rust flakes are a particular problem if there is FGC occuring. If it's a steel boiler (I don't think it is) not as much of a problem with that, but still...

Please say that you have functioning CO detectors in the home!

If there is partial blockage of the flue passes from rust, etc, and flakes of rust sitting on the burners, you do run the risk of exhaust 'spillage' into the home.

The 'upside' to all this is that if your boiler were condensing badly, I would expect to see rusty stains running down the flue pipe from the joints, and I don't see that. It doesn't mean that your system is NOT condensing, just that there are no outwardly visible signs that it is.

It has lasted this long without a bypass... and might do so for another 1-2 years... or maybe another 30 ... who knows?

By the way, it's not the boiler WATER that condenses... that's already water... it's the VAPOR in the EXHAUST, the FLUE GAS that will condense on cool surfaces, the same way that DEW forms on the grass. The MOISTURE, HUMIDITY, actually forms a 'dew' on the inner surfaces of the boiler, flue pipe, and chimney.
 
  #16  
Old 10-21-09, 06:11 PM
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For the slow fill of the system:

The feed valve being on an iron pipe can/will cause this. What happens is that on the cold water supply side the pipe rusts internally. And being a vertical pipe the rust falls and builds up against the valve.

The boiler here had the same issue. It would literally take hours to add a psi or two of pressure to the system. This past Summer I replaced the iron cold water feed with copper and a new valve. Fills right quick now.

Being that you won't be in the house much longer I wouldn't worry about it.

Al.
 
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