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.

Vitodens 100-w firing - supposed to be back-up for outdoor boiler

Hi - My vitodens 100-w boiler is supposed to only fire when the water temperature in my outdoor wood boiler (OWB) falls below 140 as it enters the house - but the inside boiler has been firing a lot given the very cold weather we've had in Upstate NY, even though the OWB water temperature remains at 160-180. I assume this is due to the outdoor sensor. I would like to disable the outdoor sensor. Anything I should be concerned with if I do disable the outdoor sensor?


  • Jamie Hall
    Jamie Hall Member Posts: 18,968
    edited January 2018
    You might do better to check what the outdoor sensor's curve is set for, and see if you can persuade it that even in very cold weather it will maintain a higher return water temperature.

    Poor thing is just trying to keep you warm, after all!

    Of course that will defeat the efficiency of the condensing...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SkipMuck1
    SkipMuck1 Member Posts: 2
    Thanks Jamie. I'm not so concerned about the efficiency of the condensing boiler because its a back up system and should rarely, if ever, turn on.

  • hot_rod
    hot_rod Member Posts: 16,327
    What type of control tells it when to turn on, maybe check to see if that is calling it on prematurely.

    Does the Viessmann have a freeze protection function? maybe it senses that low outdoor and exercises?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    edited January 2018
    It would be best to pipe the wood boiler into the system before the low loss header or hydraulic separator. The sensor in the LLH will tell the boiler when to supply supplemental heat. I'm not sure if the V100 has a control terminal or accepts a LLH sensor. The V200 does.