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[Solved] Bosch Thermostat II - inflated temperature, plan not working, what to set in the app?

marek_0116 2148 10
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How do I fix a Bosch Smart Home Thermostat II that keeps a radiator at about 26°C regardless of the set temperature?

Recalibrate the thermostat head again, because the head learns the valve’s working range during calibration and a bad calibration can make it regulate incorrectly [#21712791] If the pin travel is too small or the valve is stiff, the head may not close the valve fully even though no error is shown, so it is worth checking the actuator stroke and the valve movement [#21712241] One useful check is to set the thermostat to pause heating: if the radiator becomes cold then the valve can close properly, which points back to calibration rather than a missing gap between the head and valve [#21712214] In this case, after recalibrating once more, the thermostat started working as expected [#21715421]
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  • Calibration or app settings causing 26°C overshoot

    #1 21711627
    marek_0116
    Level 5  
    Posts: 19
    Hi, I have this problem.
    I have bought a Bosch thermostat II head for the radiator in my flat. For this I bought a Bosch Smart Home Driver II controller and installed the Bosch Smart Home app.
    I have connected everything, theoretically it works.

    The problem is that the head heats too much. I set myself a schedule. It's supposed to heat at 22.5 degrees at night and drop to 17 degrees during the day. However, the head maintains a temperature of around 26/26.2 degrees.
    Any suggestions as to what could be wrong?
    I have reset the head, done the calibration again and still the same. Bosch Smart Home screen shows measured temp 26.2°C and setpoint 17.0°C in bedroom
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  • #2 21712214
    szamotel
    Level 18  
    Posts: 181
    Help: 25
    Rate: 96
    If you close the head completely so that the heating is off, is the radiator warm or does it cool down? If the radiator is warm even though the head is closed, it means that there is a gap between the head bolt and the valve and some distance needs to be used.
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  • #3 21712224
    marek_0116
    Level 5  
    Posts: 19
    When I reduce the temperature to 5 degrees (that's the minimum), it still holds that 26 degrees.

    But in the app I have an option to pause heating, when I turn this on then the head closes completely and the radiator is cold. So it's unlikely to be the fault of play between the pin and the valve.
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  • Calibration may be failing due to valve pin resistance

    #4 21712241
    szamotel
    Level 18  
    Posts: 181
    Help: 25
    Rate: 96
    At 5 degrees the radiator should be closed, apparently the calibration was not done correctly. Maybe the radiator head pin pushes in with a lot of resistance and the Bosch head detects the resistance during calibration and the radiator valve is not completely closed. You can measure the stroke of the head after calibration (close - open) and compare with the stroke of the needle of the radiator valve.
  • #5 21712254
    marek_0116
    Level 5  
    Posts: 19
    It seems to me that if it detected too much resistance, it would throw an EO3 error (at least that's what it says in the instructions).

    As for the head pitch after calibration - I hadn't thought of that, I'll measure it and see what it looks like. Thanks for the hint
  • #6 21712290
    płetwa
    Level 33  
    Posts: 1992
    Help: 165
    Rate: 553
    Is the head covered by a curtain or drapes? I ask because the sensor is in the head and if you obscure that then there is no precision.
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  • #7 21712297
    marek_0116
    Level 5  
    Posts: 19
    It is not obscured.
    We could talk about precision if the difference was 1 or 2 degrees. And not that I set it, no matter if it's 17 degrees or 5 degrees, and it heats me up around 26 degrees 😂
  • #8 21712303
    płetwa
    Level 33  
    Posts: 1992
    Help: 165
    Rate: 553
    Send a link to the instructions. I wonder if the adjustment is proportional or 0.1.
  • #9 21712305
    marek_0116
    Level 5  
    Posts: 19
    It seems to me that if it detected too much resistance, it would throw an EO3 error (yes, at least it is in the instructions).

    As for the head pitch after calibration - I hadn't thought of that, I'll measure it and see how it looks. Thanks for the hint
  • #10 21712791
    szamotel
    Level 18  
    Posts: 181
    Help: 25
    Rate: 96
    During calibration, the head works from resistance to resistance and so learns the working range. There can be an error if the firing pin stroke is too small.
  • #11 21715421
    marek_0116
    Level 5  
    Posts: 19
    I calibrated the head once again and so far it is working as it should.
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Topic summary

LABEL_AI_GENERATED
A Bosch Smart Home radiator thermostat head was heating the room to about 26°C regardless of the scheduled setpoint, even when the app was set to 17°C or the minimum 5°C. The installation included a Bosch Smart Home Controller II and the Bosch Smart Home app. Initial troubleshooting focused on valve clearance, calibration, and possible obstruction by curtains, but the radiator was confirmed to close and cool down when heating was paused, indicating the valve could shut properly. The most likely cause was an incorrect calibration or an incorrect learned stroke range of the thermostat head. After recalibrating the head again, the system started working correctly.
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