DS18B20 freaking out / continuously reporting 85°C


So I installed a DS18B20 temperature sensor in my heatpump.

Code is:

  name: heatpump-gateway
  platform: ESP32
  board: esp32dev

# Enable logging

# Enable Home Assistant API
  password: "XXXXXXX"

  password: "XXXXXXX"

  ssid: "XXXX"
  password: "XXXXXXX"

  # Enable fallback hotspot (captive portal) in case wifi connection fails
    ssid: "XXXXXXX"
    password: "XXXXXXXXX"


  - pin: 26

  - platform: dallas
    address: 0x0B01205F7A417828
    name: "Heatpump Lower Temperature"
  - platform: dallas
    address: 0x5101205F66BBD928
    name: "Heatpump Upper Temperature"

As you can see in the following screen, it continuously repots back 85°C, whilst it also reports the correct values (like switching from correct to wrong all the time):

Any idea why this happens?


No logs, no issue.

How long are the cables to the sensors?

What value pull-up resistor did you use?

85°C on DS18B20 almost always means powering issues.

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reported temp 85 degrees in case of DS1820 means that you don’t have a connection with sensor, not that it’s “freaking out”. No sensor connected will return 85. Check length of your cables → power supply to the sensor - do you have parasitic power? It can cause problems. Like tom said: power supply issues or communication issues.

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Might be a “new” fake ds18b20 with a special feature set?


I guess if you have posted logs we would have seen that the one wire bus resets after each reading and therefor starts again with the power-up temperature of 85°C

Sry for my late reply to you all.

I wasn’t at home and will check everything in the evening but I don’t think it’s about the length of the cable as I use the same temerature probe on the same ESP32 for the lower temperature of the heatpump.

Maybe it is about some hardware-connection / soldering problem then.

Ok, so it was just a loose cable / a bad contact.
Everything is working now.

Thanks for your support!