Video of working WiFi

I am going to try it on tomorrow’s brew. Wish me good luck!

OK, The test run well before boiling. However, EMI attacked and the LCD blinked with random patterns. ESP8266 has nothing to do with EMI because I had it before using ESP8266. I should have fixed this before. In fact, I couldn’t see the LCD in the middle of MASHING, but the ESP8266 worked fine and I could check the status on my iPhone. After Mash-out, I quit the automation, power recycle the system, and resumed the brew. Everything was fine until boiling point was almost reached. The connection between Arduino and ESP8266 lost. I still could connect to ESP8266 by my iPhone, but it was not able to connect to Arduino. After the brew finished, everything went bak to work normally.
I am not sure if it is a hardware(bad connection) or software issue. ESP8266 requires peak 500mA power. If the power supply is not enough ESP8266 would be very unstable. “Thanks” to my bad soldering skill and loose hardware connections, I had some experiences about it. ( I “fixed” it by place the boards at different places.) Further investigation is needed.
To Robert,
Basically, just connect the SERIALs, software or hardware. I have tried the following configurations successfully. You have to change the definition in the source code, of course. I think the divider method will also work.
(The pictures of the boards are copied from other sites. If it infringes your right, please let me know.)

Picture sources:
NodeMcu: https://github.com/nodemcu/nodemcu-devkit-v1.0
Arduino:https://www.arduino.cc/en/Tutorial/EEPROMClear
convert board: aliexpress