Scrape tempartures from fireplace with water heating function from network control panel

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Hello,
my fireplace with a water heating function in the livingroom has an control panel, avalible in my home network.
I tried to scrape some temperature data from this site, but the Sensor just shows —°C
Have anyone some idea, what could be the problem?

image
image1132×543 61 KB 

here my scrape code:
'''
scrape:
  - resource: http://<ip from controlpanel>/
    scan_interval: 5
    sensor:
      - name: Firepit temp
        unique_id: sensor.firepit_temp
        select: "#teplotaUdaj"

→ the state is shown with “—°C”

Thank you.