Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.
If our community has helped you, please consider making a contribution to support this website. Thanks!

Boiler Protection with 3-way valve?

Options
AlwaysLearning2024
AlwaysLearning2024 Member Posts: 96
in THE MAIN WALL

Hi everyone!

Learning more about boiler protection for my CG 8 cast-iron boiler.

I finally understood the concept of the minimum temperature needed to prevent condensation and the reason why my boiler control (TekMar 256) is managing this and the boiler is short cycling a bit in mild-weather to maintain this 140 degree minimum YET the building is too hot and consuming unnessary gas to provide this protection.

I learned here on these forums (thanks @Boilerpro_3, @Jeffrey A. Knichel and others) that a Danfoss ESBE Thermic By-pass Valve could help with this situation.

Would this be a solution for my applciation?

Do I have this arrangement correct?

Thanks for any help!

Nicholas

Screenshot 2025-11-19 at 11.59.17 AM.png

Comments

  • hot_rod
    hot_rod Member Posts: 26,590

    I'm a bit biased working for Caleffi, but the 280 is an excellent valve for boiler protection. High Cv, union connections, temperature gauge wells, multiple temperature sensors available.

    We sell many of these around the world. They are standard equipment on most wood fired and pellet fired equipment to prevent cold operation which leads to creosote formation. So the manual talks about that type of equipment.

    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Caleffi-280975A-Product%20Overview.pdf

    Screenshot 2025-11-19 at 11.10.42 AM.png

    Regardless if you use a valve or electronic solution, the boiler needs to operate to maintain that temperature.

    But with a protection valve, shut the boiler off, after the heat call cold start will lengthen cycles and boost boiler efficiency compared to short, under 10 minute cycles.

    The type of heat emitters matters, copper fin tube rarely need boiler protection.

    Cast rads or large high water content, like gravity conversions, really need protection.

    Combining zones helps eliminate shoulder season short cycling. But zoning is a selling feature of hydronics :) catch 22.

    In mild conditions it will be hard to eliminate short cycles without maybe tricking the boiler with a anti cycle timer for example. Holding the boiler off when there is a call for heat has some consequences. Comfort might be higher on your list that absolute energy savings?

    These are all the challenges with fixed output boilers facing a very wide, dynamic heat load throughout the season.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    AlwaysLearning2024HomerJSmith
  • AlwaysLearning2024
    AlwaysLearning2024 Member Posts: 96

    Thank you @hot_rod .

    Yes, fin-tube heat emmiters. Yes, this is the mild season a bit and 140 degrees is plenty warm enough with outside temps in the mid 40's - yet still need to heat the building. I guess I was trying to mitigate the TekMar keeping the boiler at 140 when the building doesnt need the heat. There is no call for heat currently. Just the boiler is on, with contacnt circualtion and the Tekmar keeping the temp up to mitigate condensation.

    Basically trying to tame the horsepower of the CG8! I guess the lowest "setting" of 140 degrees for the boiler is still to warm and will just need to accept the loss of $$ in the mild season?

    Once colder weather arrives, true call for heat will be made and temps above 140 will be realized?

    Would you explain why I woudn't need a bypass for fin tubed?

    Thank you!

  • hot_rod
    hot_rod Member Posts: 26,590

    yes you are battling a very common occurrence. Over-sized or grossly over-sized boilers make it a no win endeavor.

    Boiler block or SWT needs to be above 140F to get return to at least 130. Weil seems comfortable with 130 RWT.

    What you may find it the boiler cycles off before return gets warm enough.

    Or the heat call goes away before reaching adequate temperature.

    ALL systems strive to reach thermal equilibrium, more about that here. It you are still "always learning"

    https://www.caleffi.com/en-us/magazine/23-heat-transfer-hydronic-systems

    Or a shortened version

    Screenshot 2025-11-19 at 12.29.00 PM.png Screenshot 2025-11-19 at 12.29.27 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    AlwaysLearning2024
  • AlwaysLearning2024
    AlwaysLearning2024 Member Posts: 96

    Thank you, @hot_rod . Yes, always learning! In my case, am I a bit stuck with this scenario with an oversized boiler?

    Yestrday in Cincinnati we had an abnormal mild day (high 40's to low 50's). Eventually, due to the outdoor reset setting on the Tekmar 256, the boiler cooled. Inside temps were fine. In the evening., the outdoor temp dropped, eventually triggering the firing of the boiler. The water temp before firing was around 73 degrees. Is this the condition that condensation of flue gasses / heating block danger occurs?

    Or is this when the heating block is hot and the return water is cool?

    Thank you!

Categories