CO2 Sensor reports -3 on DIY Pro Kit Pre-Soldered

Currently my DIY Pro 4.2 is reporting -3 for CO2. Even after re-flashing it with official firmware according to this page
It is [DIY Pro Kit Pre-Soldered (version 4.2)]
When I first turned the device on, it seemed like working fine, with some random CO2 reading.
I then flashed with with ESPHome integration following these forum posts: AirGradient DIY and HomeAssistant - Third party integrations - Home Assistant Community

I used multiple ESPHome configs like:

  1. From @ajfriesen Andrej Friesen :
  2. From @MallocArray :
  3. From peter.vk : /t/airgradient-integrations/703/6

None of them shows CO2 value. It shows nan
And now to verify that it works with official AirGradient firmware, I re-flashed it with official version, now it shows -3 . See attached photo.
I have not done anything to the soldering or the sensor itself.

Can someone point me to how can I debug this and verify if it’s software or hardware problem ?

Could you post some pictures of the inside, where your ESP is connected, as well as the S8 sensor? Or touch up all of the solder points, as often it is just a weak solder connection that causes trouble, or a small bridge of solder.

The soldering looks fine. I’m attaching few photos here.
[One photo per post because I’m new user.]

@AirGradient Can you help with this please.

Please test the solder points on the S8 and also on the D1. This often fixes these types of issues.

@AirGradient Sorry, how do I test them ? (I don’t have a multimeter)

Hello again,
I checked all the solder joins. They all are securely connected, without any bridging/shorting and also no loose connections. This is what I would expect from pre-soldered version, as it’s done by professionals.

Still the CO2 reading is -3.

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