"Bubbling" sound in HW boiler

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  #1  
Old 02-17-09, 11:59 AM
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"Bubbling" sound in HW boiler

During a recent bitter cold spell, I heard strange noises in the HW baseboards. I traced it to a bubbling that seemed to come from the boiler. Never heard that in the 25 yrs. we had the new house. This occurred several times over 2-3 days, but has not occurred since then. I found that the temp. gauge read between 180 - 190 during a normal burn cycle( burn=3-5 min.). Did not see what temp. was when bubbling was heard. Boiler gauge reads 17 psi when hot. The Amtrol Mod. 30 tank has never been bled, but seems filled with air at 16 psi( good dial type gauge). Exp tank rings hollow at the bottom and very top. Sound "dull" on the sides in the top half - I think the bladder is pressed against the tank sides. No water came out when checking air pressure. The tank is at the end of a stub line coming from a tap in the Peerless HW-110 boiler. That is also where the "float" type air release valve (Amtrol # 700 ??) is located.

System was flushed once about 15-20+ years ago.

I think all the above indicates normal operation. Right?

Since it seems to be working now, I won't "break" it by trying to "fix" it now. I will wait for warmer weather, unless it acts up.

What is likely to be going on? What should I do?
How long should the cast iron boiler last? Is it corroding inside and causing localized hot spots that "boil" when the temp. says 190? Can the Aquastat have a contaminated contact to the temp tap well? Can I remove the 'stat' with power off and without draining the boiler?

From what I've read on the internet, this site seems the most knowledgeable.

I've read that the boiler should only be filled half full. Is that right?

I've also read that the water should be heated well past boiling but the press. keeps it from doing so. 180-190 is not "well past" boiling. What's up?
 
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Old 02-17-09, 12:43 PM
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Originally Posted by bigedw323 View Post
I've read that the boiler should only be filled half full. Is that right?

I've also read that the water should be heated well past boiling but the press. keeps it from doing so. 180-190 is not "well past" boiling. What's up?
You said that you have a hot-water system, not steam. So neither of those suggestions is correct.

A hot-water system has to be completely full of water, except for a conventional expansion tank.

If you are getting localized boiling at hot spots in the boiler (might sound like popping or rumbling), try reducing the temp a little. 190 deg on the top end is pretty high.
Doug
 
  #3  
Old 02-17-09, 01:11 PM
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The Amtrol Mod. 30 tank has never been bled...
Diaphragm tanks (like yours) never have to be "bled".

...seems filled with air at 16 psi...
You cannot ascertain the pressure in the bladder while there is pressure in the system, all you will do is measure the higher of the two pressures.

Exp tank rings hollow at the bottom and very top. Sound "dull" on the sides in the top half...
Temperature and sounds are meaningless when trying to ascertain the condition of a diaphragm expansion tank.

No water came out when checking air pressure.
This is good.

The tank is at the end of a stub line coming from a tap in the Peerless HW-110 boiler. That is also where the "float" type air release valve (Amtrol # 700 ??) is located.
Picture would be helpful.

System was flushed once about 15-20+ years ago.
Flushing is only necessary when the system is first installed. After that the less "new" water added the better.
I think all the above indicates normal operation. Right?
With the exception to the bubbling noise you are correct.

How long should the cast iron boiler last?
Theoretically, forever. In practice, with a "tight" system (no leaks) at least fifty years. If you are continually adding new water it could rust out in five years or less. Also, some boilers use "O" ring seals between the sections, these have proven to be a source of problems. Some cast iron sectional boilers really prefer to be kept hot at all times while others can take long periods of nopt being fired with no problems.

Is it corroding inside and causing localized hot spots that "boil" when the temp. says 190?
Possible, but doubtful if you are not constantly adding water. If the initial fill of water was extremely hard this could be a possibility.

Can the Aquastat have a contaminated contact to the temp tap well?
Sorry, I do not understand this question.

Can I remove the 'stat' with power off and without draining the boiler?
Most likely, yes. A very few aquastats have direct immersion bulbs that would require at the very least that the pressure in the boiler be dropped to zero. If the "capillary tube" (thin copper tube) goes into a hollow well then you may remove the bulb by gently pulling on the tube. If the capillary tube goes into a larger, sealed tube and that second tube goes into a sealed fitting on the boiler you may not remove the bulb without dropping the pressure.

I've read that the boiler should only be filled half full. Is that right?
If this a hot water (not steam) system then that statement is absolutely false. Hot water systems MUST be completely filled.

I've also read that the water should be heated well past boiling but the press. keeps it from doing so.
The boiling point of pure water at "standard" conditions (sea level with the barometer at 29.92 inches of mercury) is 212 degrees Fahrenheit. The "design" temperature of almost all residential non-radiant systems is 180 degrees F. At a pressure of 15 psi the water must be at approximately 250 degrees F. before it will boil. To my knowledge no residential system operates at higher than 240 degrees F. and anything above the previously stated 180 degrees F. is rare. Some commercial and industrial systems, known as "High Temperature Hot Water" will operate at higher temperatures. I used to work in such a plant and the design parameters were 315 degrees F. at 150 psi max.


Your "bubbling" noise is indicative of low water but the pressure and temperature readings are completely normal. You may want to take several pictures of the boiler and piping to allow myself and the others to see if anything on your system looks abnormal. 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.
 
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Old 02-18-09, 12:40 PM
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Here are pix of my heater:

http://i705.photobucket.com/albums/w...sinReturn1.jpg
http://i705.photobucket.com/albums/w...esinReturn.jpg
http://i705.photobucket.com/albums/w.../ZoneValve.jpg
http://i705.photobucket.com/albums/w...sRegulator.jpg
http://i705.photobucket.com/albums/w...er/Overall.jpg
http://i705.photobucket.com/albums/w...ssWeeping2.jpg
http://i705.photobucket.com/albums/w...ntakeValve.jpg
http://i705.photobucket.com/albums/w...t_ExpTank1.jpg

The pressure relief valve is weeping slightly and probably has been, although I just noticed it. The dark spot is water and there are a couple of fresh looking drops on the end of the pipe. Note that the end is corroded away. As mentioned before, the temp. varies from 180 to 190 during a heating cycle.

Is the 10 deg. difference right?

Prior to my post, I did reduce the setpoint slightly on the Aquastat (HW L8148E) temp regulator dial, as gilmorrie suggested. It's now at 180. while before it was about 190. However, the hi/lo temps did not seem to change much - still the 190/180 as before. Why no change?

Since I have seen no movement at all on the pressure part of the boiler gauge (Perhaps it is "frozen"), I am making an adapter to check the actual pressure in the boiler.

Should you see a pressure change during the 180-190 temp change or do you have to drop the boiler temp to 100deg.? How much should it change typically? FYI - I have a two story colonial w 2 zones 28' x 38' each floor.

furd - I've read that bladder tanks lose air over time. Isn't it likely that my tank is "undercharged" with air and it should be charged?

Please explain why the "bubbling" is symptomatic of low water.

Is it really boiling inside or is the sound from something else?

We do have very hard water. I just had the 6th water heater installed since we got the house new in 1984.

With the "weeping" relief valve and hard water, is sediment and corrosion a likely culprit?

PS - I'm currently unemployed, 'nuf said.
 
  #5  
Old 02-18-09, 02:34 PM
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I've read that bladder tanks lose air over time. Isn't it likely that my tank is "undercharged" with air and it should be charged?
Yeah, I've also read that but the only residential system I worked on (installed in 1973) never lost any air from the bladder tank up until the middle 1990s when I last checked. I sold the house after my mother died in '97. On the other hand, I took care of several commercial sized systems during my working career and they all lost bladder pressure to the point of needing a shot at least once a year. Maybe the expansion tanks from 1973 were just really, really good.

At any rate, you need to drop the boiler pressure to zero in order to test the air pressure on the bladder. If you don't you will be reading the higher of the two pressures; system or bladder.

Please explain why the "bubbling" is symptomatic of low water.
I had misread your original post when I when I wrote that, I thought you were hearing bubbling in the baseboard units and/or connecting piping. If you are hearing what might also be described as mini explosions from the waterside of your boiler then it could very well be localized hot spots caused by excessive scale in the boiler. What happens is that the scale insulates the boiler metal from the "cooling" of the water and any water trapped under the scale does indeed turn to steam and the result is a mini steam explosion that pops the scale loose. With your poor quality water that is a distinct possibility. Unfortunately, de-scaling a cast iron boiler is usually an exercise in futility. You might be able to get a few more years service if you can remove all the "boiler mountings" (valves, gauges and fittings) and try to wash out as much crap and corruption (those are technical terms ) as possible. It will make one heck of a mess and you will probably want a helper manning a wet vac to keep the mess from getting too bad.

The real fix is to replace the boiler, I know that isn't possible at this time and I hope that you are able to get back to work soon. I do suggest that you replace the safety valve and when you do, install an elbow so that the stem of the safety valve is in the vertical position. Safety valves should always be installed with the stem vertical and they should be replaced every five years as a matter of preventive maintenance.

I also suggest that you replace the pressure gauge as it is likely not reading correctly. I think what I would do is leave the present pressure gauge/thermometer in place and remove the expansion tank. Install a tee immediately below the elbow and install a generic pressure gauge in the side of the elbow. Below this new tee install a ball valve and then another tee with the expansion tank installed into the bottom of this last tee. Install either another ball valve (preferred) or a plug in the side of this second tee and you now have a method of isolating the expansion tank from the system to allow you to easily check the bladder pressure or, if necessary, change the tank without having to shut down the entire system. Trooper has a diagram of this arrangement and maybe he will post it in this thread. You will also want to fabricate a hanger to support the weight of all this from something more than just the long horizontal nipple now in place.

As for the temperature settings, I'm going to leave that to Trooper as he has more recent (and better) experience than I.
 
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Old 02-18-09, 06:27 PM
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Uh-o, I am now getting dangerous. I've been reading and now I think that the boiler manufacturer (Peerless) has engineered the boiler to not "pump away" from the “the point of no pressure change”. The circulator pump is inside the case in the return side. Thus, it pumps water into the boiler (& the “the point of no pressure change”. That point is a tap in the center top of the boiler.

Is my analysis correct?

How important is "pumping away"?

What are the practical consequences of not "pumping away"?

Is it a relatively new idea, not prevalent in 1984?
 
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Old 02-18-09, 08:35 PM
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I would venture to say that probably 75% (or more) of residential systems are not "pumping away" from the point of no pressure change and they work just fine. The idea of pumping away is not new. I suspect the reason that it isn't (or hasn't been) piped that way more often is primarily because boiler manufacturers often bolt the pump onto the return side of the boiler for shipping purposes and they just don't get moved to the proper place when the system is installed. Another reason is that often installers have learned their trade via on the job training and do not understand the physics of pumping away. Often this is stated as, "This is the way I've been doing it for fifty years and I'm not changing now." It's sad, but true that most people are resistant to change unless someone shows them why the change is better than the old way. It's not that the "old timers" are stupid, just that they don't understand why pumping away is better.

My entrance to this board came about from reading a long thread about air problems in one of the member's system. I was not the first to point out the concept of pumping away but the earlier posts on the subject were not truly taken as meaningful because so few people understood the physics behind it. Even when the member who was having all the trouble understood the physics he thought it would require a massive repiping of his system. When I pointed out a simple means of achieving pumping away (move the expansion tank connection to the pump inlet) he tried it and finally his air problems were over. He became a convert to pumping away and is now one of the regulars here that offer excellent advise on circulator pumps and air removal.

In the real world his problem was one that rarely crops up and as I stated, most systems work just fine with the pump on the return and the expansion tank on the discharge side of the circulator. I rather doubt that changing your pump's location or the connection point of your expansion tank will make any significant difference in how your system operates.
 
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Old 02-19-09, 10:55 AM
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Have to confess that I didn't read the whole thread... been down with flu for a few days... but wanted to post this diagram as I think it's the one that furd was referring to in his reply.

I don't even want to tell you guyz the date code on my expansion tank! But, it does lose a few PSI/year... I think the older ones were MUCH less disposable than the new ones!



As for the temperature settings...
180 should be fine for the high setting. You won't see much pressure change between 180 and 190 ... how much pressure change you see is ultimately dependent on the size of the expansion tank relative to the water volume in the system and the DIFFERENCE in temperature...

USUALLY, I might expect to see at least a 3-5 PSI change from cool to hot boiler... but I would not be uncomfortable with 10 PSI, as long as I knew the air charge in the tank was correct, and the HOT pressure was still 25 or less.

furd also mentioned something like this... which I would not do with copper... but black pipe for strength...

 

Last edited by NJT; 02-19-09 at 11:11 AM.
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Old 02-19-09, 01:29 PM
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Furd,

Thanks for your info.

I just independently verified that the boiler pressure is 15 psi. So, maybe my old gauge is OK after all. It seems that the bubbling is likely to be from the mini- explosions you mentioned.

Can they be self- correcting? i.e. once the "crud"(technical term ) is blown off, the bubbling will go away? They have not happened again in the last 2-3 weeks.

Are these something to worry about if I do nothing? I'm not about to disassemble the boiler.

In my situation - very hard water, leaking relief valve(approx. 1 oz. per day), open supply valve (adding water) - is it likely a simple flushing will do much good?

What is best way to flush? Let boiler cool down (later in the spring), open supply valve and pressure relief and let 'er go, or some other method?

Why should the relief valve stem be vertical? Keeps seat cleaner??
 
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Old 02-19-09, 03:50 PM
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Thanks, Trooper. Yes, that's the diagram and I also like the picture. I agree that it should be black steel pipe rather than copper but I don't like copper on the boiler anyway.

Bigedw, your pressure gauge may be okay or it may only be good at 15 psi. I can't tell you how to spend what precious little money you have but understand that the conditions under which that gauge has been living are far from ideal.

I can't say that your boiler will be "okay" with the scale being blown off from the steam explosions nor can I give you any kind of magic fix that will make it any better. The truth is that your boiler is running on borrowed time. It may last another five years and it might start leaking tomorrow, I simply can't make any prediction.

You do need to replace that leaking safety valve, that is a must. You can almost certainly wait until warmer weather when the heat will not be needed to do any work, UNLESS something really bad happens. I am a firm believer in working on boilers in the summer and working on chillers (air conditioning systems) in the winter. Unfortunately far too many people forget all about their boiler once the heat is no longer needed and don't remember until the weatherman forecasts a cold snap.

The safety valve should be piped with the stem vertical because that's the way the valve is meant to be installed by the manufacturer. It probably doesn't make a whole lot of difference with the seat but it can make quite a difference with the spring chamber in the body above the seat. The body has a drain hole to allow any water in the spring chamber to drain away immediately. If water remains in the spring chamber it can corrode the spring and/or part of the valve disc attachment. Under a worst-case scenario this could render the valve inoperative. My personal feeling is that the safety valve should be hand-lifted (tested) at least once a year. In commercial and industrial work the safety valves on larger boilers are removed and sent to an authorized repair station for testing and repair every three to five years. This, of course, is not economically practical with these small safety valves so insurance company recommendations are to simply replace them every five years and I agree with that schedule. Remember that a non-functioning safety valve is no better than a pipe plug.

I don't think trying to drain your boiler and refilling via the make-up water system would do a bit of good in removing the scale, crap and corruption and would likely just plug up the drain valve. You really would need to remove the drain valve, and if it is threaded into a reducing bushing, then remove the bushing also to get the crap out. You need a good flow of water to wash anything out so if you don't remove at least some pipe (the safety valve opening would be better than nothing) and direct a good flow of water through the boiler you might as well do nothing.

If you have a water softener in your home the make-up water should be from the softened water system. Don't change it now as the damage has already been done but when/if you get a new boiler have it piped correctly.
 
  #11  
Old 02-23-09, 11:58 AM
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Thank you guys both for all your help.
 
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Old 02-23-09, 06:26 PM
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Just reading these posts and I have to tell you You guys are a wealth of information
Thanks for the info
 
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