Odd ESP8266 behaviour

I had a project to build 2 or 3 environment sensors for my home automation setup.

Wemos Mini D1 R2 + a BME280 sensor.
The firmware was prewritten, pretested and already running 2 or 3 sensors around my house. So it's known working.

I soldered the first one together, plugged it in and flashed it with the firmware. It immediately connected to the Wifi and started working. WooHoo! As it should be.

However I noticed a small issue so I updated the code and reflashed. This time however it would not connect to the network. I left it for 5 minutes, no connection. I powered it off and on again several times and nothing. Flashing LED spinning waiting on Wifi status to be connected. No sign of it on my Wifi clients list or DHCP.

So thinking I'd somehow killed it or bought a dodgy one, I soldered up and new one. It connects fine, same firmware. So out of interest I plugged the original one back in and ... it connected straight away.

Something is upsetting them, or the ESP is upsetting my Wifi router which is then blacklisting them temporarily. I'm surmising.

Has anyone seem similar? Any suggestions?


Almost anything is possible. We have less than 1% of the information and we might come up with 100 suggestions :o

The router blocking an IP might be possible. Perhaps you can find that in the log of the router.

The ESP modules seems to remember a previous Wifi connection.

When you upload a new sketch, it might use the Wifi settings of the previous sketch. With that in mind, everything gets very fuzzy. You might never find the cause of the problem. If it works now, then it is okay.

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