Simple flush of Radiator system .. now "Kettling?" and...

Baggins

Good Morning,







A little background on the system



1) pretty old .. originally coal, then fuel oil, now natural gas .. efficiency of flame probably not the best







2) Two story system -- 5 radiators on the first floor, 4 on the second

floor, expansion tank in the walk up attic with a 5 gallon bucket

hooked  to the overflow :o)







3) straight gravity system  with 2 sets of approx 3" returns and feeds

with approx 1 1/2" lines feeding and returning each radiator. All feeds

are wrapped in encapsulated asbestos







Ok so over the last year I considered replacing the boiler, thinking

that a little more efficiency wouldn't be a bad thing, but after a

couple of quotes I realized I could tolerate some inefficiency a little

while longer.







So I decided the system needed a little TLC since we were going to be

together awhile longer .. did a simple flush .. drained system (original

discharged water very black and a fair amount sludge) kept refilling

and draining until water was clean... took several times.







Vacuumed out the heat exchanger (lots of rust flakes)..







over the next few weeks bled and re-bled the radiators for air







Now I have 2 problems:







1) I have what I believe is called kettling.. only happens when system

is hot and heating .. stops shortly after flame kicks off .. sounds like

oxygen snapping through the scale







2) this one really has me concerned .. If I open the heat exchanger (top

door) the faces of the exchanger appear damp.. and when I am at full

fire and open it, it is still damp where it exits to the flue. So I am

wondering if I am really kettling or could it be that my Heat Exchanger

under full heat is expanding and leaching micro air leaks into the

system (not bleeding does not produce much if any air)







Thoughts or ideas to solve?







Thanks



Dan

Mark Eatherton

Bad news...

You'd best start rearranging the deck furniture... She's going down :-(



Kettling indicates boiling. Boiling, when not designed for it, can be very stressful on the heat exchanger. Kettling indicates a continuous fresh water make up leak within the system that introduces excess minerals, and thee minerals precipitate out on heat surfaces, and act as insulation to the heat transfer process. As the energy gets held back by this insulation, it eventually builds up to the point of JUMPING into the water, which occurs with a steam flash, and that is the kettling you are hearing.



Kettling MAY be addresses with an acid flush, but it may also cause the heat exchanger to fail completely, with no option but replacement. Sometimes, small cracks can be filled with lime scale. When you remove this lime scale, suddenly, there is nothing to hold the water back, and you will have water accumulating at the base of the boiler.



The accumulation of moisture in the fire box may not necessarily indicate a breach of the heat exchange area, in fact the heat exchanger is more likely to leak water when cold, rather than hot. If the system is operated with a return temperature below 140 degrees F, which is quite common for systems of this design, then what you are seeing is condensation, which is still not good. It has a pH of around 4 and it will eat cast iron.



Converting to a new system will produce a minimum reduction of around 30%, possibly more in your case due to inherent system inefficiencies.



A word of advice. Insulation will provide the biggest bang for the buck. Insulate the living stuffing out of the house first, replace what windows you can and then have an energy audit performed, and seal the home up, and you will be better prepared to replace the boiler for your home, with a much smaller boiler.



You can then relax and enjoy the comfort and fuel savings.



ME

Baggins

Re: Bad News

Kettling indicates a continuous fresh water make up leak within the system that introduces excess minerals...







Maybe I don't really know what kettling is?  This system doesn't have a

continuous make-up as it is fundamentally a closed system and only gets

new water if I add it to the system manually.







The noise I get  sounds like rocks rattling around inside the base of

one of the main top out flow pipes (3)  Note I did not have this before I

flushed out the system







Is the above sound consistent with what kettling sounds like?







Thanks



Dan

Mark Eatherton

Well, that's GOOD news...

If you are the sole responsible person charged with filling the boiler, then you'd KNOW if there was a leak. Kettling, as the name implies, sounds like a tea kettle boiling. It is usually associated with a bouncing pressure gage as the steam bubbles jump into the water.



It may just be because of all the fresh water you've induced into the system, which carries a lot of oxygen. This oxygen has to be removed through the process of boiling, and metal oxidation. Once the supply of oxygen is exhausted, the kettle should quiet down.



What you may have also done in your effort to flush the nasties out of your system, is to block flow to certain parts of the old cast iron boiler, causing hot spots that would have a tendency to flash to steam.



Lastly, there is a possibility that the boiler is over fired, although you did't mention anything about having done any work on the fire side of the system.



ME

Baggins

Let's hope

then you'd KNOW if there was a leak..... agreed  ... the one thing that is difficult for me to tell is  .. if I am cooking off fluids during fire  . ..because the expansion tank in the attic is pretty difficult to get to and measure its level of fluids



What you may have also done in your effort to flush the nasties out of

your system, is to block flow to certain parts of the old cast iron

boiler, ... that's what I am wondering also, is that maybe I have settled 50 years worth of sludge at the bottom of the feed line ... causing a bit of a problem .... I have read  that sulphamic acid flush may help ... but I have no idea if that is the case or not .. if it needs major work I would like to attack during the off season...



Thoughts on a more aggressive flush??



Thanks

Dan

Mark Eatherton

Got pictures????

I'd need to see the near boiler piping to say whether its even feasible to do a power flush on the system, but experience with older solid fuel conversion boilers tells me that the installers didn't provide adequate purge points and isolation to make the job easy.



Show us what you've got.



ME

Baggins

With pics

Photo 1 - exterior view - top horizontal door opens to heat exchanger, lower door opens to burner



Photo 6 -  is an inside shot of the heat exchanger, the darker color towards the back right is the quote, unquote "moist" area



Photo 7 - is a shot of the burner -- it probably needs a nickname



Photo 10 - is a shot of the top exterior .. note: encapsulated asbestos ..  vertical pipe to the right of the elbow and the altitude gauge .. it is at the base of this that noise seems to emanate from .. bumped out collar should be where the flanges join each other.



ok so now we have pics, does this help at all?



Thanks

Dan

Mark Eatherton

Going to be tough...

The boiler piping is not conducive to power purging. Not enough isolation, and you will have to abate the insulation before anyone can do anything to the boiler.



This system is still set up for gravity?



I'm thinking the best you will be able to do, short of complete replacement, is the Rhomar water conditioning.



As for the moisture, I still think it os more than likely condensation as opposed to an actual vessel leak, but without performing a hydrostatic vessel test (not recommended on a boiler of this age) you will never know.



If I were you, I'd seriously start saving your money for a replacement... The Earth will thank you :-)



ME

Baggins

looking to replace

Ok, so if I resign myself to the obvious



do I design to feed and take from  the existing 3" flange points?



is there a preferred brand? ( I've looked mostly at Weil-mcClain)



Thanks

Mark Eatherton

I'd abate everything in the mechanical room....

If the basement is your mechanical room, then I'd abate to the first branch tees.



As for type, I prefer Lochinvar, but don't dedicate yourself to a particular brand. Its more important that you become comfortable with the installing contractor. The only thing I'd consider avoiding, is the use of aluminum, which the Weil is....



Make certain that your contractor of choice has a digital combustion analyzer, and that they know how to use it.



ME

Baggins

making sure I understand

1. if the basement is your mechanical room, then I'd abate to the first branch tees

I want to make sure that understand what you are saying in the above...



Are you saying to remove as much of the existing piping as possible and to connect to the last "Tee" in each feed and return line whenever I can?



Thanks

Dan

Mark Eatherton

Clarification...

You need to remove enough asbestos to insure that the installers will NOT have to disturb any of it. If you have them abate to the first set of branch tees down stream of the boiler, it should be enough.



Your system is most probably piped parallel direct return, and you shouldn't have to change that.



ME