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Boiler temp question

louiss
louiss Member Posts: 2
in Gas Heating
I have a Biasi B10 oil fired boiler. Recently replaced a bad aquastat, so was keeping a closer eye on it than usual. I noticed the temperature on both the aquastat and the analog gauge hit 210 degrees. I had always thought a boiler needed to be kept below 212.

Further investigation: the aquastat is working correctly, high limit set to 170 and boiler stops firing at that temp. But if no zone is calling for heat, the boiler temperature continues to rise another 40 degrees. Climbs less if a zone wants heat and draws it from the boiler, of course.

Two questions: (1) is coasting another 40 degrees after it stops firing normal? I expected some overshoot, but that seems like a lot. (2) Is a peak of 210 degrees too hot? No other issues, pressure is 25psi, no odd noises, pressure relief valve not tripping, etc

Thanks!
Lou

Comments

  • bburd
    bburd Member Posts: 1,031
    edited January 20
    What you are describing is normal. Remember that with the system pressurized, the boiling point is much higher than 212°F.

    Automobile engine cooling systems are pressurized to 15 psi and will not boil unless they exceed 260°F. 
    —
    Bburd
    louiss
  • Big Ed_4
    Big Ed_4 Member Posts: 3,012
    I would first check to make sure the capillary of the new aquastat is fully inserted into the extended well ......

    There was an error rendering this rich post.

  • bburd
    bburd Member Posts: 1,031
    Big Ed_4 said:
    I would first check to make sure the capillary of the new aquastat is fully inserted into the extended well ......
    There should be some heat conductive paste in there also.
    —
    Bburd
  • Big Ed_4
    Big Ed_4 Member Posts: 3,012
    I have not seen the paste in years. It was used to change from the old Series 10 , helix aquastat to capillary . It was dumb back then , better off changing the well .

    Out of the box the lengtht is set for a standard well in a new aquastat . With the extended well one needs to pull out the extra tubing to bottom out the capillary . Normal problem ...

    There was an error rendering this rich post.

    bburd
  • hot_rod
    hot_rod Member Posts: 23,275
    Has the boiler had a good cleaning lately?

    You could add a post purge function and send some of that heat energy out to the system, maybe?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,400
    The OP said the HL is set to 170 and the boiler stops firing at that temp. So there is nothing wrong with the aqustat or well.

    It is simply residual heat
  • louiss
    louiss Member Posts: 2
    Thanks, all. Yes, it's just residual heat (I actually didn't change the sensor as I went from a hydrostat 3250 to a 3250+).

    What surprised me was the amount of temp increase from residual heat. I get that it's cast iron, but didn't expect a 40 degree swing. If that's normal, then it's working correctly

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