Same problem here. Picked up a new SHT30 online and it’s now working as expected.
I have this same problem, I ordered the diy pro kit and assembled it recently, right off the bat the temperature and humidity readings were zero. While building I removed the two pullup resistors from the SHT31 board as instructed. After finding this thread I tried installing some 2.2k resistors I had laying around and that got the temperature working most of the time but now the TVOC is stuck showing zero and occasionally the temperature still drops out. Today I saw the CO2 value drop a few times as well but so far the display is working fine. Did anyone ever find a conclusive solution to this? I’ve built quite a few gadgets around the ESP8266 and various I2C sensors and I’ve never had problems like this. I took a cursory glance with a scope right after I built it and saw reasonable looking activity on the I2C bus but it’s pretty hard to tell which data I’m looking at. In the meantime I ordered another SHT31 to try but I’m still waiting for that to arrive.
Try to update to the latest AirGradient Arduino library. We made the CO2 readings much more robust in the last update.
I already had the latest libraries. I ordered another SHT31 module from a random Chinese seller, that arrived recently so I soldered on the header and popped it in today and now it’s been rock solid so far. I’m really curious why people are having problems with these sensors, maybe there is a bad batch that has an unusually high failure rate, maybe counterfeit parts? I don’t know, but the replacement I bought looks identical to the one that came with the kit and it works perfectly whereas the other one was flaky from the start. The only difference in the process is originally I removed the pullup resistors as instructed and this time I left them as-is and installed the module as received.
What I often see is that even solder points that look good are actually not working well. So reflowing the solder often helps.
We use the same SHT module in our commercial monitor that we test every unit and never had an issue. So I do not think the module has wide spread issues.
I have >30 years of soldering experience, including some time doing it professionally so I don’t think that was the problem. I suppose it’s possible ESD damaged it since I built the thing on my coffee table so I could sit on the sofa instead of hiding out in the lab but who knows. Whatever the case it’s working great now.