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Gravity Hot Water..HMM

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cleve
cleve Member Posts: 3
Over the weekend I had a service call on a HW Gravity system. I arrived to find the upper floor airbound- purged the upper radiators-- and verified flow with an IR thermometer -it was clear that the supply came off the top of the boiler, and the return came in the side- I was looking at a 30 degree delta T. Everything was great-- The boiler was running and the space started to heat. The boiler came up to temp, the aquastat stopped calling--just as I was about to walk out the door I shot the supply & return with the IR thermometer. What the heck... the supply was now 120 and the return was now 165. I gave it a little thought and talked myself into a water density issue in the the cold- dense return water was pushing back the hot water on the off cycle. I thought to myself how much could be learned with the IR thermometer- there was something I had never seen before. I grabbed the piping- my hands were telling me my thermometer was correct. I waited for the aquastat to call again-and once it had started heating- and the supply heated up to 175-- and the return was now 145. Life is great. I left.
6 hours later-- the recall comes back--I arrived to find the boiler running-- and the supply piping ( on the top of the boiler at 130) and the return ( on the side of the boiler at 165). At this point, I don't have an explanation on how the supply and return- could swap. I read once where piping it backwards could reduce thermal shock, but how a flow could change on cycles alludes me. Any insight?

Comments

  • Ironman
    Ironman Member Posts: 7,379
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    Where was the expansion tank on the system and why did it become air bound?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • cleve
    cleve Member Posts: 3
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    The Compression tanks ( 2 coming off a bull headed tee) were piped to the same tapping as the pressure relief valve- on the side of the boiler). The old open expansion tank had long been abandoned in the attic.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,607
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    Beats me. But I can think of one thing to check.

    The combustion chamber.

    I don't know if your gas or oil fired, doesn't really matter but the fire brick inside the boiler usually is brought up 4-6" above the bottom of the boiler section which is usually referred to as the water leg, some call it the "mud leg". One reason for this is that the lower part of the boiler will collect any mud or sludge which will act as an insulator and could cause the flame to overheat the boiler section. To protect against this the combustion chamber is brought above the bottom of the boiler to protect the section from direct heat from the flame.

    My point is if the combustion chamber has deteriorated and the bottom of the sections are getting hot this might cause reverse circulation
  • Ironman
    Ironman Member Posts: 7,379
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    Or, if the mud leg was sludged up...
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • cleve
    cleve Member Posts: 3
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    Thanks gents.. these are all good things to be looking at.
    I really dread draining things down-- the 2" mains and CI radiators hold a lot of water- which equates to eternity trying to fill and purge. Having said that-- there's never the easy fix to any problem
  • Ironman
    Ironman Member Posts: 7,379
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    If it's doing the job now, I'd certainly wait til warmer weather.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • leonz
    leonz Member Posts: 1,154
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    Ugh,

    It needs some work; is it still a gravity fed boiler or is there a circulator someplace in there??

    B+G wants their compression tanks cross connected in parallel with shut off valves and airtrol valves installed in the bottom of each of the compression tanks to drain excess water and to create the cushion if more than one steel compression tank is used.

    They also want the steel compression tanks above the steam chest hanging in the floor joists

    Is there gauge glass in each of the compression tanks?

    May be best to just wait and drain it flush out the boiler completely, fix the plumbing job by repairing and installing the steel compression tanks the right way or installing an expansion tank in the attic with a hot water return loop to the boiler or cross connect it to the highest radiator in the living space just as Dan shows us in his books. with the relief and vent line going to the basement drain if they no longer want a vent through the roof.

    I see the dead men shaking their heads.