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boiler water line

sig Member Posts: 13
I just replaced a boiler that developed a hole at the top of a section after just 5 years (I did not do the original job and I have no prior knoweledge of this building). But knowing just enough about steam to be dangerous I replaced the failed boiler with the exact model and made sure I protected myself in my contract against any system problems.  Well as predicted there are problems (some radiators don't heat and if the automatic water feeder is left on the boiler floods) and although they are not in my price I am expected to offer a solution to fix them. 

The system is a mix of one and two pipe with some of the two pipe radiators controlled by a danfoss valves and others with no apparent automatic valves or traps....just normal looking radiator valves and steam vents.  I have not located any main traps either, just main vents.

The original boiler is still in place in the boiler room.  It is abut three times the size of the new boiler and was orignially coal but converted to oil some time ago.  The opening to feed the coal orginally was about 4 ft. tall which put the boiler (which was much lager to begin with)  on a 4 ft. pedistal.  That made the original water line about 6 to 8 ft. higher than the new boilers water line.  Note: The new boiler's headers are sized and installed correctly. 

It seems to me that I need to install a false water line to bring the system to the original water line as my first step.  Any thoughts or suggestons would be great.


  • Jamie Hall
    Jamie Hall Member Posts: 23,635
    A good place to start

    if you don't have them is Dan's books, available on this site (I sound like an advertisement... but they really are worth it!).  That said...

    A very common problem in the type of retrofit you did is that water line.  It is not at all unusual to have the end (or sometimes elsewhere) on the steam mains drop to a wet return, and to have the ends of the dry returns drop to the same wet return.  If the water line is too low, there is no water seal between the to and steam gets into the dry returns -- presto, no heat.  The easiest solution, as you note, may be a false water line, since it sounds as though putting the new boiler up so that the water lines would be the same would then require a ladder for servicing!

    Second, there should be no need for a vent on a two pipe radiator, although it won't hurt anything.  The air and condensate should go out -- usually through a trap, but sometimes through an orifice or other seal -- into the dry return; the air then goes to a main vent, and the water back to the boiler.  If the return from the two pipe radiators is yeouch hot (not just warm) you may be getting steam into the return through the radiator, which is another way to shut down a two pipe system.  Depending on the type of system, you may need to throttle those radiators which offend, or replace the trap or whatever to bring them back to design.

    A one pipe radiator which doesn't heat isn't getting steam (yeah, I know, that's one of those remarks.  Oh well...).  Either the air isn't getting out -- bad vent -- or there is something, such as a sag or a badly pitched pipe -- which is letting condensate block the flow.  Or even a bad valve!  Or one which doesn't belong.  I would trace out the riser to those radiators when the system is running, and see how far along steam is getting -- that may produce a hint as to what's wrong.  Same sort of logic applies to a two pipe radiator, except for the vent.

    Do not check a one pipe radiator's vent by removing it when the system is running -- if it is the vent, you'll get steam out of the resulting hole, which can burn very badly!  Also removes wallpaper...

    Check your system pressure -- no more than a pound an a half, and less (say 10 to 12 ounces) is better, if your controls will let you do that.

    Just a few thoughts -- by no means exclusive!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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