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Buderus R2107 reading high outside temperature

Stelcom66 Member Posts: 23
I posted about this happening about 3 years ago. A couple days ago for the first time since then the system again was reading a constant high outside temperature, this time 104º when it was about 75º outside. I installed a resistor on a switch 3 years ago to create a reading of 30 degrees. Moved the switch and the temp did read 30º and the circulator started. I then moved the thermistor back and forth a couple times, put the switch back to normal and then the temp was correct. After that I did loosen/retighten the thermistor connection.

My original plan was to buy a couple different types of thermistors to have on hand. Never needed to, and now unfortunately my company made us part time last year due to the pandemic but kept us that way. Every bit of expense now especially counts. I may still order a few online or check a local store that (luckily) is an electronics components store.

I do wonder if anyone has seen this with a Buderus R2107. I'm hoping it is just the thermistor itself and not the control unit. It seems to be given when I connect the 32k ohms it reads 30 degrees.


  • ratio
    ratio Member Posts: 3,173
    See https://forum.heatinghelp.com/discussion/168102/buderus-outdoor-sensor.

    Note that there are several different kinds of 10k thermistor (type II and type III AKA CP and AN) and with the range you need for an outdoor sensor it's going to make a difference. You should be able to figure out the exact type by sticking a few other resistors in place & seeing what temperature pops up. Use the table at https://www.workaci.com/sites/default/files/category-files/Thermistor Temp Curve_7.pdf to figure out exactly which type you've got, then order on of these: https://www.workaci.com/catalog-new/outside-air-2

  • Stelcom66
    Stelcom66 Member Posts: 23
    Thanks for the informative references. My system may use a ACI/10K-CP type thermistor - that column shows about 32k ohms at 32 degrees. Like you said, I have many resistors on hand and can see what they end up showing for a temperature. I even have a step type resistance wheel with many values on it. They're probably only 1/4 or 1/8 watt but that should be fine to test with. Back in the day Radio Shack probably sold an assortment 10 pack. Boy do I miss them!
  • Big Ed_4
    Big Ed_4 Member Posts: 1,882
    Normally it's the outdoor sensor it could also be the wire .....
    I have enough experience to know , that I dont know it all